Abstract book final - International Conference on Strongly

Transcription

International Conference on
Strongly Correlated Electron Systems
Abstract Book
Organized by
Center for Correlated Matter, Zhejiang University
Department of Physics, Zhejiang University
Collaborative Innovation Center of Advanced Microstructures, Nanjing
May 8– 13, 2016
Hangzhou, China
www.sces2016.org
Contents
Plenary Sessions............................................................ ..............................................1
Parallel Sessions...........................................................................................................9
Poster Sessions....................................................... ...................................................120
Monday.............................................................................................................121
Tuesday.................................................................. ....................................... .229
Wednesday................................................... ....................................................332
Plenary Sessions
(Venue: Opera)
1
Mo-P-1
Opera
Monday 8:30-9:15
Is the high Tc superconductivity in cuprates an interface problem?
Qi-Kun Xue
Tsinghua University, Beijing 100084, China
We investigate the pairing mechanism of high Tc superconductivity in cuprates by
using state-of-the-art molecular beam epitaxy (MBE)-scanning tunneling microscopy
(STM). By two different approaches in sample preparation, namely Ar+ ion
bombardment and ozone-assisted MBE growth, we are able to study the gap structure
of superconducting copper oxide planes in unprecedented way. We show that the
Cooper pairing in cuprates is rather conventional and the unique interfacial structure
plays a crucial role in the high temperature superconductivity.
The author acknowledges Xucun Ma, Canli Song, Lili Wang and Genda Gu (BNL)
for collaboration, and the financial supports from National Science Foundation of
China, and Ministry of Science & Technology and Ministry of Education of China.
2
Mo-P-2
Opera
Monday 9:15-10:00
Entropy Landscape of Heavy-Fermion SystemsNear Quantum
Criticality
Hilbert v. Löhneysen
Karlsruhe Institute of Technology, Institute for Solid State Physics, 76021 Karlsruhe, Germany
In a number of materials, second-order phase transitions can be driven to zero
temperature by a non-thermal control parameter such as pressure, magnetic or electric
field, or composition. The origin of this unusual effect often arises from competing
interactions. An example is the competition between the Kondo effect leading to local
singlet states and the RKKY interaction favoring long-range magnetic order. As the
temperature T is lowered towards absolute zero in the vicinity of such a quantum
critical point (QCP), quantum fluctuations become increasingly important. They lead
to unconventional scaling behavior of thermodynamic and transport properties and an
accumulation of entropy at very low T, thereby allowing new types of electronic
excitations and new phases. The enhanced entropy S when approaching a QCP can be
probed by measurements of the specific heat, and its dependence on pressure can be
studied by volume thermal expansion.
Anisotropic systems allow elucidating the nature of a QCP by employing multiple
tuning parameters associated with stress applied along different directions. This will
be shown for the heavy-fermion metal CeCu6-xAux which presents a canonical
example of a quantum critical system that can be tuned to a QCP (at x = xc = 0.1) by
composition or (for fixed x > xc) by hydrostatic pressure or magnetic field [1].
Inelastic neutron scattering studies of CeCu6-xAux have provided evidence of strongly
anisotropic quantum fluctuations [2] with unusual energy/temperature scaling [3]. We
have investigated the anisotropy of the thermal-expansion coefficients for x = 0.1.
Here, the directionally dependent stress Grüneisen ratios constitute a direct measure
of the presence and strength of thermodynamic singularities. We establish a procedure
to identify the combination of stresses that aims directly at the QCP and accomplishes
the steepest change of the entropy S[4]. We thereby can identify the optimal way to
approach the QCP and directly link it with the geometry of the underlying quantum
critical fluctuations. This new approach to quantum criticality allows uncovering the
scaling behavior of the associated singularities, and reveals a rich entropy
landscape.We will discuss results of this approach for other anisotropic
heavy-fermion systems.
References
[1] H. v. Löhneysen, A. Rosch, M. Vojta, and P. Wölfle, Rev. Mod. Phys. 79, 1016
(2007)
[2] O. Stockert, M. Enderle, and H. v. Löhneysen, Phys. Rev. Lett. 99, 237203
(2007)
[3] A. Schröder, G. Aeppli, R. Coldea, M. Adams, O. Stockert, H. v. Löhneysen, E.
Bucher, R. Ramazashvili, and P. Coleman, Nature 407, 351 (2000)
[4] K. Grube, S. Zaum, O. Stockert, Q. Si, and H. v. Löhneysen (to be published)
3
We-P-3
Opera
Wednesday 8:30-9:15
High Temperature Superconductivity – An ARPES Perspective
Zhi-Xun Shen
Department of Physics and Applied Physics, Stanford University
High-temperature superconductivity in cupper oxides, with critical temperature
well above what was thought possible, was discovered almost 30 years ago and
remains a major unsolved physics problem today. The challenge of this problem is
symbolized by a complex phase diagram composed of intertwined states with
anomalous properties in addition to unconventional superconductivity. None of them
can be described by conventional theory, thus compounding the difficulty to
understand high-temperature superconductivity itself as these states are different
manifestations of the same underlying physical system, making an integrated
understanding a necessity.
Angle-resolved photoemission spectroscopy (ARPES), has emerged as a leading
experimental tool to push the frontier of this important field of modern physics. Over
the last two decades, the improved resolution and carefully matched experiments have
been the keys to turn this technique into a sophisticated many-body physics tool. As a
result, ARPES played a critical role in setting the intellectual agenda by testing new
ideas and discovering surprises. This talk presents the insights we have gained on the
rich phase diagram of the copper oxide superconductors – by focusing on the low
lying excitations and energy gap spectra. Through the doping, temperature, symmetry
dependence, we reveal the intricate relationship between the superconducting gap and
the so-called pseudogap in the phase diagram. Such a comprehensive mapping of the
electronic phase diagram, including phase lines and mixed states inside the
superconducting dome, is difficult for conventional methods, and is likely a
pre-requisite for a complete understanding of high temperature superconductivity.
References:
ZX Shen et al., Phys. Rev. Lett. 70 1553 (1993)
D.S. Marshall et al., Phys. Rev. Lett. 76, 4841 (1996)
A.G. Loeser et al., Science, 273, 325 (1996)
K. Tanaka, Science 314, 1910 (2006)
W.S. Lee et al., Nature 450, 81 (2007)
M. Hashimoto et al., Nature Physics 6, 414-418 (2010)
R. He et al., Science, 331, 1579 (2011)
I. Vishik., PNAS 109, 18332 (2012)
M. Hashimoto et al., Nature Physics 10, 483 (2014)
M. Hashimoto et al., Nature Materials, 14, 1 (2015)
4
We-P-4
Opera
Wednesday 9:15-10:00
Quantum criticality, preformed pairs and spin liquids emerging near
Mott transition in quasi-triangular-lattice organics
Kazushi Kanoda
Department of Applied Physics, University of Tokyo, Tokyo, Japan
A many-body quantum system on the verge of instability between competing
ground states exhibits emergent phenomena. Interacting electrons on triangular
lattices are likely subjected to multiple instabilities in the charge and spin degrees of
freedom, affording diverse phenomena related to the Mott physics. The molecular
conductors are superior model systems for studying the Mott physics because of the
designability and controllability of material parameters such as lattice geometry and
bandwidth by chemical substitution and/or pressure. In this conference, I present
various quantum manifestations that interacting electrons in quasi-triangular-lattice
organics show on the verge of the Mott metal-insulator transition.
The topics include i) the quantum criticality of the Mott transition revealed by the
resistivity that obeys quantum-critical scaling, ii) the pseudo-gap-like behavior of the
metallic state, which is found to originate from preformed Cooper pairs that persist up
to twice as high as Tc, and iii) the spin liquid state that emerges in the Mott insulating
state, depending on the lattice geometry. I may touch the effect of disorder on the
Mott transition and the pressure-induced BEC-to-BCS crossover in a doped triangular
lattice.
The work presented here was performed in collaboration with T. Furukawa, H.
Oike, J. Ibuka, M. Urai, Y. Suzuki, K. Miyagawa (UTokyo), Y. Shimizu (Nagoya
Univ.), M. Ito, H. Taniguchi (Saitama Univ.) and R. Kato (RIKEN), M. Saito, S.
Iguchi and T. Sasaki (Tohoku Univ).
5
We-P-5
Opera
Resonant x-ray scattering explorations of charge order and broken
symmetries in underdoped cuprates
Riccardo Comin
University of Toronto, Canada
The spontaneous self-arrangement of electrons into periodically modulated patterns,
a phenomenon commonly termed as charge order or charge-density-wave, has
recently resurfaced as a prominent, universal ingredient for the physics of
high-temperature superconductors. Its antagonist coexistence with superconductivity,
together with its possible connection to a quantum critical point beyond optimal
doping, are symptomatic of a very fundamental role played by this symmetry-broken
collective electronic state.
Resonant x-ray scattering (RXS) has rapidly become the technique of choice for the
study of charge order in momentum space [1], owing to its ability to directly identify
a breaking of translational symmetry in the electronic density. We have used RXS in
underdoped Bi2201 and in electron-doped NCCO to detect charge-density-waves
even in presence of short-ranged order [2-3], exploring a realm previously accessible
only by STM. Furthermore, using the information available from the full
twodimensional momentum space, we have been able to demonstrate the presence of
charge stripes in YBCO [4]. In addition, the analysis of the polarization-dependent
scattering intensities revealed the local symmetry in the charge distribution around the
Cu atoms, which was found to be predominantly of a dwave bond-order type [5].
[1]R. Comin and A. Damascelli, Resonant x-ray scattering studies of charge order in
cuprates, Annual Reviews of Condensed Matter Physics (2016).
[2]R. Comin, et al., Charge Order Driven by Fermi-Arc Instability in Bi2Sr2−
xLaxCuO6+d, Science 343, 390 (2014).
[3]E. da Silva Neto*, R. Comin*, et al., Charge ordering in the electron-doped
superconductor Nd2-xCexCuO4, Science 347, 282 (2015).
[4]R. Comin, et al., Broken translational and rotational symmetry via charge stripe
order in underdoped YBa2Cu3O6+y, Science 347, 1335 (2015).
[5]R. Comin, et al., Symmetry of charge order in cuprates, Nature Materials 14, 796
(2015).
6
We-P-6
Opera
Microscopic mechanisms of spin-driven ferroelectricity and the
thermal Hall effect in insulating magnets
Hosho Katsura
Department of Physics, Graduate School of Science, University of Tokyo, Tokyo, Japan
I will discuss two intriguing phenomena that occur in insulating magnets (Mott
insulators) and their microscopic origins: (i) spin-driven ferroelectricity in
non-collinear magnets, (ii) the thermal Hall effect of magnetic (charge-neutral)
excitations.
(i) Based on a microscopic model including both electron correlation and spin-orbit
coupling, it was shown in Ref. [1] that the local electric polarization induced between
two spins can be nonvanishing when the spins are neither ferromagnetic nor
antiferromagnetic, i.e., non-collinear. This “local rule” is particularly useful for
predicting a new multiferroic material with a net polarization. In fact, this spin-driven
ferroelectricity has been verified in a variety of magnets with cycloidal (transverse
spiral) or transverse conical magnetic order [2].
(ii) Usually, magnetic insulators are not expected to exhibit (thermal) Hall response,
because the Lorentz force does not act on magnetic (charge-neutral) excitations.
However, in Ref. [3], two mechanisms of the thermal Hall effects without relying on
the Lorentz force were proposed. The first mechanism is based on the Berry curvature
of magnon wavefunctions, which is analogous to the anomalous Hall effects in
itinerant magnets. This scenario was later confirmed experimentally in a class of
insulating magnets including a pyrochlore ferromagnet Lu2V2O7 [4].
Reference:
[1] H. Katsura, N. Nagaosa, and A. V. Balatsky, Phys. Rev. Lett. 95, 057205 (2005).
[2] See reviews, e.g., Y. Tokura, S. Seki, and N. Nagaosa, Rep. Prog. Phys. 77,
076501 (2014).
[3] H. Katsura, N. Nagaosa, and P. A. Lee, Phys. Rev. Lett. 104, 066403 (2010).
[4] Y Onose et al., Science 329, 297 (2010).
7
Fr-P-7
Opera
Friday 13:30-14:15
When topology meets SCES
Leon Balents
Kavli Institute of Theoretical Physics, University of California, Santa Barbara, CA, 93106, USA
The role of topology seems to be growing limitlessly in condensed matter and
materials physics. Strongly correlated electrons are an enduring theme of the field,
and a source of mysteries that withstand decades of research. What happens when an
irresistible force meets an immovable object? In this talk I will discuss different
manifestations of topology in strongly correlated electron systems, covering examples
from both materials phenomenology and fundamental theory.
8
Parallel Sessions
(Venue: Mengminwei Bld.)
9
Mo-S1-1
Mengminwei R225
Monday 10:30-11:00
Interplay of Pair-Density Wave & Charge-Density Wave States with
d-wave Superconductivity in Underdoped Cuprates
J.C. Séamus Davis1,2,3 M. H. Hamidian1,4, S. D. Edkins1,3, K. Fujita2, & A. P.
Mackenzie3,5
1. LASSP, Department of Physics, Cornell University, Ithaca, NY 14853, USA
2. CMPMS Department, Brookhaven National Laboratory, Upton, NY 11973, USA
3. School of Physics and Astron., University of St. Andrews, Fife KY16 9SS, Scotland.
4. Department of Physics, Harvard University, Cambridge, MA 02138, USA
5. Max-Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany.
A central issue of copper-oxide high temperature superconductivity research is to
understand the nature of the pseudogap phase and its relationship to both the
superconductivity and the charge order. Our sub-lattice phase-resolved electronic
structure visualization within each CuO2 unit-cell [1] revealed that the cuprate charge
density wave (CDW) state is unique in that it exhibits a d-symmetry form factor [2,3].
We also find that the characteristic energy gap of this d-symmetry CDW state is
actually the pseudogap energy [4].
The existence and symmetry of this exotic CDW state has motivated contemporary
microscopic theories in which the pseudogap phase must also contain a spatially
modulating Cooper-pair density wave (PDW) state. In theory, the PDW state is akin
to the famous FFLO state of spatially modulated superconductivity, but generated by
strong correlations instead of high magnetic fields. However, since the original
theoretical proposals in 1964, no FFLO (or PDW) state has ever been observed.
To search for a cuprate PDW, we use scanned Josephson tunneling microscopy
(SJTM) to image Cooper-pair tunneling from a d-wave superconducting STM tip at
millikelvin temperatures to the Cooper-pair condensate of underdoped Bi2Sr2CaCu2O8.
The resulting images of the Cooper-pair condensate show clear pair density
modulations oriented along the Cu-O bond directions. Fourier analysis reveals the
direct signature of a Cooper-pair density wave at wavevectors
QP≈(0.25,0)2π/a0;(0,0.25)2π/a0; the amplitude of these modulations is ~ 5% of the
background condensate density and their form factor exhibits s/s‟-symmetry [5].
We review the implications from the discovery of a PDW state in cuprates, and the
observed interplay of CDW, PDW and dSC, for the microscopic theory of the
pseudogap phase.
References
[1] Nature 466, 347 (2010).
[2] PNAS 111, E3026 (2014).
[3] Science 344, 612 (2014).
[4] Nat.Phys. 12, 150 (2015).
[5] Nature in press; arXiv:1511.08124 (2016)
10
Mo-S1-2
Mengminwei R225
Monday 11:00-11:30
Quantitative Determination of the Pairing Interactions for High
Temperature Superconductivity in Cuprates
Xingjiang Zhou*
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, CAS, Beijing
100190, China
Email: *[email protected]
A profound problem in modern condensed matter physics is discovering and
understanding the nature of the fluctuations and their coupling to fermions in cuprates
which lead to high temperature superconductivity and the invariably associated
strange metal state. Here we report the quantitative determination of the normal and
pairing self-energies, made possible by laser-based angle-resolved photoemission
measurements with unprecedented accuracy and stability. Through a precise inversion
procedure, both the effective interactions in the attractive d-wave symmetry and the
repulsive part in the full symmetry are determined. Besides finding the pairing
self-energy and the attractive interactions for the first time, these results expose a
central paradox of the high Tc problem: how the same frequency independent
fluctuations can dominantly scatter at angles ±π/2 in the attractive channel as well as
lead to angle-independent repulsive scattering. The experimental results are compared
with the available theoretical calculations based on antiferromagnetic fluctuations,
Hubbard model and the quantum-critical fluctuations of loop-current order.
*This work is done in collaboration with Jin Mo Bok, Jong Ju Bae, Han-Yong Choi,
Chandra M. Varma, Wentao Zhang, Junfeng He, Yuxiao Zhang and Li Yu
Reference
[1]. J. M. Bok et al., arXiv : 1601.02493, to appear in Science Advances, March 4,
2016.
11
Mo-S1-3
Mengminwei R225
Monday 11:30-12:00
Interplay between superconductivity and CDW in Cuprates and
dichalcogenides form IXS
M. Le Tacon1, S.M. Souliou1,2, H. Gretarsson1, A. Bosak2, M. Leroux3, P. Rodière3,
I.Errea4, M.Calandra5, B.Keimer1
1. Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart,
Germany
2. European Synchrotron Radiation Facility, Grenoble, France
3. UniversitéGrenoble Alpes, CNRS, Institut Néel, F-38000 Grenoble, France
4. IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain
5. IMPMC, UMR CNRS 7590, Univ. Paris 06, 75005 Paris, France
I will focus on the interplay between superconductivity and charge density waves in
superconducting cuprates and dichalcogenides.
High resolution inelastic x-ray scattering was used to observe of a
quasi-elastic„central peak‟ in underdoped YBa2Cu3O6.6, demonstrating the static
nature of the CDW correlations, attributed to the pining of CDW nanodomains on
defects (1). Low energy phonons also exhibit anomalously large superconductivity
induced renormalizations close to the CDW ordering wave vector, providing new
insights regarding the long-standing debate of the role of the electron-phonon
interaction, a major factor influencing the competition between collective instabilities
in correlated-electron materials. Relationship to the well-known anomalies in reported
in the higher energy phonon branches will be discussed. Finally, dependence of these
effects with pressure will be reported.
Pressure has also been used to tune the ground state of a less correlated
material,2H-NbSe2. There a fast hardening of the soft phonon mode with pressure is
observed,much faster than predicted by calculations carried out at the harmonic level.
Inclusion of the full anharmonic potential in the calculation yields an excellent
agreement with the experimental data, and further allows demonstrating the major
role of the electron-phonon interaction in the superconducting mechanism (2, 3).
Reference:
[1]. M. Le Tacon et al., Inelastic X-ray scattering in YBa2Cu3O6.6 reveals giant
phonon anomalies and elastic central peak due to charge-density-wave formation.
Nat. Phys. 10, 52-58 (2014).
[2].M. Leroux et al., Strong anharmonicity induces quantum melting of charge density
wave in 2H-NbSe2 under pressure. Phys. Rev. B 92, 140303 (2015).
[3].M. Leroux et al., Anharmonic suppression of charge density waves in 2H-NbS2
Phys. Rev. B 86, 155125 (2012).
12
Mo-S1-4
Mengminwei R225
Monday 12:00-12:15
Signature of the pseudogap critical point in cuprate superconductors
S. Badoux1, S.A.A. Afshar1, B. Michon1, A. Ouellet1, G. Grissonnanche1, S. Fortier1,
D.LeBoeuf2, W. Tabis3,4, F. Laliberté3, B. Vignolle3, D. Vignolles3, J. Béard3, T.P.
Croft5, C. Lester5, S.M. Hayden5, H. Takagi6, K. Yamada7, D. Graf8, D.A. Bonn9,10,
W.N. Hardy9,10, R. Liang9,10, N. Doiron-Leyraud1, C. Proust3,10, and L.Taillefer1,10
1. Département de physique & RQMP, Universitéde Sherbrooke, Sherbrooke, Québec J1K
2R1, Canada
2. Laboratoire National des Champs Magnétiques Intenses, (CNRS-INSA-UJF-UPS),
Grenoble 38042, France
3. Laboratoire National des Champs Magnétiques Intenses (CNRS, INSA, UJF, UPS),
Toulouse 31400, France
4. AGH University of Science and Technology, Faculty of Physics and Applied Computer
Science, 30-059 Krakow, Poland
5. H. H. Wills Physics Laboratory, University of Bristol, Bristol, BS8 1TL, United
Kingdom
6. Department of Physics, University of Tokyo, Tokyo, Japan
7. Institute of Materials Structure Science, High Energy Accelerator Research Organization
& The Graduate University for Advanced Studies, Oho, Tsukuba 305-0801, Japan
8. National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
9. Department of Physics and Astronomy, University of British Columbia, Vancouver,
British Columbia V6T1Z1, Canada.
10. Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
Since the discovery of the cuprates 30 years ago, the mechanism of the
superconductivity in these materials is still an open question. The phase diagram of
hole-doped cuprates is composed of different phases. The link between these phases is
not yet clear. The most studied and the less understood of these phases is the
pseudogap phase. In order to study this phase at low temperature, high magnetic fields
are required to suppress superconductivity. I will present measurements of the Hall
and Seebeck coefficients on two cuprate materials, YBCO [1] and LSCO [2],
performed in magnetic fields large enough to suppress superconductivity at low
temperature. We arrive at two main findings. First, with decreased doping, the
pseudogap critical doping p* occurs well before the onset of the charge-density-wave
order that develops in these materials. So the two phenomena are separate. Secondly,
the carrier density n is observed to drop sharply at p*, going from n = 1+ p above p*
to n = p below p*. This signature imposes strong constraints on the possible nature of
the pseudogap phase.
Reference:
[1] S. Badoux et al, arXiv: 1511.08162 (2015)
[2] S. Badoux et al, arXiv: 1512.00292 (2015)
13
Mo-S2-1
Mengminwei R139
Monday 10:30-11:00
Spin-spin correlations, spin-orbit/Hund’s coupling, and
metal-insulator transition in Ca2RuO4
Yuki Utsumi1, Deepa Kasinathan1, Stefano Agrestini1, Kyung-Tae Ko1, Maurits W.
Haverkort1,Alexander C. Komarek1, Yen-Fa Liao2, Ku-Ding Tsuei2, Daniel
Khomskii3, Liu Hao Tjeng1
1.
Max-Planck-Institut für Chemiche Physik fester Stoffe, Nöthnitzer Strasse 40, 01187 Dresden,
Germany
2. National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30077,
Taiwan
3. II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
Single layered perovskite Ca2RuO4 has an independent metal-insulator and
magnetic phase transition as a function of temperature. Accompanied by crystal
structure distortion, Ca2RuO4 changes from paramagnetic metal to a paramagnetic
insulator below ~ 375 K, transforming later to an antiferromagnetic insulator ~ 110 K.
We performed bulk sensitive hard x-ray photoelectron spectroscopy and report the
temperature dependent evolution of the valence band spectra across all the three
phases in Ca2RuO4. Opening of a gap is observed in the valence band spectra across
the metal-insulator transition (MIT), but with an atypically huge transfer of spectral
weight. We discover another, hitherto unreported large spectral weight transfer and an
additional enhancement of the gap across the magnetic transition. X-ray absorption
spectroscopy measurements reveal a strong temperature dependence of the orbital
occupation both below MIT and below the magnetic transition, though the latter is not
enough to explain the enormous spectral weight transfer observed in the valence band
spectra. Using a two-site three-orbital Hubbard model, we demonstrate the relevance
of the inter-site spin-spin correlations in comprehending the spectral weight transfer
and gap enhancement. An ubiquitous well resolved two-peak structure close to the
Fermi level is present at all temperatures, which can be linked to the Ru 4d t 2g orbitals
that are split as a result of the Hund's coupling between the opposite spin channels.
14
Mo-S2-2
Mengminwei R139
Monday 11:00-11:30
Critical Slowing Down of the Charge Carrier Dynamics at the Mott
Metal-Insulator Transition in Molecular Conductors
B. Hartmann1, D. Zielke1, J. Polzin1, T. Sasaki2, Jens Müller1
1. Institute of Physics, Goethe-University Frankfurt, Frankfurt(M), Germany
2. Institute for Materials Research, Tohoku University, Sendai, Japan
The unique possibilities of fine-tuning their physical properties in the vicinity of the
Mott metal-insulator transition (MIT) [1] make the quasi-two-dimensional organic
charge-transfer salts κ-(BEDT-TTF)2X unprecedented model systems for studying the
fundamentals of electron-electron correlations and the coupling between charge, spin
and lattice degrees of freedom in reduced dimensions. Here, the critical properties and
the universality class of the Mott transition is controversially debated, and information
on the low-frequency dynamical properties of the correlated electrons is rather limited.
In the past years, we have introduced fluctuation (noise) spectroscopy as a powerful
new tool for studying the slow dynamics of charge carriers in these materials [2].
From such measurements, we (i) have been able to extract spectroscopic information
on the coupling of charge carriers to the vibrational degrees of freedom of the crystal
lattice, and (ii) have observed a pronounced and sudden slowing down of the carrier
dynamics in the vicinity of the finite-temperature critical endpoint of the Mott
transition. Recently, we have tuned a system across the Mott MIT and find that the
low-frequency resistance fluctuations show a dramatic enhancement and divergent
behavior when tuning the sample closer to the critical point, accompanied by a strong
shift of spectral weight to low frequencies and the onset of non-Gaussian behavior [3].
This indicates the critical slowing down of the order-parameter (doublon density)
fluctuations and suggests a collective dynamics of the correlated electrons, which may
be universal features of any MIT, as will be discussed in this contribution based on
the comparison of our results to other MITs of different origin and dimensionality.
Furthermore, in this talk we discuss the effect of randomness in the electronic system
introduced either by controlling the intrinsic glass-like molecular ordering of the
BEDT-TTF molecules‟ terminal ethylene groups [4] or by controlled (extrinsic) X-ray
irradiation of the crystals [5].
References:
[1] B. Hartmann et al., PRL 114, 216403 (2015).
[2] J. Müller, ChemPhysChem 12, 1222 – 1245 (2011).
[3] B. Hartmann et al., PRB 90, 195150 (2014).
[4] J. Müller et al., NJP 17, 083057 (2015).
[5] T. Sasaki, Crystals 2, 374 – 392 (2012).
15
Mo-S2-3
Mengminwei R139
Monday 11:30-12:00
Heavy electrons at the Mott transition in NiS2
Sven Friedemann1, Hui Chang2, Monica Gamza3, William Coniglio4, Stan Tozer5,
Malte Grosche2
1. HH Wills Laboratory, University of Bristol, Bristol,UK
2. Cavendish Laboratory, University of Cambridge, Cambridge, UK
3. Jeremiah Horrocks Institute for Mathematics, University of Central Lancashire, UK
4. National High Magnetic Field Laboratory, FL, USA
The Mott transition at half-filling is controlled by the ratio of Coulomb repulsion
and kinetic energy. For this case, Luttinger theorem dictates the electrons to localize
via a divergence of the effective mass as predicted by Brinkman and Rice [1] while
further theoretical work suggests variations to this expectation [2]. Despite this long
history of the Brinkman-Rice prediction it challenges experimental testing in
transition metal compounds. We were able – for the first time – to detect the Fermi
surface in a single sample tuned through the Mott transition with high-pressure [3].
Using novel quantum oscillation techniques we find the large Fermi surface and a
strong mass enhancement in proximity to the Mott transition in NiS2. Our results
confirm the central expectations of the Brinkman-Rice scenario of a correlation driven
localization and open routes to study the effects of electron localization in more detail
in order to test detailed theoretical predictions.
Reference:
[1] W. F. Brinkman and T. M. Rice, Phys. Rev. B 2, 4302 (1970).
[2] A. Georges, et al., Rev. Mod. Phys. 68, 13 (1996).
[3] S. Friedemann, et al. , arXiv:1509.00397 [cond-Mat.str-El] (2015).
16
Mo-S2-4
Mengminwei R139
Monday 12:00-12:15
Pressure induced insulator to metal transition in neutral radical
FBBO
D. Tian1, S.R. Julian1, S. Winter2, A. Mailman3, R. T. Oakley4
1. Department of Physics, University of Toronto, Toronto ON, Canada
2. Goethe University, Frankfurt, Germany
3. University of Jyvaskyla, Finland
4. Department of Chemistry, University of Waterloo, Waterloo ON, Canada
We have measured resistivity vs. temperature and pressure on the fluoro-substituted
oxobenzene-bridged bisdithiazolyl radical, FBBO. This is a layered, single component
organic compound that is a Mott insulator at ambient pressure, due to the singly
occupied molecular orbitals and an intrinsically high inter-molecular charge transfer
energy barrier. Previous room temperature infrared absorption and conductivity
measurements suggest that the charge gap of 0.1eV closes and the sample may
become metallic at pressures above 3GPa. We report direct transport measurements
under various pressures on powder samples of FBBO down to low temperature,
measured in an anvil pressure cell. These show the first successful metallization of a
neutral organic radical, with a resistivity at 6.2 GPa that is consistent with Fermi
liquid theory. In the range between 3.0 and 5.0 GPa, there is evidence of a magnetic
phase at low temperature, suggesting that the metal-insulator quantum critical point
may have a concomitant magnetic quantum critical point.
Reference:
[1] D. Tian et al., Journal of the American Chemical Society 137 (2015) 14136.
17
Mo-S3-1
Mengminwei R225
Monday 16:00-16:30
Multiband superconductivity and nodal superconducting gap in the
newly discovered superconductor β-FeS
Jie Xing, Hai Lin, Sheng Li, Yufeng Li, Jianzhong Liu, Xiyu Zhu, Huan Yang and
Hai-Hu Wen
National Laboratory of Solid State Microstructures and Department of Physics, Collaborative
Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
Recently, superconductivity has been discovered in the β -FeS phase which has an
isostructure of FeSe superconductor. Up to now, it is completely open for this newly
discovered new superconductor concerning physical properties. It is also very curious
to know whether a high temperature superconducting phase can be achieved in the
FeS-based systems. We have successfully synthesized the β -FeS superconductor and
have measured many transport and thermal dynamic properties. The
superconductivity appears at about 4.5 K, as revealed by both resistive and
magnetization measurements. It is found that the upper critical field is relatively low,
with however a rather large anisotropy γ =[dHc2ab / dT ] /[dHc2c / dT ]Tc~6. A huge
magnetoresistivity (300% at 9T and 5K, H||c-axis) together with a non-linear behavior
of Hall resistivity vs. external field H are observed. The Hall coefficient shows a
negative sign with non-monotonic temperature dependence. The non-linear Hall effect
and huge magnetoresistivity indicate a multi-band superconductivity in the new
superconductor FeS1.
Low temperature specific heat down to 0.4K has been measured in the newly
discovered superconductor β -FeS superconductor. It is found that the low
temperature electronic specific heat Ce/T can be fitted to a power law like
temperature dependence in the low temperature limit, but fails to be described by an
exponential relation as expected by an s-wave gap. Detailed fitting to the data with
different gap structures find that a model with two nodal gaps can fit the data. Under a
magnetic field, the field induced specific heat follows the Volovik relation △ γ =AH0.5
quite well, indicating the presence of nodal gap(s) in this material2.
References:
[1] Hai Lin, Yufeng Li, Jie Xing, Jianzhong Liu, Xiyu Zhu, Huan Yang, Hai-Hu Wen,
arXiv 1511.08716.
[2] Jie Xing, Hai Lin, Yufeng Li, Sheng Li, Xiyu Zhu, Huan Yang, Hai-Hu Wen,
arXiv 1512.04074.
18
Mo-S3-2
Mengminwei R225
Monday 16:30-16:45
Stripe-order antiferromagnetism without orbital ordering in FeSe
under pressure
Weiqiang Yu, P. Wang, Y. Cui, W. Song, T. Li, R. Yu, S. Sun, H. Lei
Department of Physics, Renmin University of China, Beijing, 100872
The magnetic structure and the spin fluctuations are believed essential for
understanding high-temperature superconductivity in the cuprate and the iron-based
superconductors. In bulk FeSe, a paramagnetic quantum nematic state with orbital
ordering was seen at the ambient pressure; with increasing pressure, the orbital
ordering is suppressed, whereas the long-range order antiferromagnetism and
high-temperature superconductivity emerges. This is in sharp contrast to iron
pnictides, where the orbital ordering always sets in above a stripe-order magnetism.
This leads to heated interests in the nature of magnetism and superconductivity of
FeSe.
Here we report a high-pressure 77Se NMR study on FeSe single crystals with
temperaturedown to 50 mK. We established the microscopic evidence for the
suppression of the orbital ordering at P ~ 2.5 GPa. Strikingly, a novel stripe
antiferromagnetic order is still observed, where the Fe moments are not locked along
any principal axis of crystal. This state breaks C4 symmetry, and the transition
becomes a first-order type, when the orbital ordering is absent. At high temperatures,
the stripe-type spin fluctuations, evidenced by the 1/77T1T, persists and increases with
pressure. Our data indicates that the stripe-type magnetism is universal and is not
caused by the orbital ordering, which provides vital ingredients for the understanding
the pairing mechanism in iron chalcogenides and other iron-based superconductors.
19
Mo-S3-3
Mengminwei R225
Monday 16:45-17:00
Tuning orbital-selective correlations in the superconducting
Rb0.75Fe1.6Se2-zSz
Zhe Wang1, V. Tsurkan1,2, M. Schmidt1, A. Loidl1, and J. Deisenhofer1
1. Experimental Physics V, Center for Electronic Correlations and Magnetism, Institute of
Physics, University of Augsburg, D-86135 Augsburg, Germany
2. Institute of Applied Physics, Academy of Sciences of Moldova, MD-2028 Chisinau,
Republic of Moldova
We report on terahertz time-domain spectroscopy on superconducting and metallic
iron chalcogenides Rb0.75Fe1.6Se2-zSz [1]. The superconducting transition is reduced
from Tc = 32 K (z = 0) to 22 K (z = 1.0), and finally suppressed (z = 1.4) by
isoelectronic substitution of selenium with sulfur. Dielectric constant and optical
conductivity exhibit a metal-to-insulator transition associated with an orbital-selective
Mott phase [2]. This orbital-selective Mott transition appears at higher temperatures
Tmet with increasing sulfur contents [1], identifying sulfur substitution as an efficient
parameter to tune orbital-dependent correlation effects in iron-chalcogenide
superconductors. The reduced correlation strength of the dxy charge carriers may also
account for the suppression of the pseudogap-like feature between Tc and Tmet that
was observed for z = 0 [2].
Reference:
[1] Zhe Wang et al., arXiv: 1506.04614 (2015).
[2] Zhe Wang et al., Nature Communications 5, 3202 (2014).
20
Mo-S3-4
Mengminwei R225
Monday 17:00-17:15
Nematic orders in iron superconductors viewed by a renormalization
group approach
Carsten Honerkamp
Institute for Theoretical Solid State Physics, RWTH Aachen University, Germany
We present new results on a simple three-orbital model for iron superconductors,
obtained in a renormalization group approach with orbitally resolved interactions. We
that show that nematic orbital ordering occurs very naturally in different forms as
competitor but also concomitant ordering tendency to the more conventional
antiferromagnetic ordering and spin-fluctuation-induced pairing at low energies. We
discuss physical conditions under which nematicity is favored.
21
Mo-S3-5
Mengminwei R225
Monday 17:15-17:30
Anomalous Scaling Relations and Pairing Mechanism of the
Fe-based Superconductors
Yunkyu Bang1 and G. R. Stewart2
1. Department of Physics, Chonnam National University, Kwangju, South Korea
2. Physics Department, University of Florida, Gainesville, FL 32611-8440, USA
Two anomalous scaling relations were observed in the Fe-based superconductors
with more than 40 compounds: (1) the specific heat (SH) jump vs. Tc, ΔC ~Tc 3 [1];
the condensation energy (CE) vs Tc, ΔE ~ Tc 3.5 [2]. Because both scaling relations
are very non-BCS-like, they were taken as strong evidences for a non-BCS pairing
mechanism of Fe-based superconductors, for example, Quantum Criticality induced
superconductivity. In a series of works[3,4], we have shown that these two non-BCS
scaling relations can be simultaneously reproduced by a minimal two-band BCS
model with the S± -wave gap solution.
Our results show that these seemingly non-BCS-like scaling relations, on the
contrary to the common expectation, are strong experimental evidences that the
pairing mechanism of the Fe-based superconductors is genuinely a BCS mechanism.
Reference:
[1] S. L. Budko, N. Ni, and P. C. Canfield, Phys. Rev. B 79, 220516 (2009)
[2] J. Xing et al., Phys. Rev. B 89, 140503(R) (2014)
[3] Y. Bang and G.R. Stewart, New. J. Phys. 18, 023017 (2016)
[4] Y. Bang, arXiv:1601.01847
22
Mo-S4-1
Mengminwei R139
Monday 16:00-16:30
Pressure-induced exotic states in rare earth hexaborides
Liling Sun1,2
1.
Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese
Academy of Sciences, Beijing 100190, China
2. Collaborative Innovation Center of Quantum Matter, Beijing 100190, China
Finding the exotic phenomena in strongly correlated electron systems (SCESs)
and understanding the corresponding microphysics have long been the research
frontiers of condensed matter physics. The remarkable examples for the intriguing
phenomena discovered in the past years include unconventional superconductivity,
heavy Fermion behaviors, giant magneto-resistance and so on. A fascinating type of
rare earth exaborides RB6 (R= Sm, Yb), with unusual high pressure behaviors,
typically belong to this category. The new interests for the investigation on the RB6
were motivated by the discovery of the coexistence of nontrivial metallic surface
state and insulating bulk state in SmB6 by theoretical calculations and many
experimental measurements. This significant progress encourages people to revisit
the RB6 with an attempt to establish a new physics that links the SCES and the
topological insulator (TI). It is well known that pressure has the capability in tuning
the electronic structure and modifying the ground state of solids, or even inducing a
quantum phase transition which is one of kernel issues in the studies of SCESs. In
this talk, we will describe the progress in high pressure studies on the RB 6, mainly
focusing on the phenomena of pressure-induced exotic phases in YbB6 and SmB6
and the corresponding quantum phase transitions, as well as the connections with the
valence state of the rear earth ions.
The speaker thanks collaborators Yazhou Zhou, Zhongxian Zhao, Qi Wu, Yi-feng
Yang, Qimiao Si, Rong Yu, Zachary Fisk, Priscila Ferrari Silveira Rosa, Dae-Jeong
Kim and Joe D. Thomposon.
23
Mo-S4-2
Mengminwei R139
Monday 16:30-16:45
Rotational symmetry breaking of the upper critical field of the
candidate topological superconductor SrxBi2Se3
Y. Pan1, A.M. Nikitin1, G.K. Araizi1, Y.K. Huang1, Y. Masushita2, T. Naka2 and A.
de Visser1
1.
2.
Van der Waals-Zeeman Institute, University of Amsterdam, 1098 XH Amsterdam, The
Netherlands
National Institute for Materials Science, Sengen 1-2-1, Tsukuba, Ibaraki 305-0047, Japan
Recently, it was demonstrated that Sr intercalation provides a new route to induce
superconductivity (Tc = 3 K) in the topological insulator Bi2Se3 (Liu et al., J. Am.
Chem. Soc. 37,10512, 2015). Topological superconductors are predicted to be
unconventional with mixed even and odd-parity Cooper pair states. Here we report a
remarkable property of the upper critical field, Bc2, of SrxBi2Se3. Besides the usual
anisotropy when the magnetic field is applied parallel and perpendicular to the
quintuple layers, we observe a striking two-fold anisotropy of Bc2 when the field is
rotated within the layers. Notably, angular dependent magnetotransport
measurements show a pronounced two-fold anisotropy with Bc2a = 7.4 T and Bc2a* =
2.3 T for x = 0.15 at T/Tc = 0.1, where a and a* are two orthogonal directions in the
trigonal basal-plane (see Figure 1). The large ratio Bc2a/Bc2a*= 3.2 cannot be
explained with the Ginzburg-Landau anisotropic effective mass model or flux flow
induced by the Lorentz force. The rotational symmetry breaking of Bc2 possibly
signals a polarized spin-triplet state (△4 pairing), or might have a structural nature,
such as preferential ordering of Sr atoms.
Figure 1: Angular variation of the upper critical field of Sr0.15Bi2Se3 at T=0.3 K and 2
K, whereθis the direction of the magnetic field in the trigonal basal plane.
24
Mo-S4-3
Mengminwei R139
Monday 16:45-17:00
Ultrafast Charge and Spin Dynamics in the Topological
Insulators
M. C. Wang1,2, S. Qiao3,4, Z. Jiang5, S. N. Luo1,2, and J. Qi1,2
1. The Peac Institute of Multiscale Sciences, Chengdu, Sichuan, China
Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest
Jiaotong University, Chengdu, Sichuan, China
3. Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences,
Shanghai, China
4. School of Physical Science and Technology, ShanghaiTech University, Shanghai, China
5. School of Physics, Georgia Institute of Technology, Atlanta, Georgia, USA
2.
Topological insulators (TIs) are characterized by an unusual electronic structure
exhibiting both insulating bulk and robust metallic surface states (SSs). This unique
electronic structure combining external light excitation leads to TIs a great promise
for opto-spintronics and ultrafast spintronics applications. Therefore, understanding
the charge and spin dynamics in TIs becomes quite essential. Here, using ultrafast
pump-probe optical spectroscopy, related studies in a prototypical TI Bi2Se3 has been
discussed in detail. Similar investigation and results, in principle, can be extended to
other TIs. In specific, ultrafast manipulation of coherent spin states in the Kondo TI
SmB6 has been proposed.
Reference:
[1] M. C. Wang, S. Qiao, Z. Jiang, S. N. Luo, and J. Qi, PRL 116, 036601 (2016).
25
Mo-S4-4
Mengminwei R139
Monday 17:00-17:15
CeRu4Sn6: Failed or topological Kondo insulator?
J. Hänel, A. Sidorenko, L. Prochaska, S. Dzsaber, M. Taupin, V. Martelli, J. Larrea
J., A. Prokofiev, and S. Paschen
Institute of Solid State Physics, Vienna University of Technology, Vienna, Austria
The tetragonal compound CeRu4Sn6 appears to show signatures of both a failed
or nodal Kondo insulator [1] and of nontrivial topology [2]. To shine further light on
these seemingly conflicting findings we have measured a comprehensive set of
thermodynamic, spectroscopic, and transport data, both on bulk and mesostructured
single crystals. These will be presented and discussed in the context of recent results
on other Kondo insulators.
We gratefully acknowledge financial support from the Austrian Science Fund
(FWF projects W1243-N16, I623-N16, and I2535-N27) and the US Army Research
Laboratory (W911NF-14-1-0496).
References:
[1] Anisotropic optical conductivity of the putative Kondo insulator CeRu4Sn6, V.
Guritanu, P. Wissgott, T. Weig, H. Winkler, J. Sichelschmidt, M. Scheffler, A.
Prokofiev, S. Kimura, T. Iizuka, A. M. Strydom, M. Dressel, F. Steglich, K.
Held, S. Paschen, Phys. Rev. B 87, 115129 (2013).
[2] CeRu4Sn6: a strongly correlated material with nontrivial topology , M.
Sundermann, F. Strigari, T. Willers, H. Winkler, A. Prokofiev, J. M. Ablett, J.-P.
Rueff, D. Schmitz, E. Weschke, M. Moretti Sala, A. Al-Zein, A. Tanaka, M. W.
Haverkort, D. Kasinathan, L. H. Tjeng, S. Paschen, A. Severing, Sci. Rep. 5,
17937 (2015).
26
Mo-S4-5
Mengminwei R139
Monday 17:15-17:30
Topological phase in a bilayer honeycomb lattice
Tsuneya Yoshida1 and Norio Kawakami2
1
Condensed Matter Theory Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan
2
Department of Physics, Kyoto University, Kyoto 606-8502, Japan
Recently, correlation effects on topological insulators attract much interest
because electron correlations under the nontrivial condition can induce exotic
phenomena. One of the important effects is that correlation effects can change
properties of the gapless edge modes. In particular, it became clear that the
correlations can gap out edge modes in non-interacting topological insulators
without symmetry breaking[1,2]. Unfortunately, however, this issue has not been
sufficiently explored yet. Especially there are few systematic analyses for the bulk
and the edges.
In order to address this issue, we study a correlated bilayer honeycomb lattice
model[3] by using real-space dynamical mean field theory with continuous-time
quantum Monte Carlo method. Our analysis elucidates that the topological
invariant takes a nontrivial value even when the gapless edge modes are destroyed.
In the presentation, we also discuss finite temperature effects which are relevant for
experiments[4].
Reference:
[1] Y.-M. Lu and A. Vishwanath , Phys. Rev. B 86, 125119 (2012); M. Levin and A.
Stern, Phys. Rev. B 86, 115131 (2012); T. Yoshida, et al., Phys. Rev. B 92, 245122
(2015) etc.
[2] T. Yoshida et al., Phys. Rev. Lett. 112, 196404 (2014).
[3] K. Slagleet al., Phys. Rev. B 91, 115121 (2015); Y.-Y. Heet al.,
arXiv:1512.02080 (2015).
[4] T. Yoshida and N. Kawakami in preparation.
27
Tu-S5-1
Mengminwei R225
Tuesday 8:30-9:00
Magnetic Exchange Interactions and ANNNI Physics in CeRhIn5
M. Janoschek1, D. Fobes1, Pinaki Das1, F. Ronning1, S.-Z. Lin1, C. D. Batista1, N. J.
Ghimire1, E. D. Bauer1, J. D. Thompson1, L. Harringer2, G. Ehlers3
2.
1. Los Alamos National Laboratory, Los Alamos, NM, USA
National Institute of Standards and Technology, Gaithersburg, MD, USA
3. Oak Ridge National Laboratory, Oak Ridge, TN, USA
The phase diagram of CeRhIn5 is in many ways a prototypical example of a
heavy fermion superconductor; its antiferromagnet state can be tuned to a quantum
critical point (QCP) via the application of pressure, around which unconventional
superconductivity emerges. Closer inspection reveals unusual behavior however;
the interplay between magnetism and unconventional superconductivity is highly
complex, and the observed electrical transport behavior, as well as a significant
change of the Fermi surface at the QCP are not in agreement with the prototypical
spin-density-wave-type scenario. Our recent high-resolution neutron spectroscopy
at ambient pressure and zero magnetic field reveals clear spin wave excitations that
can be explained with a simple frustrated J1-J2 model based on localized Ce 4f
electrons. This result is in agreement with a small Fermi surface in the
antiferromagnetic state. More recently, we have also measured the spin wave
spectrum with a magnetic field applied in the tetragonal basal plane [2]. Here we
show that the addition of magnetic anisotropy and Zeeman terms to our anisotropic
next-nearest neighbor Ising (ANNNI) model Hamiltonian not only quantitatively
fits the observed spin wave spectrum, but is also able to reproduce the
experimentally established magnetic field vs. temperature phase diagram. Finally,
the ANNNI model predicts that the magnetic propagation vector should change
logarithmically as a function of temperature across the high-field
incommensurate-to-commensurate phase boundary, in agreement with our latest
high-resolution neutron diffraction results. Our work not only determines the
magnetic exchange interactions of CeRhIn5 for the first time and paves the way to a
quantitative understanding of the rich low-temperature phase diagram of the
prominent CeTIn5 (T = Co, Rh, Ir) class of heavy fermion materials, but also
identifies CeRhIn5 as the first heavy fermion material that exhibits ANNNI physics.
Reference:
[1] P. Das, S.-Z. Lin, N. J. Ghimire, K. Huang, F. Ronning, E. D. Bauer, J. D.
Thompson, C. D. Batista, G. Ehlers, M. Janoschek, Phys. Rev. Lett. 113, 246403
(2014).
[2] D. Fobes, S.-Z. Lin, N.J. Ghimire, P. Das, F. Ronning, E.D. Bauer, J.D.
Thompson, C.D. Batista, L. Harringer, G. Ehlers, and M. Janoschek, in preparation.
28
Tu-S5-2
Mengminwei R225
Tuesday 9:00-9:30
Fermi surface reconstruction and quantum criticality in CeRhIn5
L. Jiao1,2, Y. Chen1, Y. Kohama2, David Graf3, J. Singleton2, M. Jaime2, E. D. Bauer2,
J. D. Thompson2, F. Steglich1,2, and H. Q. Yuan1
1.
Center for Correlated Matter and Department of Physics, Zhejiang University, China
2. Max-Planck Institute for Chemical Physics of Solids, Germany
3. Los Alamos National Laboratory, USA,
4. National High Magnetic Field Laboratory, Florida State University, USA
The long range antiferromagnetic (AFM) order in the heavy fermion metal CeRhIn5
can be eventually suppressed by using various non-thermal tuning parameters. A
dramatic change of Fermi surface was previously reported at the pressure-induced
quantum critical point which has been proposed to support local quantum critical
point (QCP) [1]. Recently, we show that its AFM order can be also suppressed by
applying a strong magnetic field of Bc0  50T. A field-induced reconstruction of the
Fermi surface is observed around B* = 30T, prior to the AFM QCP [2]. Our results
indicate the existence of multiple quantum phase transitions in CeRhIn5 [2]. In this
presentation, we will report our measurements of various physical properties under
strong magnetic field for CeRhIn5, with an emphasis on probing the nature of the
Fermi surface reconstruction at B* = 30T.
Reference:
[1] H. Shishido, R. Settai, H. Harima, and Y. Onuki, JPSJ 74, 1103 (2005).
[2] L. Jiao et al., PNAS 112, 673 (2015)
29
Tu-S5-3
Mengminwei R225
Tuesday 9:30-9:45
Field-Induced Lifshitz Transition without Metamagnetism in CeIrIn5
D. Aoki1,2, G. Seyfarth3, A. Pourret2, A. Gourgout2, A. McCollam4, J. A. N. Bruin4, Y.
Krupko3, I. Sheikin3
1.
Institute for Materials Research, Tohoku University, Oarai, Ibaraki, Japan
2. CEA, INAC-SPSMS, UGA, Grenoble, France
3. Laboratoire National des Champs Magnéetiques Intenses (LNCMI-EMFL), CNRS, UGA,
Grenoble, France
4. High Field Magnet Laboratory (HFML-EMFL), Radboud University, Nijmegen, The
Netherlands
We report high magnetic field measurements of magnetic torque, thermoelectric
power, magnetization, and the de Haas–van Alphen effect in CeIrIn5 across 28 T,
where an unusual metamagnetic transition was suggested in previous studies [1, 2].
The thermoelectric power displays two maxima at 28 and 32 T. Above 28 T, a new,
low de Haas–van Alphen frequency with a strongly enhanced effective mass
emerges, while the highest frequency observed at low field disappears entirely.
These observations are most naturally accounted for by a continuous field-induced
Lifshitz transition. However, longitudinal magnetization does not show any
anomaly up to 33 T, thus ruling out a metamagnetic transition at 28 T [3].
References:
[1] E. C. Palm et al., Physica B 329-333, 587 (2003)
[2] C. Capan et al., Phys. Rev. B 80, 094518 (2009)
[3] D. Aoki et al., Phys. Rev. Lett. 116, 037202 (2016)
30
Tu-S5-4
Mengminwei R225
Tuesday 9:45-10:00
Discovery of a magnetically-driven quantum critical point inside a
superconducting phase separating two spin-density waves
D. G. Mazzone1, S. Raymond2, J. L. Gavilano1, E. Ressouche2, C. Niedermayer1, J.
O. Birk1, O. Bachir2, G. Lapertot2, M. Kenzelmann3
1.
3.
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen PSI,
Switzerland
2. SPSMS, UMR-E 9001, CEA-INAC/UJF-Grenoble 1, 38054 Grenoble, France
Laboratory for Scientific Developments and Novel Materials, Paul Scherrer Institut, 5232
Villigen PSI, Switzerland
CeCoIn5 is a heavy-fermion (HF), Pauli limited, d-wave superconductor on the
border of a magnetically-driven quantum critical point (QCP). The system features
an additional field-induced phase, called Q-phase, in form of an amplitude
modulated spin-density wave (SDW) at very low temperatures and very high
magnetic fields [1]. The microscopic theory of this multi-component ground state is
still under discussion and has only recently been further clarified suggesting the
emergence of a spin-triplet superconducting component [2].
The substitution of Nd on the Ce by five percent gives rise to long-range order
magnetism inside the superconducting phase already at zero field [3]. Interestingly,
neutron diffraction results unraveled a propagation vector similar to the one of the
Q-phase in CeCoIn5 [4]. Our results show that this low-field SDW can be suppressed
by a magnetic field inside the superconducting phase. At higher fields, we observe a
second SDW phase with nearly identical wave-vector. At very low temperature the
two SDW appear to be separated by a QCP. We will discuss possible scenarios that
lead to the observed quantum phase transition, and discuss its implications for the
microscopic interpretation of the Q-phase in CeCoIn5.
Reference:
[1] M. Kenzelmann et al., Science 321, 1652 (2008)
[2] S. Gerber et al., Nature Physics 10, 126 (2014)
[3] R. Hu et al., PRB 77, 165129 (2008)
[4] S. Raymond et al., J. Phys. Soc. Jpn. 83, 13707 (2014)
31
Tu-S6-1
Mengminwei R139
Tuesday 8:30-9:00
Interaction effects in Weyl and Dirac fermions
Naoto Nagaosa1,2
1. RIKEN Center for Emergent Matter Science (CEMS)
2. Department of Applied Physics, The University of Tokyo
Relativistic Weyl and Dirac fermions in solids are the focus of recent intensive
researches. Berry phase associated with these structures in momentum space leads to
variety of novel transport properties such as the anomalous Hall effect and
magneto-chiral effect. Now the important issue is the role of electron-electron
interaction there.
In this talk, I will describe some of our recent works on this issue including, (i)
generalization of Weyl and Dirac fermions with anisotropic dispersions, (ii)
long-range Coulomb interaction effect and non-Fermi liquid, (iii) topological Mott
insulator, and (iv) the relevance to spin wave dynamics.
32
Tu-S6-2
Mengminwei R139
Tuesday 9:00-9:30
Interplay of Topology and Geometry in Fractional Quantum Hall
Liquids
Kun Yang
National High Magnetic Field Lab and Physics Department, Florida State University, Tallahassee,
FL 32306, USA
Fractional Quantum Hall Liquids (FQHL) are the ultimate strongly correlated
electron systems, and the birth place of topological phase of matter. Early theoretical
work has emphasized the universal or topological aspects of quantum Hall physics.
More recently it has become increasingly clear that there is very interesting bulk
dynamics in FQHL, associated with an internal geometrical degree of freedom, or
metric. The appropriate quantum theory of this internal dynamics is thus expected to
take the form of a “quantum gravity”, whose elementary excitations are spin-2
gravitons. After briefly reviewing the topological aspect of FQHL, I will discuss in
this talk how to couple and probe the presence of this internal geometrical degree of
freedom experimentally in the static limit [1], and detect the graviton excitation in a
spectroscopic measurement [2].
Reference:
[1] Kun Yang, Geometry of compressible and incompressible quantum Hall States:
Application to anisotropic composite-fermion liquids, Phys. Rev. B 88, 241105
(2013).
[2] Kun Yang, Acoustic Wave Absorption as a Probe of Dynamical Gravitational
Response of Fractional Quantum Hall Liquids, arXiv:1508.01424.
33
Tu-S6-3
Mengminwei R139
Tuesday 9:30-9:45
Majorana-time-reversal symmetries: a fundamental principle for
sign-problem-free quantum Monte Carlo simulations
Zi-Xiang Li, Yi-Fan Jiang, and Hong Yao*
Institute for Advanced Study, Tsinghua University, Beijing 100084, China
A fundamental open issue in physics is whether and how the fermion-sign-problem
in quantum Monte Carlo (QMC) can be solved generically. Here, we show that
Majorana-time-reversal (MTR) symmetries can provide a unifying principle to solve
the fermion-sign-problem in interacting fermionic models. By systematically
classifying Majorana-bilinear operators according to the anti-commuting MTR
symmetries they respect, we rigorously proved that there are two and only two
fundamental symmetry classes which are sign-problem-free and which we call
"Majorana-class" and "Kramers-class". All other sign-problem-free symmetry classes
have higher symmetries than these two fundamental classes. Sign-problem-free
models in the Majorana-class include interacting topological superconductors, for
which we performed sign-problem-free Majorana QMC simulations and found that
with increasing interactions the topological superconductor's helical edge states first
undergo
spontaneous
symmetry-breaking
while
the
bulk
is
still
topologically-nontrivial. Remarkably, we discovered emergent spacetime
supersymmetry (SUSY) at the edge quantum critical point.
Reference:
[1] Zi-Xiang Li, Yi-Fan Jiang, and Hong Yao, arxiv:1601.05780 (2016).
[2] Zi-Xiang Li, Yi-Fan Jiang, and Hong Yao, Phys. Rev. B 91, 241117(R) (2015);
(Editors‟ Suggestion).
34
Tu-S6-4
Mengminwei R139
Tuesday 9:45-10:00
Monopole condensation transition out of quantum spin ice
Gang Chen1,2
1
State Key Laboratory of Surface Physics, Center for Field theory and Particle Physics,
Department of Physics, Fudan University, Shanghai
2
Collaborative Innovative Center for microstructure, Fudan University, Shanghai
We study the proximate magnetic orders and the related quantum phase transition
out of quantum spin ice (QSI). We apply the electromagnetic duality of the compact
quantum electrodynamics to analyze the condensation of the magnetic monopoles for
QSI. The monopole condensation transition represents a unconventional quantum
criticality with unusual scaling laws. The magnetic monopole condensation leads to
the magnetic states that belong to the “2-in 2-out” spin ice manifold and generically
have an enlarged magnetic unit cell. We demonstrate that the antiferromagnetic state
with the ordering wavevector Q = 2Pi(001) is proximate to QSI while the
ferromagnetic state with the ordering wavevector Q = (000) is not proximate to QSI.
This implies that if there exists a direct transition from QSI to the ferromagnetic state,
the transition must be strongly first order. We apply the theory to the puzzling
experiments on two pyrochlore systems Pr2Ir2O7 and Yb2Ti2O7.
35
Tu-S7-1
Mengminwei R225
Tuesday 10:30-11:00
Neutron scattering from the Kondo Insulator SmB6*
C. Broholm1
1. Institute for Quantum Matter and Department of Physic and Astronomy, The Johns
Hopkins University, Baltimore, MD 21218, USA
A review of neutron scattering work probing the Kondo insulator SmB6 is
presented with special emphasis on assessing the topology of the underlying
renormalized band structure. [1] A 14 meV excition dominates the spectrum and is
evidence of strong electron correlations. The data supports the proposal that SmB6 is a
topological Kondo insulator. Surprising features that may relate to sample
inhomogeneity are the finite spectral width of the exciton and a substantial T-linear
specific heat term. [2]
Reference:
*Work at IQM was supported by the U.S. Department of Energy, Office of Basic
Energy Sciences, Division of Material Sciences and Engineering under Grant No.
DE-FG02-08ER46544.
[1] Phys. Rev. Lett. 114, 036401 (2015).
[2] Phys. Rev. X 4, 031012 (2014).
36
Tu-S7-2
Mengminwei R225
Tuesday 11:00-11:30
Quantum Oscillations in Kondo Insulator SmB6
G. Li1, Z. Xiang2, C. Kurdak1, Kai Sun1, J. W. Allen1, D.-J. Kim3, X. Chen2, Z. Fisk3,
Lu Li1
1． Department of Physics, University of Michigan, Ann Arbor, USA
2． University of Science and Technology of China, Hefei, Anhui, China
3． Department of Physics, University of California, Irvine, California, USA
In Kondo insulator samarium hexaboride SmB6, strong correlation and band
hybridization lead to a diverging resistance at low temperature. The resistance
divergence ends at about 3 Kelvin, a behavior recently demonstrated to arise from the
surface conductance. However, questions remain whether and where a topological
surface state exists. Quantum oscillations have not been observed to map the Fermi
surface. We solve the problem by resolving the Landau Level quantization and Fermi
surface topology using torque magnetometry. The observed angular dependence of
the Fermi surface cross section suggests two-dimensional surface states on the (101)
and (100) plane [1]. Furthermore, similar to the quantum Hall states for graphene, the
tracking of the Landau Levels in the infinite magnetic field limit points to -1/2, the
Berry phase contribution from the 2D Dirac electronic state.
Reference:
[1] Science 346, 1208 (2014)
37
Tu-S7-3
Mengminwei R225
Tuesday 11:30-12:00
Unconventional quantum oscillations in the Kondo insulator SmB6
Suchitra Sebastian1
1.
Cavendish Laboratory, University of Cambridge
I will discuss the surprising observation of quantum oscillations in the Kondo
insulator SmB6. Evidence for the bulk origin of the observed quantum oscillations
will be presented from the angular dependence and absolute size of the oscillations.
Further clues as to an unconventional origin of the quantum oscillations are suggested
from complementary experimental observations indicating itinerant low energy
excitations. Potential models will be discussed in the context of our findings.
38
Tu-S7-4
Mengminwei R225
Tuesday 12:00-12:15
Investigation of surface properties in SmB6 by scanning tunneling
microscopy
L. Jiao1, S. Rößler1, D. J. Kim2, L. H. Tjeng1, Z. Fisk2, F. Steglich1, S. Wirth1
1.
2.
Max-Planck-Institute for Chemical Physics of Solids, Dresden, Germany
Department of Physics, University of California, Irvine, California, USA
In the past few years, the concept of topological insulators has attracted great
interest in the physical society. SmB6 has been proposed as a typical topological
Kondo insulator, which possesses topologically protected nontrivial surface states
inside the bulk hybridization gap. Experimentally, the observation of many basic
properties is still controversial, which is in part due to the reconstruction/disorder of
the cleaved surfaces of SmB6. By conducting scanning tunneling microscopy and
spectroscopy, we are able to perform local measurements on well identified surfaces.
At the base temperature of 0.35 K, we observed several well-resolved states within
the hybridization gap (within about ±20 meV) on the (001) surface of SmB6 for the
first time. These states possess sharp peak-like features with a strong temperature
dependence, especially below 5 K, i.e. the temperature at which the well-known
plateau in the resistance of SmB6 sets in. However, these states are insensitive to
external magnetic fields up to 12 T. Moreover, we found the surface states are also
robust in the vicinity of randomly occurring nonmagnetic impurities. Based on our
high resolution data, we provide detailed insight into the band structure of SmB6.
39
Tu-S8-1
Mengminwei R139
Tuesday 10:30-11:00
Strong Superconducting Fluctuations leading to a Giant Phonon
Anomaly in the Pseudogap Phase of Under doped Cuprates.
T. M. Rice1
1. ETH Zurich and Brookhaven National Labs. Upton, NY USA
As the hole density decreases and the Mott insulator is approached, umklapp
scattering processes increase in importance. Analogies between the well studied
D-Mott Insulator state in Hubbard 2-leg ladders, and the underdoped cuprates shows
that these processes can gap the 2-particle spectrum and transform a superconducting
gap into an insulating pseudogap, starting at antinodal. Long range ordered
superconductivity is then confined to 4 anisotropic pockets centered on the nodal
directions. A consistent description of the break up the Fermi surface observed in
ARPES experiments follows, as proposed earlier by Yang, Rice & Zhang. The Fermi
surface surface breakup in turn leads to a breakup of thesuperconducting d-wave order
parameter into two subband amplitudes along (1,1) & (1,-1) directions and to a low
energy Leggett mode due to phase fluctuations between them. This leads to a large
increase in the temperature range of superconducting fluctuations with an overdamped
Leggett mode. Almost resonant forward scattering of intersubband phonons to a state
with a pair of Leggett modes, causes anomalously strong phonon damping at
wavevectors connecting the ends of the pockets. A close connection in both
temperature and hole density between these anomalously strong superconducting
fluctuations and the Giant Phonon Anomaly.
Reported by Le Tacon et al.
Reference:
[1] Nature Communications 7, 10378, (2016)
40
Tu-S8-2
Mengminwei R139
Tuesday 11:00-11:30
Spectra of intertwined-order states originated from Mott
physics
Wei-Lin Tu1, 2, Peayush Choubey3, P. J. Chen2 , P J Hirschfeld3 , Ting-Kuo Lee2
1. Department of Physics, National Taiwan University, Daan Taipei 10617, Taiwan
2. Institute of Physics, Academia Sinica, Nankang Taipei 11529, Taiwan
3. Department of Physics, University of Florida, Gainesville, Florida 32611, USA
Recently many nearly degenerate intertwined–ordered states were found in the
self-consistent solutions of the renormalized mean-field theory of the lattice t-J
model[1] by taking into account the Gutzwiller factor due to Mott physics. Besides
the charge density waves (CDW) order, these states also include intertwined orders
such as pair density wave (PDW) and/or spin density wave (SDW). The quasiparticle
spectra of one of these states, the anti-phase CDW (AP-CDW) state and its
superconducting associated state, are calculated to compare with the angle-resolved
photoemission spectra(ARPES) of cuprates. These results show many exotic
properties of cuprates, such as Fermi arc at normal state, two gaps and particle-hole
asymmetry at the antinodal direction at superconducting state[2]. By extending the
lattice results to include Wannier functions[3], a continuum local density of states
(LDOS) is calculated. The resulting spatial patterns compare very well with the
scanning tunneling microscopy (STM) experiments[4]. The symmetry of the
intra-unit-cell form factors on the Oxygen sublattice also shows good agreement.
Reference:
[1] SciRep 18675 (2016).
[2] Science 331, 1579 (2011).
[3] Phys. Rev. Lett. 114, 217002 (2015).
[4] arXiv 1507.07865v1
41
Tu-S8-3
Mengminwei R139
Tuesday 11:30-12:00
Strange metal phase and strong correlation
Z. Y. Weng1
1. Center for Advanced Study, Tsinghua University, China
The nature of the strange metal phase in the cuprate superconductor is a mystery.
We argue that it be intimately related to the strong correlation effect based on the t-J
model, where a novel Berry phase precisely keeps the residual quantum memory even
if the spin background gets fully thermalized at high temperature. We show that such
a state is an incoherent bad metal with non-conserving momentum and linear-T
charge resistivity, as dictated by a minimal quantum diffusion constant characterizing
the so-called Planckian dissipation. Various coherent phases as low-temperature
instabilities of this strange metal state will be briefly discussed.
42
Tu-S8-4
Mengminwei R139
Tuesday 12:00-12:15
The t-J-U-V model of high-Tc superconductivity: Full Gutzwiller
wave function solution and quantitative comparison to experiment
J. Spałek1,2 and M. Zegrodnik2
1. Intitute of Physics, Jagiellonian University, Lojasiewicza 11, 30-348 Krakow,
Poland
2. Academic Centre for Materials and Nanotechnology, AGH University of Science
and Technology, Al. Mickiewicza 30, 30-059 Krakow, Poland
The so-called t-J-U-V model (i.e., with inclusion of intra- and inter-atomic
Coulomb interactions is discussed as a general single-band model of high-Tc
superconductivity and solved with the full Gutzwiller wave function (GWF) [1].
Within this approach the renormalized mean-field theory (RMFT) is obtained as the
zeroth-order solution [2]. We show first that RMFT cannot describe correctly either
the experimental data concerning the kinetic energy gain in the superconducting state
or those of the Fermivelocity independence of the doping. Next, the full GWF
solution is analyzed and shown to fit quantitatively these data. On the basis of this
successful approach we argue, that the t-J model must be minimally extended to the
t-J-U-V form and thus the treatment should incorporate both the lower and the upper
Hubbard subbands. Relation of our results to the situation when both the
antiferromagnetic and the charge-density-wave phases are included, is briefly
discussed at the end [3].
The work has been supported by the National Science Center (NCN) under the
grant MAESTRO, No. DEC-2012/04/A/ST3/00342.
Reference:
[1]unpublished.
[2]Phys. Rev. B 88, 115127 (2013); New J. Phys. 16, 073018 (2014).
[3]unpublished.
43
Tu-S9-1
Mengminwei R225
Tuesday 16:00-16:30
Chirality density wave of the “hidden order” phase in URu2Si2
G. Blumberg1, H.-H. Kung1, R. Baumbach2, E. Bauer2, K. Haule1, J. Mydosh3
1.
Rutgers University, Department of Physics and Astronomy, Piscataway, NJ 08854, USA
2. Los Alamos National Laboratory, Los Alamos, NM 87545, USA
3. Kamerlingh Onnes Laboratory, Leiden University, 2300 RA Leiden, Netherlands
Many novel electronic ground states have been found to emerge from the
hybridization between localized d- or f-electron states and conduction electron states
in correlated electron materials. The heavy fermion (HF) compound URu2Si2 exhibits
the coexistence of two such ground states: so-called “hidden order” (HO) below
THO=17.5 K and superconductivity below Tc =1.5 K. Despite 30 years of research the
symmetry of the order parameter associated with HO phase below 17.5 K has
remained ambiguous.
Here we report results of low energy polarization resolved Raman spectroscopy
study aimed to specify the symmetry of collective modes above and below the HO
transition. These excitations involve transitions between interacting heavy uranium 5f
orbitals, responsible for the broken symmetry in the HO phase. From the symmetry
analysis we determine that the HO parameter breaks local vertical and diagonal
reflections at the uranium sites, resulting in crystal field states with distinct chiral
properties, which order to a commensurate chirality density wave ground state [1].
We further explore the competition between the HO phase and large moment
antiferromagnetic (LMAFM) phase and the connection between the HO chirality
density wave and the unconventional superconductivity in URu2Si2, which has
recently been proposed to be of a chiral d-wave type.
Acknowledgments. Research at Rutgers was supported by US Department of
Energy, Office of Basic Energy Sciences, Division of Materials Sciences and
Engineering under Award DE-SC0005463 and by the National Science Foundation
under Awards NSF DMR-1104884 and NSF DMR-1405303.
Reference:
[1] Science, 347, 1339 (2015).
44
Tu-S9-2
Mengminwei R225
Tuesday 16:30-16:45
Unraveling the ground state symmetry of URu2Si2 with NIXS
Martin Sundermann1, Maurits W. Haverkort2, Stefano Agrestini2, Ali Al Zein3, Mark
Golden4,Anne deVisser4, Yinkai Huang4, Peter Thalmeier2, Liu Hao Tjeng2, Andrea
Severing1
1.
2.
3.
4.
Institute of Physics II, University of Cologne, Cologne, Germany
Max-Planck Institute of Chemical Physics of Solids, Dresden, Germany
European Synchrotron Radiation Facility (ESRF), Grenoble, France
Van der Waals-Zeeman Institute, University of Amsterdam, Netherlands
The hidden order (HO) phase transition at 17.5 K in the heavy fermion
superconductor URu2Si2 [1] is a long standing puzzle. The order parameter has still
eluded discovery despite tremendous theoretical and experimental efforts (see [2] and
references therein), but by now it is generally accepted that the multipole moments of
the f electrons are the key to understanding the HO phase.
The multipole moments are intimately linked to the crystal-electric field (CEF)
ground state wave function so that the determination of the ground state symmetry is
crucial in understanding the hidden order in URu2Si2. In an ionic model the Hund‟s
rule ground state of the 5f2 state with J = 4 is split by the tetragonal CEF into five
singlets and two doublets. Which one of these states forms the ground state is not yet
clear. Alone in 2015, two groups found conflicting results; a x-ray absorption (XAS)
and resonant inelastic x-ray scattering experiment (RIXS) by Wray et al. [3] find a
doublet state describing the data best while a polarization-resolved Raman experiment
by Kung et al. [4] clearly favours low lying singlet states.
We will present results of a nonresonant inelastic x-ray scattering experiment
(NIXS) with hard x-rays (also called hard–x ray Raman) at the U O4,5 edge of
URu2Si2: the direction dependence of the scattering function S(q,) (q||c or q||a, q q
momentum transfer) gives the symmetry information in analogy to a polarization
dependent XAS experiment. But moreover, in a hard x-ray NIXS experiment [5]
scattering from higher multipoles contributes to the S(q,) (multipole selection rules)
so that at large q extra excitations appear, yielding extra information. A great
advantage is that NIXS does not involve an intermediate state. It simplifies the
modeling of S(q,) with respect to a resonant experiment and we present simulations
of the NIXS data based on the full multiplet routine Quanty [6]
References:
[1] PRL 55, 2727 (1985)
[2] EPL 89, 57006 (2010) and Phil. Mag. (2013) p 1
[3] PRL 114, 236401 (2015)
[4] Science 347, 1339 (2015)
[5] PRL 109, 046401 (2012)
[6] PRB 85, 165113 (2012)
45
Tu-S9-3
Mengminwei R225
Tuesday 16:45-17:00
Nodal gap structure of the heavy-fermion superconductor URu2Si2
revealed by field-angle-dependent specific-heat measurements
S. Kittaka1, Y. Shimizu1, T. Sakakibara1, Y. Haga2, E. Yamamoto2, Y. Onuki2,3, Y.
Tsutsumi4,5, T. Nomoto6, H. Ikeda7, and K. Machida8
1. Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba, Japan
2. Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki,
Japan
3. Department of Physics, University of the Ryukyus, Nishihara, Okinawa, Japan
4. Department of Basic Science, University of Tokyo, Tokyo, Japan
5. Condensed Matter Theory Laboratory, RIKEN, Wako, Saitama, Japan
6. Department of Physics, Kyoto University, Kyoto, Japan
7. Department of Physics, Ritsumeikan University, Kusatsu, Shiga, Japan
The heavy-fermion superconductor URu2Si2 exhibits novel superconductivity
below Tc = 1.4 K in the mysterious ``hidden-order'' phase. A promising candidate for
its gap symmetry is a chiral d-wave type described by kz(kx+iky), whose gap is
composed of a horizontal line node at equator and point nodes at the north and south
poles. However, previous measurements of the specific heat [1] and the thermal
conductivity [2, 3] did not detect a horizontal line node in the heavy-mass bands,
although it has to be present for the anticipated chiral d-wave state. In order to settle
this controversy, we have performed field-angle-dependent specific-heat
measurements by using a high quality single crystal of URu2Si2 [4]. The
low-temperature specific heat shows the H1/2 behavior in any field direction and a
shoulder-like anomaly in its polar-field-angle dependence. From theoretical analyses
based on microscopic calculations, we have demonstrated that these features are
evidence for the existence of a horizontal line node at kz = 0. Thus, the previous
controversy over the nodal gap structure of URu2Si2 has been settled and the present
results strongly indicate that the gap symmetry of URu2Si2 is of the kz(kx+iky) type.
Reference:
[1] Phys. Rev. Lett. 100, 017004 (2008).
[2] Phys. Rev. Lett. 99, 116402 (2007).
[3] New J. Phys. 11, 055061 (2009).
[4] arXiv:1511.06060 (to appear in J. Phys. Soc. Jpn.).
46
Tu-S9-4
Mengminwei R225
Tuesday 17:00-17:15
Ferromagnetic superconductivity and Fermi surface instabilities in
uranium compounds
Dai Aoki1,2, Adrien Gourgout1, Gael Bastien1, Alexandre Pourret1, Georg Knebel1,
Beilun Wu1, Jean-Pascal Brison1, Jacques Flouquet1
1. INAC/SPSMS, CEA-Grenole, 38054 Grenoble, France
2. IMR, Tohoku University, Oarai, Ibaraki 311-1313, Japan
The coexistence of ferromagnetism and superconductivity(SC) in three uranium
compounds UGe2, URhGe and UCoGe attracts much interest[1], because the
spin-triplet state with equal spin paring and the unusual field-induced phenomena are
realized. Their ordered moments are 1.5, 0.4 and 0.05 muB, respectively, and the 5f
electrons with itinerant nature are believed to be responsible both for magnetism and
for superconductivity. We focus on pressure (P) and magnetic field (H) response on
the magnetic fluctuations and Fermi Surfaces and their feedback on
superconductivity.
Special attention is given on the field-reinforced superconductivity and the
ferromagnetic fluctuations in URhGe and UCoGe. When the field is applied along the
hard-magnetization axis (b-axis), the upper critical field Hc2 shows the unusual
S-shaped or field reentrant behavior in (H,T) phase diagram[2,3], extremely
exceeding the Pauli limit. The strong Ising-type magnetic fluctuations are
demonstrated by the anisotropic field-dependent effective mass. Quite recent Hall
effect[4] and thermopower macroscopic measurements[5] in URhGe and UCoGe
suggest Fermi surface change at high fields. Direct evidences are confirmed by dHvA,
SdH effect and the quantum oscillations in thermopower[5].
In URhGe, pressure moves the system deeper in the ferromagnetic domain, H
reentrant SC collapses more rapidly than low field ones. On the other hand, in UCoGe,
the great interest is that a moderate pressure Pc of 1GPa is sufficient to enter in the
paramagnetic ground state. Furthermore as the initial sublattice magnetization is low,
collapse of ferromagnetism may be dominated by the ferromagnetic fluctuations; new
careful pressure studies of Hc2(T) with anisotropic field response will be reported[6]
and discussed on the basis on the interplay between magnetic fluctuations and Fermi
surface topology. Finally, thermal conductivity experiments on UCoGe at ambient
pressure emphasize the multiband character of its superconductivity[7].
Reference:
[1] J. Phys. Soc. Jpn. 83, 061011 (2014).
[2] Science 309, 1343 (2005).
[3] J. Phys. Soc.Jpn. 78, 113709 (2009).
[4] J. Phys. Soc. Jpn. 83, 094719 (2014).
[5] to be published.
[6] to be published.
[7] Phys. Rev. B 90, 180501 (2014).
47
Tu-S9-5
Mengminwei R225
Tuesday 17:15-17:30
Local magnetic properties in the ferromagnetic superconductor
UCoGe probed by XMCD
F. Wilhelm1, M. Taupin2,3, J.-P. Sanchez2, J.-P. Brison2, D. Aoki2,4, G. Lapertot2, A.
Rogalev1
1. European Synchrotron Radiation Facility (ESRF), Grenoble, France
2. Univ. Grenoble-Alpes, INAC-SPSMS, CEA Grenoble, France
3. Low Temperature Laboratory, Aalto University, Aalto, Finland
4. Institute for Materials Research, Tohoku University, Oarai,, Japan
Magnetic properties of the ferromagnetic superconductor UCoGe have been
investigated using an element selective technique such as x-ray magnetic circular
dichroism (XMCD) 1. XMCD spectra have been measured at the M4,5-edges of
Uranium and at the K-edges of Co and Ge. The analysis of the branching ratio in
x-ray absorption spectra at the U M4,5 -edges reveals that the U 5f electrons count is
close to 3 and independent of applied magnetic field. Using XMCD sum rules it is
shown that the U 5f states acquire a magnetic moment of ∼0.4µB (mL∼0.70µB and
mS∼-0.30µB) at 2.1K and under magnetic field of 17T applied along the c axis of the
crystal. The ratio mL/mS being close to −2.3 suggests a significant delocalization of
the 5f electron states. The XMCD at the K-edges of Co and Ge reveal the presence of
small Co 4p and Ge 4p orbital moments both parallel to applied field and therefore to
the Uranium total moment and to the macroscopic sample magnetization. Moreover,
comparison of the XMCD spectra at the Co K-edge in UCoGe and UCoAl single
crystals allowed us to estimate the Co 3d moment in the former to be at most of 0.1µB
at 17 T. Thus, our results rule out the model of an unusual polarizability of the U and
Co moments as well as their antiparallel coupling. We conclude that the
ferromagnetism, which is considered to mediate superconductivity in UCoGe, is
governed by the U 5f states.
Reference:
[1]PRB 92, 035124 (2015).
48
Tu-S10-1
Mengminwei R139
Tuesday 16:00-16:30
Peculiar Properties of the Cr3As3-Chain Based Superconductors
G. H. Cao1,2, J. K. Bao1,2 , Y. Liu1,2, H. K. Zuo3, Z. T. Tang1,2 , Z. W. Zhu3
2.
3.
1. Department of Physics, Zhejiang University, Hangzhou 310027, China;
Collabortative Innovation Center of Advanced Microstructures, Nanjing 210093, China;
Wuhan National High Magnetic Field Center, School of Physics, Huazhong University of
Science and Technology, Wuhan 430074, China
The discovery of superconductivity in Cr-based arsenides A2Cr3As3 (A=K,Rb,Cs)
[1] has attracted considerable research interest. In this talk I will briefly overview the
recent research progresses ranging from the crystal-structure and electronic-structure
characteristics to the normal-state and superconducting properties. Overall, the results
support unconventional superconductivity with a dominant spin-triplet pairing in this
new superconducting family. Nevertheless, many open questions need to be addressed
in the future.
References:
[1] J. K. Bao et al., Phys. Rev. X 5, 011013 (2015); Z. T. Tang et al., Phys. Rev. B 91,
020506(R) (2015); Z. T. Tang et al., Science China Materials 58, 16 (2015).
49
Tu-S10-2
Mengminwei R139
Tuesday 16:30-16:45
Nodal superconducting-gap structure in the quasi-one-dimensional
Cs2Cr3As3 investigated using μSR measurements
D. T. Adroja1, 2, , A. Bhattacharyya1, 2, M. Smidman3, A. D. Hillier1, Yu. Feng4, B.
Pan4, J. Zhao4, M. R. Lees5, and A. M. Strydom2
1.
ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot Oxon, OX11 0QX, United
Kingdom
2. Highly Correlated Matter Research Group, Physics Department, University of Johannesburg,
PO Box 524, Auckland Park 2006, South Africa
3. Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou
310058, China
4. State Key Laboratory of Surface Physics and Department of Physics, Fudan University,
Shanghai 200433, China
5. Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
The superconducting gap structure of the newly discovered superconductor
Cs2Cr3As3 with a quasi-one-dimensional crystal structure (Tc ∼ 2.2 K) has been
investigated using magnetization and muon-spin relaxation or rotation (μSR), using
both zero-field (ZF) and transverse-field (TF), measurements. Our ZF μSR
measurements reveal the presence of spin fluctuations below 4 K and the ZF
relaxation rate (λ) shows an enhancement below (Tc ∼ 2.2 K), which may indicate
that the superconducting state is not conventional. This observation suggests that the
electrons are paired via unconventional channels such as spin fluctuations, as
proposed on the basis of theoretical models of the A2Cr3As3 compounds. Our analysis
of the TF-μSR data shows that the temperature dependence of the superfluid density
is fitted better with a nodal gap structure than an isotropic s-wave model (i.e. nodeless
gap) for the superconducting gap. The observation of a nodal gap in Cs 2Cr3As3 is
consistent with that observed in isostructural K2Cr3As3. Furthermore, from our
TF-μSR study we have estimated the magnetic penetration depth λL, superconducting
carrier density ns, and carriers‟ effective-mass enhancement m∗.
*E-mail: [email protected]
50
Tu-S10-3
Mengminwei R139
Tuesday 16:45-17:00
Electronic structure and superconductivity in the layered iron
germanide YFe2Ge2
J. C. Baglo1, P. Reiss1, J. Chen1, K. Semeniuk1, P. Brown1, G. I. Lampronti2, Z.
Feng3, F. M. Grosche1
1. Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
2. Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom
3. London Centre of Nanotechnology, University College London, London, United Kingdom
The d-electron system YFe2Ge2 is notable among transition metal compounds for
its unusually large Sommerfeld coefficient C/T ≈ 100 mJ/mol K2, along with a
non-Fermi-liquid power law temperature dependence of resistivity, indicative of a
strongly correlated metal. High quality samples of YFe2Ge2 superconduct below Tc ≈
1.8 K [1]. Recent progress in sample growth [2] has produced samples with residual
resistivity ratios exceeding 200, which display clear superconducting heat capacity
anomalies and full diamagnetic screening, confirming that superconductivity is
intrinsic to YFe2Ge2.
DFT band structure calculations [3] reveal striking similarities between the Fermi
surface of YFe2Ge2 and that of the high pressure collapsed tetragonal phase of
KFe2As2, in which superconductivity with a Tc as high as 10 K has recently been
reported [4]. We present new specific heat and upper critical field measurements,
along with a study of the disorder dependence of Tc, suggesting an unconventional
mechanism for superconductivity in YFe2Ge2, and discuss implications for the related
collapsed tetragonal phase of the alkaline metal iron arsenides.
References:
[1] Y. Zou et al., Physica Status Solidi (RRL) 8, 928 (2014).
[2] J. Chen et al., arXiv:1507.01436 (2015).
[3] A. Subedi, Phys. Rev. B 89, 024504 (2014); D. J. Singh, Phys. Rev. B 89, 024505
(2014).
[4] J-J. Ying et al., arXiv:1501.00330 (2015); Y. Nakajima et al., Phys. Rev. B 91,
060508(R) (2015).
51
Tu-S10-4
Mengminwei R139
Tuesday 17:00-17:15
Vibrational dynamics of cage compounds
A. Leithe-Jasper1, M. M. Koza2, Yu. Grin1
1.
Max-Planck Institute for Chemical Physics of Solids, Dresden , Germany
2. ILL, Grenoble, France
In many cage-compounds experiments established the presence of apparently
localized vibrational modes at energies as low as a few meV only, i.e. within the
range of acoustic phonons. Compounds have to be studied whose low-energy
dynamics is known to have a primary impact on the lattice thermal conductivity and
can be tuned in a wide range of energies by the inclusion of distinct electropositive
elements. These and related materials are characterized by having voids in their host
structures, which can accept electropositive atoms as guests. These guests are loosely
bound in their oversized cages and dissipate the vibrational energy but do not obstruct
the electrical current.
We studied the vibrational dynamics of a single crystal of LaFe4Sb12 by three-axis
inelastic neutron spectroscopy [1]. The dispersion of phonons with wave vectors q
along [xx0] and [xxx] directions in the energy range of eigenmodes with high
amplitudes of lanthanum vibrations, i.e., at ħω less than or similar to 12 meV is
identified. Symmetry-avoided anticrossing dispersion of phonons is established in
both monitored directions and distinct eigenstates at high-symmetry points and at the
Brillouin-zone center are discriminated. The experimentally derived phonon
dispersion and intensities are compared with and backed up by ab initio lattice
dynamics calculations (LDC).
As a second example we report on the inelastic response of AV2Al20 (with A = Sc,
La and Ce) probed by high-resolution inelastic neutron scattering experiments [2].
Intense signals associated with the dynamics of Sc, La and Ce are identified in the
low-energy range at 6-14 meV in ScV2Al20 and at 8-16 meV in LaV2Al20 and
CeV2Al20. Their response to temperature changes between 2 and 300 K reveals a very
weak softening of the modes upon heating in LaV2Al20 and CeV2Al20 and a
distinguished blue shift by about 2 meV in ScV2Al20. By means of density functional
theory (DFT) and LDC we show that the unusual anharmonicity of the Sc-dominated
modes is due to the local potential of Sc featured by a strong quartic term. The
vibrational dynamics of ScV2Al20 as well as of LaV2Al20 and CeV2Al20 is reproduced
by a set of eigenmodes. The effect of the strong phonon renormalization in ScV2Al20
on thermodynamic observables is computed on grounds of the LDC derived inelastic
response.
Reference:
[1] M. M. Koza, M. Boehm, E. Sischka, W. Schnelle, H. Mutka A. Leithe-Jasper,
Phys. Rev. B 91, 014305 (2015)
[2] M. M. Koza et al., Phys. Chem. Chem. Phys. 16, 27119 (2014)
52
Tu-S10-5
Mengminwei R139
Tuesday 17:15-17:30
Superconductivity in Weyl Semimetal Candidate MoTe2
Yanpeng Qi1, Pavel G. Naumov1, Mazhar N. Ali2, Catherine R. Rajamathi1, Walter
Schnelle1, Oleg Barkalov1, Michael Hanfland3, Shu-Chun Wu1, Chandra Shekhar1,
Yan Sun1, Vicky Süß1, Marcus Schmidt1, Ulrich Schwarz1, Eckhard Pippel4, Peter
Werner4, Reinald Hillebrand4, Tobias Förster5, Erik Kampert5, Stuart Parkin4, R. J.
Cava2, Claudia Felser1, Binghai Yan1,6*, Sergey A. Medvedev1
1.
Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
3. European Synchrotron Radiation Facility, BP 220, Grenoble 38043, France
4. Max Planck Institute of Microstructure Physics, 06120 Halle, Germany
5. Dresden High Magnetic Field Laboratory (HLD-EMFL), Helmholtz-Zentrum
Dresden-Rossendorf, 01328 Dresden, Germany
6. Max Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany
2.
Transition metal dichalcogenides have attracted research interest over the last few
decades dueto their interesting structural chemistry, unusual electronic properties, rich
intercalation chemistry and wide spectrum of potential applications. Despite the fact
that the majority ofrelated research focuses on semiconducting transition-metal
dichalcogenides e.g., MoS2,recently discovered unexpected properties of WTe2 are
provoking strong interest in semimetallic transition metal dichalcogenides featuring
large magnetoresistance, pressuredriven superconductivity, and Weyl semimetal state.
We investigate the sister compound of WTe2, MoTe2, predicted to be a Weyl
semimetal and a quantum spin Hall insulator in bulk and monolayer form,
respectively. We find that bulk MoTe2 exhibits superconductivity with a transition
temperature of 0.10 K and application of external pressure dramatically enhances the
transition temperature up to maximum value of 8.2 K at 11.7 GPa. Observed
dome-shaped superconductivity phase diagram provides insights into the interplay
between superconductivity and topological physics.
References
[1] Qi et al. Nature Commun. Accepted (2016)
53
We-S11-1
Mengminwei R225
YbRh2Si2 – A New Heavy-Fermion Superconductor
F. Steglich
Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
Center for Correlated Matter, Zhejiang University, Hangzhou, Zhejiang 310058, China
Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Unconventional superconductivity often occurs in the vicinity of quantum critical
points (QCPs) in antiferromagnetic (AF) heavy-fermion metals. However, no
superconductivity has so far been observed near some of the canonical heavy-fermion
QCPs, such as the one induced by a magnetic field in YbRh2Si2, raising the question
about the generality of this paradigm. Here, we will explore the possibility of reaching
the quantum critical regime by sufficiently weakening the AF order through its
coupling to nuclear spins at very low temperatures, instead of applying a
pair-breaking magnetic field. To this end, we discuss results of magnetic and
calorimetric measurements on YbRh2Si2 down to T = 1mK. They reveal the onset of a
hybrid nuclear-electronic type of AF order dominated by the Yb-derived nuclear spins
at TA slightly above 2 mK and the subsequent development of superconductivity at Tc
= 2 mK. The initial slope of the upper critical field curve, Bc2(T), at Tc is found to be
as large as - Bc2‟ ≌ 25 T/K. This indicates that the effective charge-carrier mass
must be of the order of several 100 mel, implying that the superconducting state is
associated with the Yb-derived 4f electrons. The apparent heavy-fermion
superconductivity in YbRh2Si2 may be called “high Tc”, in the sense that it is limited
by an exceedingly high ordering temperature of nuclear spins (TA ≳ 2 mK as
compared to common values in the nK range). Also, we briefly address the theoretical
possibility of superheavy-fermion superconductivity based upon an underlying
nuclear Kondo effect. In conclusion, we ascribe the formation of Cooper pairs in
YbRh2Si2 to the critical fluctuations associated with the unconventional QCP of this
antiferromagnet, which are revealed when the primary electronic order is diminished
by the competing nuclear order. Our results demonstrate a new means to reach an AF
QCP and provide further evidence that superconductivity in the vicinity of such an
instability is a general phenomenon.
Reference:
E. Schuberth, M. Tippmann, L. Steinke, S. Lausberg, A. Steppke, M. Brando, C.
Krellner, C. Geibel, R. Yu, Q. Si and F. Steglich, Science 351, 485 (2016).
54
We-S11-2
Mengminwei R225
Orbital Exchange and Fractional Quantum Number Excitations in
Yb2Pt2Pb
Meigan Aronson
Texas AM University
Strongly correlated electron systems display a variety of orders, and it is increasing
believed that these phases may be organized at T=0 in a universal phase diagram with
two different sources of quantum criticality. The interplay between electronic
delocalization driven by coupling between the conduction electrons and localized
moments can lead to a transition or crossover between two phases with different sized
Fermi surfaces, although a purely magnetic transition may be found in systems with
strong quantum fluctuations, due to low dimensionality or geometrical frustration.
Yb2Pt2Pb is a promising example of a magnetically frustrated system where Yb
moments with strong Ising anisotropy lie on orthogonal spin ladders. Although these
moments might be considered classical, being in a nearly pure state with jZ=±7/2,
neutron scattering measurements find an incoherent continuum of magnetic
excitations, direct evidence that electrons carry a fractional spin quantum number.
These excitations disperse only along the chain direction, and they resemble the
spinon dispersion that is found in S=1/2 Heisenberg spin chains with only weak
magnetic anisotropy. This unexpected quantum behavior emerges at low energies
from the competition between strong onsite and spin-orbit interactions, the crystal
fields, and the intersite hopping, all acting on much higher energy scales. Magnetic
fields collapse the spinon gap, and lead to the formation of new gapless states
constructed from right and left moving spinons. The formation of this new Fermi
surface is documented in neutron scattering measurements.
This research is a collaboration with W. Gannon, L. S. Wu, M. S. Kim, I. Zaliznyak,
A. M. Tsvelik, Y. Qiu, J. Copley, G. Ehlers, A. Podlesnyak, and J. S. Caux. It was
supported by NSF- DMR131008 (WG, LSW, MSK, MCA) and by the Department of
Energy,Office of Basic Energy Sciences (IZ, AMT) under contract DE-SC00112704.
55
We-S11-3
Mengminwei R225
Field Induced Quantum Criticality without Magnetism in α-YbAlB4
Yosuke Matsumoto1, A. Magata1, Y. Shimura1, T. Tomita1, R. Küchler2, M. Brando2,
S. Nakatsuji1
1.
2.
Institute for Solid State Physics, University of Tokyo,Chiba, Japan.
Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
So far, quantum criticality (QC) in heavy fermion systems has been studied mainly
for Kondo lattice systems with integer valence, where a quantum critical point (QCP)
is normally associated with magnetism. In contrast, the first Yb-based heavy fermion
superconductor α-YbAlB4 provides a unique example of QC in the mixed valent
compounds, which goes beyond the conventional idea based on a magnetic QCP [1-5].
Indeed, the QC cannot be explained by the standard spin fluctuation mechanism.
Instead, this emerges without tuning any control parameter, indicating formation of a
strange metal phase [4]. A recent observation of a non-Fermi liquid phase, stable over
a finite pressure range up to ~ 0.4 GPa, further supports the idea [5].
On the other hand, an isostructural polymorph α-YbAlB4 exhibits Fermi liquid
ground state at zero-magnetic field [6], which is in sharp contrast to the zero-field QC
in α-YbAlB4. Nevertheless, the emergence of the heavy fermion state with a
characteristic temperature scale of ~ 8 K suggests that this compound also locates
close to a QCP. Indeed, recent studies revealed a sharp valence crossover induced by
a chemical substitution [7] and a field induced non-Fermi liquid (NFL) at a small
magnetic field of BL ~ 2.1 T and BU ~ 3.6 T applied along the c-axis [8].
Here we discuss the origin of the field induced NFL using the results of the thermal
expansion / magnetostriction measurements on α-YbAlB4. Our results indicate highly
anisotropic heavy fermion formation with negative thermal expansion only in the
ab-plane at zero-field. Furthermore, the magnetostriction data in the ab-plane and
along the c-axis clearly indicate two different field scales corresponding BL and BU,
respectively. In addition, we found the sign change of the linear thermal expansion
coefficient along the c-axis at BU, which strongly indicates the existence of a QCP. On
the other hand, quantum oscillation measurements further suggests that the QC at BL
is driven by a Lifshitz transition. All these observations indicate a realization of
unconventional QCs without magnetic order in this compound. We will further
discuss the possible roles played by anisotropic hybridization, valence fluctuation,
combining the results obtained from various probes.
Reference:
[1] S. Nakatsuji et al., Nature Phys. 4, 603 (2008).
[2] K. Kuga et al., Phys. Rev. Lett. 101, 137004 (2008).
[3] M. Okawa et al., Phys. Rev. Lett. 104, 247201 (2010).
[4] Y. Matsumoto et al., Science 331, 316 (2011).
[5] T. Tomita et al., Science 349, 506 (2015).
[6] Y. Matsumoto et al., Phys. Rev. B 84, 125126 (2011).
[7] K. Kuga, Y. Matsumoto et al., preprint (2016).
[8] E. C. T. O‟Farrell, M. Grbic, Y. Matsumoto et al., preprint (2016).
56
We-S11-4
Mengminwei R225
The superconducting order parameter of the heavy fermion
superconductor CeCu2Si2
M. Smidman1, G. M. Pang1, Z. F. Weng1, Y. Chen1, W. B. Jiang1, Y. J. Zhang1,
J. L. Zhang1, L. Jiao1, H. S. Jeevan2, F. Steglich1,2, and H. Q. Yuan1,3*
1
Center for Correlated Matter and Department of Physics, Zhejiang University,
Hangzhou 310058, China
2
Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, D-01187
Dresden, Germany
3
Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093,
China
CeCu2Si2 was the first heavy fermion superconductor to be discovered [1], but
despite being studied intensively for over 35 years, the nature of the superconducting
order parameter is not well understood. Previously CeCu2Si2 was generally believed
to be a d-wave superconductor with line nodes in the gap [2,3], but fully gapped
superconductivity was recently reported from low temperature specific heat
measurements [4]. We report measurements of the London penetration depth of single
crystals of CeCu2Si2 using a tunnel diode based method, which are also consistent
with fully gapped superconductivity. The various possible scenarios for the gap
symmetry of CeCu2Si2 will be discussed, with reference to both our experimental data
and the literature.
[1] F. Steglich et al., Phys. Rev. Lett. 43, 1892-1896 (1979).
[2] Y. Kitaoka et al., J. Phys. Soc. Jpn. 55, 723-726 (1986).
[3] O. Stockert et al., Nature Physics 7, 119-124 (2011).
[4] S. Kittaka et al., Phys. Rev. Lett 112, 067002 (2014).
57
We-S11-5
Mengminwei R225
Pr2Pt3Ge5 a novel magnetic superconductor
D. G. Mazzone1, R. Sibille2, J. L. Gavilano1, M. Bartkowiak2, M. Månsson1, M.
Frontzek1, O.Zaharko1, J. Schefer1, M. Kenzelmann2
1.
2.
1Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen PSI,
Switzerland
2Laboratory for Scientific Developments and Novel Materials, Paul Scherrer Institut, 5232
Villigen PSI, Switzerland
Pr2Pt3Ge5 is a superconductor with Tc = 7.8 K which displays two antiferromagnetic
transitions at TN1 = 3.4 and TN2 = 4.1 K, deep in the superconducting phase. The low
temperature magnetic phase is commensurate with ordered moments of μ = 2.3 μB and a
propagation vector of q = (0,1,0). The high temperature phase, between TN1 and TN2 is
incommensurate with ordered moments of μ = 2 μB and a propagation vector of q = (0,
0.85,0). In both phases the moments are in the ab plane. Although Hc2 is isotropic, the
magnetic phases are not. They are sensitive to the orientation of the external field. For
instance, for H||(001) direction, both magnetic phases survive, up to near 7 T (CM
phase) and 9 T (ICM phase) well outside of the superconducting phase (Hc2= 1.6 T).
Whereas for H||(010) the magnetic phases are always inside the superconducting phase.
These results show that the superconducting and magnetic phases are completely
decoupled.
Reference:
[1] N.H Sung et al., PRB 86, 224507 (2012)
[2] D. Mazzone et al., arXiv:1508.02649 (2015)
58
We-S12-1
Mengminwei R139
Large anomalous Hall effect in chiral antiferromagnets at room
temperature
S. Nakatsuji1, N. Kiyohara1, T. Higo1, and T. Tomita1
1.
Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa 277-8581, Japan
Anomalous Hall effect (AHE) is one of the most fundamental transport properties
of solid. Since its discovery, the effect is known to be proportional to magnetization
and thus the zero field AHE has been observed only in ferromagnets. Hypothetically,
however, since intrinsic AHE arises owing to fictitious fields due to Berry curvature,
it may appear in spin liquids and antiferromagnets without spin-magnetization in
certain conditions. Indeed, a spontaneous Hall effect has been observed in recent
experiments in the spin liquid Pr2Ir2O7 [1]. In this talk, we will present our
experimental observation of a large Hall effect in non-collinear antiferromagnets. In
particular, we found that the antiferromagnets Mn3Sn [2] and Mn3Ge [3], which have
a non-collinear chiral spin order known as an inverse triangular spin structure, exhibit
a large anomalous Hall effect at room temperature. Moreover, the sign of the giant
AHE can be softly flipped by the rotation of magnetic field, indicating that the
direction of a fictitious field equivalent to a few 100 T is tunable by a small external
magnetic field less than 0.1 T and thus the AHE could be useful for applications.
Possible role of Weyl points in the k-space will be also discussed.
References
[1] Y. Machida S. Nakatsuji, S. Onoda, T. Tayama, and T. Sakakibara, Nature 463,
210 (2010).
[2] S. Nakatsuji, N. Kiyohara and T. Higo, Nature 527, 212 (2015).
[3] N. Kiyohara, T. Tomita, and S. Nakatsuji, arXiv:1511.03128
59
We-S12-2
Mengminwei R139
Magnetoelastic Correlations, Frustration, and Bose-Einstein
Condensation in Quantum Magnets
Marcelo Jaime
Los Alamos National Laboratory, Los Alamos, NM, USA
National High Magnetic Field Laboratory
Quantum magnets are natural realizations of gases of interacting bosons whose
relevant parameters such as dimensionality, lattice geometry, amount of disorder,
nature of the interactions, and particle concentration can vary widely between
different compounds. The particle concentration can be easily tuned by applying an
external magnetic field which plays the role of a chemical potential. This rich
spectrum of realizations offers a unique possibility for studying the different physical
behaviors that emerge in interacting Bose gases from the interplay between their
relevant parameters. The plethora of other bosonic phases that can emerge in quantum
magnets, of which the Bose-Einstein condensate is the most basic ground state, is
intriguing and not always easy to predict [1]. Here we review recent results with some
attention paid to the strength of magnetoelastic correlations in quantum magnets as a
smoking gun for frustration and broken symmetries crucial to determine the nature of
the ground state.
Reference:
[1] V. Zapf, M. Jaime, and C.D. Batista, Rev. Mod. Phys. 86, 563 (2014).
60
We-S12-3
Mengminwei R139
NMR Evidence for a Gapped Spin Liquid Ground State in the S =1/2
Kagome Heisenberg Antiferromagnet ZnCu3(OH)6Cl2
Mingxuan Fu1, 3, Takashi Imai1, 2, Tianheng Han4, Young. S. Lee5, 6
Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S4M1,
Canada.
2. Canadian Institute for Advanced Research, Toronto, ON M5G1Z8, Canada.
3. Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins
University, Baltimore, MD 21218
4. James Franck Institute and Department of Physics, University of Chicago, Chicago, IL
60637, USA.
5. Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139.
6. Department of Applied Physics and Department of Photon Science, Stanford University and
SLAC National Accelerator Laboratory, Stanford, CA 94305.
1.
The S = 1/2 kagome Heisenberg antiferromagnet is a leading contender for an
experimental realization of a quantum spin liquid (QSL) ground state. The recent
discovery of a continuum of spinon excitations using inelastic neutron scattering [1]
has stimulated intense research into its physical properties. However, the nature of the
paramagnetic ground state in this material remains highly debated, primarily owing to
the difficulty in revealing the intrinsic magnetic behavior of the kagome lattice from
defect contributions. Through single-crystal 17O NMR measurements, we demonstrate
that the intrinsic spin susceptibility 𝜒𝑘𝑎𝑔𝑜𝑚𝑒 tends asymptotically to zero below
T~0.03J, where J ~ 200K is the Cu-Cu superexchange interaction. Combined with the
magnetic field dependence of the 𝜒𝑘𝑎𝑔𝑜𝑚𝑒 observed at low temperatures, our results
provide direct evidence for a QSL state with a finite gap Δ = 0.03~ 0.07J realized in
ZnCu3(OH)6Cl2 [2].
Reference:
[1] T. H. Han, J. S. Helton, S. Chu, D. G. Nocera, J. A. Rodriguez-Rivera, C.
Broholm and Y. S. Lee, Nature 492, 406 (2012).
[2] M. Fu, T. Imai, T. H. Han and Y. S. Lee, Science 350, 655 (2015).
61
We-S12-4
Mengminwei R139
Ca10Cr7O28 - Physical realization of a quantum spin liquid
based on a novel frustration mechanism
Christian Balz1,2, Bella Lake1,2, Johannes Reuther1,3, Hubertus Luetkens4, Rico
Schönemann5, Thomas Herrmannsdörfer5, Yogesh Singh6, A.T.M. Nazmul Islam1,
Elisa M. Wheeler7, Jose A. Rodriguez-Rivera8, Giovanna G. Simeoni9, Chris Baines4,
and Hanjo Ryll
1.
Helmholtz-Zentrum Berlin für Materialien und Energie, 14109 Berlin, Germany,
Institut für Festkörperphysik, Technische Universität Berlin, 10623 Berlin, Germany,
3. Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität
Berlin, 14195 Berlin, Germany,
4. Laboratory for Muon-Spin Spectroscopy, Paul Scherrer Institut, 5232 Villigen, Switzerland,
Hochfeld
5. Magnetlabor Dresden (HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden,
Germany,
6. Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector
81, Mohali 140306, India,
7. Institut Laue-Langevin, 38042 Grenoble, France,
8. NIST Center for Neutron Research, National Institute of Standards and Technology, 20899
Gaithersburg, USA,
9. Heinz Maier-Leibnitz Zentrum, Technische Universität München, 85748 Garching, Germany
2.
We describe the much sought after quantum spin liquid state in the new frustrated
magnet, Ca10Cr7O28, whose coupling mechanism does not correspond to the currently
proposed candidates for spin liquid physics (e.g. triangular, kagome and pyrochlore
lattice) [1]. Ca10Cr7O28 features independent bilayers of corner sharing triangles of
S-½ Cr5+ ions building a quasi-kagome network. Ferromagnetic interactions link
ferromagnetic triangles from one part of the bilayer to antiferromagnetic ones in the
second part and the frustration arises from the opposite sign of the coupling within the
two triangles where neither triangle can realize its intrinsic spin arrangement. Heat
capacity, AC susceptibility and muon spectroscopy reveal a ground state that holds
neither long-range magnetic order nor any static magnetism but features coherent spin
dynamics which persist down to the lowest temperatures. Inelastic neutron scattering
patterns taken in the ground state show broad and diffuse excitations which closely
resemble the expected fractionalized excitations of a 2D quantum spin liquid [2,3].
The frustration can be overcome by moderate external magnetic field resulting in
sharp magnon excitations and by fitting their dispersions to linear spin wave theory
the spin Hamiltonian was extracted. From this Hamiltonian the ground state
correlations of Ca10Cr7O28 are reproduced using Functional Renormalization Group
calculations. This is a rare example where it is shown both experimentally and
theoretically that a Hamiltonian involving substantial ferromagnetic interactions and
no anisotropy is prone to a quantum spin liquid ground state [4].
References:
[1] L. Balents, Nature 464, 199 (2010)
[2] T.-H. Han et al., Nature 492, 406 (2012)
[3] M. Punk et al., Nature Physics 10, 289 (2014)
[4] C. Balz et al., Nature Physics, submitted (2016)
62
We-S12-5
Mengminwei R139
Thermal conductivity of exotic elementary excitations in quantum
spin ice
Y. Tokiwa1,2, T. Yamashita1, D. Terazawa1, M. Udagawa3, Y. Yasui4, S. Kittaka5, T.
Sakakibara5, K. Kimura5, M. Halim5, S. Nakatsuji5, T. Terashima2, T. Shibauchi6, Y.
Matsuda1
Research Center for Low Temperature and Materials Science, Kyoto University, Kyoto,
Japan
3. Department of Physics, Gakushuin University, Mejiro, Toshima-ku, Tokyo, Japan
4. Department of Physics, School of Science and Technology, Meiji University, Kawasaki,
Japan
5. Institute for Solid State Physics, University of Tokyo, Kashiwa, Japan
6. Department of Advanced Materials Science, University of Tokyo, Chiba, Japan
2.
Novel elementary excitations, quantum magnetic monopoles and artificial photon
may emerge in quantum spin ice systems [1,2]. We report highly unusual thermal
conductivity of rare-earth pyrochlores, Yb2Ti2O7 and Pr2Zr2O7, which contain spin-ice
correlations with significant quantum fluctuations. Observed anomalous temperature
and field dependences of κ in these compounds indicate coherent propagations of
exotic magnetic excitations.
In the spin liquid state of Yb2Ti2O7 above the ferromagnetic transition temperature
of 0.2K, our analysis evidences strongly suppressed monopole excitation gap,
indicating significant modification of monopole excitation spectrum due to quantum
fluctuations [3]. Moreover, the emergent quantum monopoles are highly mobile with
extremely long mean free path, in contrast to the diffusive classical monopoles. The
quantum monopole is, thus, a novel heavy particle, that propagates almost ballistically
in a three-dimensional spin liquid.
In Pr2Zr2O7, the absence of magnetic ordering even at very low temperature
suggests formation of the quantum spin liquid [4]. Interestingly, our data of κ/T shows
anomalous steep increase with decreasing temperature below 0.2K. Since the
monopole density is negligibly small at such low temperature, the steep increase
possibly indicates emergence of the novel elementary excitation, artificial photon.
Unusual magnetic-field dependence of κ/T observed at low temperatures further
supports this possibility.
Reference:
[1] M. Hermele, et al., Phys. Rev. B 69, 064404 (2004).
[2] O. Benton, et al., Phys. Rev. B 86, 075154 (2012).
[3] Y. Tokiwa, et al., arXiv:1504.02199
[4] K. Kimura, et al., Nature Commun. 4, 1934 (2013).
63
Th-S13-1
Mengminwei R225
Thursday 8:30-9:00
Detection of Kondo Transmission Phase with a Quantum Dot
Interferometer
S. Tarucha1,2
1Applied Physics Department, The University of Tokyo, Tokyo, Japan
2 Center for Emergent Matter Science (CEMS), RIKEN, Saitama, Japan
Recent advances in nanotechnology have allowed us to study the Kondo interaction
of a single spin localized in semiconductor quantum dots in contact with an electron
reservoir in a controlled manner, resulting in discovery of various kinds of novel
Kondo features. These studies have also enabled access to the phase shift across a
Kondo impurity, a central ingredient of Nozières' celebrated Fermi-liquid theory for
the Kondo effect: A sufficiently low-energy electron scatters coherently off the
Kondo singlet, acquiring a π/2-phase shift. The Kondo phase measurements have been
pursued in pioneering experiments with an Aharonov-Bohm ring incorporating a
quantum dot. However, the obtained phase shift has been unexpected and inconsistent
with theory. We have recently developed a new type of two-path interferometer
including a quantum dot that enables to measure the electron transmission phase
through the dot [1,2], and applied it to detect the phase shift through a Kondo
correlated quantum dot. We have observed a clear π/2-phase shift in the Kondo valley
of the dot. We have also found that the change of the Kondo phase observed below
and above the Kondo temperature is consistent with renormalization group
calculations [3].
Reference:
[1] Nat. Nano.7, 247 (2012).
[2] APL 107, 063101 (2015).
[3] PRL 113, 126601 (2014).
64
Th-S13-2
Mengminwei R225
Thursday 9:00-9:30
From Kondo lattices to Kondo superlattices; exploring the interface
between heavy and normal electrons
Y. Matsuda
Condensed matter systems that are both low-dimensional and strongly interacting
often exhibit unusual electronic properties, with the high-Tc superconductivity in
cuprates and iron pnictides as the most prominent example. A metallic state with the
strongest electron correlation is realized in heavy fermion compounds, whose
electronic structure is essentially 3D. Recently, by fabricating epitaxial superlattices
built of alternating layers of Ce-based heavy-fermion and La- or Yb-based
conventional nonmagnetic metals, we have succeeded in confining heavy fermions to
two dimensions, resulting in slices of 2D Kondo lattice. Here we will discuss the
following topics.
1)STM study of epitaxially grown CeCoIn5 thin film.
2)Dimensional tuning of quantum criticality in CeIn3/LaIn3 and CeRhIn5/YbRhIn5
superlattices [1][2].
3)Anomalous superconductivity of two-dimensional heavy fermion in
A) CeCoIn5/YbCoIn5 superlattices [3][4][5]
B) YbCoIn5/CeCoIn5/YbRhIn5 tricolor superlattices
C) CeCoIn5/CeRhIn5 hybrid superlattices.
4) The magnetic properties of Ce- and Yb- block layers and their interface in
CeCoIn5/YbCoIn5 probed by spatially resolved NMR [6].
The heavy fermion superlattices offer a new playground for exploring exotic
superconducting phases [7].
In collaboration with R. Endo, Y. Hanaoka, K. Ishida, T. Ishii, S. Kasahara, Y.
Kasahara, M. Naritsuka, T. Terashima, Y. Tokiwa, Y. Torii, R. Toda, T. Watashige, T.
Yamanaka, (Kyoto Univ.) Y. Mizukami, T. Shibauchi, M. Shimozawa (Univ. of
Tokyo) , H. Shishido (Osaka Pref. Univ.) and S.K. Goh (Chinese Univ. of Hong
Kong)
References
[1] Science 327, 980 (2010).
[2] a preprint.
[3] Nature Physics 7, 849 (2011).
[4] Phys. Rev. Lett. 109, 157006 (2012).
[5] Phys. Rev. Lett. 112, 156404 (2014).
[6] Phys. Rev. B 92, 241105 (2015).
[7] arXiv:1601.07003.
65
Th-S13-3
Mengminwei R225
Thursday 9:30-9:45
NMR and NQR studies on heavy fermion superlattices
CeCoIn5/YbCoIn5
Takayoshi Yamanaka1, Masaaki Shimozawa2, Ryota Endo1, Yuta Mizukami3,
Hiroaki. Shishido4, Takahito Terashima5, Takasada Shibauchi1,3, Yuji Matsuda1,
Kenji Ishida1
5.
1. Department of Physics, Kyoto University. Japan
2. Institute for Solid State Physics, the University of Tokyo, Japan
3. Department of Advanced Materials Science, the University of Tokyo, Japan
4. Depertment of Physics and Electronics, Osaka Prefecture University, Japan
Research Center for Low Temperature and Materials Science, Kyoto University, Japan
Recently, the technique of fabricating epitaxial superlattices consisting of heavy
fermion (HF) compounds and conventional metals has been developed and provides
us a novel research field on f-electron systems [1, 2]. Although one of the HF
superlattices consisting of HF superconductor CeCoIn5 and conventional metal
YbCoIn5 exhibits superconductivity as bulk CeCoIn5, it shows several unusual
superconducting properties such as two dimensional superconductivity revealed by
the angle dependence of 𝐻c2, and suppression of the Pauli depairing effect [2-4]. In
the superlattices, it is considered that the heterostructure would play an important role,
but the lack of microscopic information prevent us from understanding the unusual
physical properties.
To investigate the magnetic and electronic properties in each block layer (BL) of
the superlattices, we have performed nuclear magnetic resonance (NMR)
measurement, which is one of the most suitable microscopic probes, on the
CeCoIn5/YbCoIn5 superlattices [5]. By comparing the NMR spectra of the
superlattice samples with those of single component thin films, we succeeded in
identifying the 115In-NMR signals arising from the Ce and Yb BLs in the
superlattices, separately. From the measurements of nuclear spin-lattice relaxation
rate, we found that the antiferromagnetic (AFM) fluctuations of Ce BLs are
systematically suppressed with deceasing Ce BL thickness, whereas Yb BLs remain
conventional metals. In addition, we identified 115In-NMR signals arising from the
interfaces and the inner layers and found that the suppression of AFM fluctuations is
prominent near the interface. Taking into account of these results, we suggest that the
breaking of local inversion symmetry at the interfaces plays an important role for the
suppression of the AFM fluctuations.
Currently, we strive to do nuclear quadrupole resonance (NQR) measurements on
the superlattices to investigate the superconducting properties. In my presentation, I
will show the microscopic information mentioned above, together with the ongoing
NQR results.
Reference:
[1] Science 327, 980-983 (2010).
[2] Nature Phys. 7, 849 (2011).
[3] Phys. Rev. Lett. 109, 157006 (2012).
[4] Phys. Rev. Lett. 112, 156404 (2014).
[5] Phys. Rev. B 92, 241105(R) (2015)
66
Th-S13-4
Mengminwei R225
Thursday 9:45-10:00
Topological superconductivity in noncentrosymmetric cuprate and
heavy fermion superconductors
Y. Yanase1,2, A. Daido1, T. Yoshida2,3, T. Watanabe2
2.
Graduate School of Science and Technology, Niigata University, Niigata, Japan
3. Department of Physics, Gakushuin University
We theoretically investigate various topological superconducting phases stabilized
by cooperation of unconventional Cooper pairing and spin-orbit coupling (SOC). First,
we show that a pair density wave state is stabilized by SOC in an artificial heavy
fermion superlattice CeCoIn5/YbCoIn5 [1], and it is a topological crystalline
superconducting state protected by mirror symmetry (Fig.1) [2,3]. Second, a
topological superconducting state in symmetry class D may be stabilized in a
monolayer high-temperature cuprate superconductor and CeCoIn5 [4], which have
been artificially fabricated recently [5]. Finally, we demonstrate gapless Weyl
superconducting states of new type in noncentrosymmetric heavy fermion
superconductors CeRhSi3 and CeIrSi3 [4], and in a spin-triplet superconductor UPt3
[6], by adopting a generic order parameter of superconductivity in the irreducible
representation, B1 and E2u, respectively. We discuss essential roles of the SOC arising
from
global
or
local
violation
of
inversion
symmetry.
Reference:
[1] Nat. Phys. 7, 849 (2011).
[2] Phys. Rev. Lett. 115, 027001 (2015).
[3] Phys. Rev. B 92, 174502 (2015).
[4] Phys. Rev. B (2016).
[5] Nature 472, 458 (2011).
[6] in preparation.
67
Th-S14-1
Mengminwei R139
Thursday 8:30-9:00
Symmetry, Topology, and Magnetism in Hyperhoneycomb and
Hyperkagome Iridates
Yong Baek Kim1,2
1 Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
2 Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
We discuss recent progress in theoretical understanding of emergent topological
and magnetic phases in hyperhoneycomb (beta- and gamma-Li2IrO3) and
hyperkagome (Na4Ir3O8) iridates. In particular, we derive generic spin models for
these systems in the local moment regime and investigate possible quantum spin
liquid phases and unusual magnetism. Due to the strong spin-orbit coupling, the local
moment of Ir4+ ion is described by the pseudospin Jeff=1/2 Kramers doublet that is a
combination of the spin and orbital degrees of freedom. We use the symmetries of the
lattice to deduce possible interactions between local moments and derive the
microscopic model by taking into account multiorbital interactions in combination
with the strong spin-orbit coupling. Comparison to recent experimental results on both
iridates is made and implications for future experiments are discussed.
68
Th-S14-2
Mengminwei R139
Thursday 9:00-9:30
Novel properties of 5d transition metal Compounds
Xiangang Wan
Department of Physics, Nanjing University, Nanjing China
In 5d transition metal compounds, novel properties arise from the interplay of
electron correlations and spin-orbit interactions. In this talk, we briefly review our
theoretical works relating to 5d compounds: the topological Weyl-Semimetal in
pyrochlore iridates, the Axion insulatior in spinel osmates, the Slater insulator in
perovskite osmates. We also discuss the novel properties of WTe2.
Reference:
[1] Phys. Rev. B 83, 205101 (2011).
[2] Phys. Rev. Lett. 108,146601 (2012).
[3] Phys.Rev. B 85, 174424(2012).
[4] Phys. Rev. B 91, 064104 (2015).
[5] Nature Commun. 6, 7805 (2015).
[6] Phys. Rev. Lett. 115, 166601 (2015).
69
Th-S14-3
Mengminwei R139
Thursday 9:30-9:45
Electron-Doped Sr2IrO4: An Analogue of Hole-Doped Cuprate
Superconductors Demonstrated by Scanning Tunneling Microscopy
Y. J. Yan1, M. Q. Ren1, H. C. Xu1, B. P. Xie1,2, R. Tao1, H. Y. Choi3, N. Lee3, Y. J.
Choi3, T. Zhang1,2, and D. L. Feng1,2,*
1.
2.
State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials
Laboratory, Fudan University, Shanghai 200433, China
Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai
200433, China
3. Department of Physics and IPAP, Yonsei University, Seoul 120-749, Korea
Sr2IrO4 was predicted to be a high-temperature superconductor upon electron
doping since it highly resembles the cuprates in crystal structure, electronic structure,
and magnetic coupling constants. Here, we report a scanning tunneling
microscopy/spectroscopy (STM/STS) study of Sr2IrO4 with surface electron doping
by depositing potassium (K) atoms. We find that as the electron doping increases, the
system gradually evolves from an insulating state to a normal metallic state, via a
pseudogap like phase, and a phase with a sharp, V-shaped low-energy gap with about
95% loss of density of state (DOS) at EF. At certain K coverage (0.5–0.6 monolayer),
the magnitude of the low-energy gap is 25–30 meV, and it closes at around 50 K. Our
observations show that the electron-doped Sr2IrO4 remarkably resembles hole-doped
cuprate superconductors.
Reference:
[1] PRX 5, 041018 (2015)
[2] Nat. phys. 12, 37 (2016)
[3] Science 345, 187 (2014)
70
Th-S14-4
Mengminwei R139
Thursday 9:45-10:00
The Electronic Ground State of Sr2IrO4: a Core Level Resonant
Inelastic X-ray Scattering Study
S. Agrestini,1 C.-Y. Kuo,1 M. Moretti Sala,2 Z. Hu,1 K.-T. Ko,1 P. Glatzel,2 M.
Rossi,2 J.-D.Cafun,2 K. O. Kvashnina,2 H. Takagi,3,4 L. H. Tjeng,1 and M. W.
Haverkort1
1.
Max Planck Institute for Chemical Physics of Solids, Nöthnitzerstr. 40, 01187 Dresden,
Germany
2. ESRF-The European Synchrotron, 71 Avenue des Martyrs, 38000 Grenoble, France
3. Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart,
Germany
4. Department of Physics and Department of Advanced Materials, University of Tokyo, 7-3-1
Hongo, Tokyo 113-0033, Japan
Sr2IrO4 is an insulator despite the fact that the Coulomb energy U in the 5d shell is
very small in comparison to the 5d band width. The insulating character of Sr2IrO4
has been explained in terms of a novel state, the so-called Jeff=1/2 Mott ground state,
induced by the strong spin-orbit coupling [1]. This novel Jeff=1/2 state has attracted
immense attention in the solid state community, and the interest has been even more
boosted by theoretical studies predicting the occurrence of other exotic electronic and
magnetic properties including topological insulators and quantum spin liquids.
However, how close is the real ground state in iridates to a pure Jeff=1/2 state has been
debated in literature [2].
Here we present a core level Resonant Inelastic X-ray Scattering investigation of
Sr2IrO4. We observe a clear linear dichroism between different experimental
geometries employed: the scattered intensity depends both on the incoming as well as
on the outgoing polarization. In particularly we find a strong change of the spectra
depending if the polarization is in the ab-plane or parallel to the c direction of Sr2IrO4.
Polarization dependence of RIXS is related to the low energy parameters of the
system, e.g. local crystal field and covalency, just like x-ray absorption spectroscopy.
We show how the interplay between band-formation, covalence, crystal-fields,
Hunds-rule exchange and spin-orbit coupling lead to a local doublet which indeed has
a small bandwidth and thus supports insulating behavior, but exhibits a much larger
covalent character compared to a localized atomic Jeff=1/2 state. We find the (xy) and
(xz/yz) orbitals are nearly degenerate, however, the high covalency causes the orbitals
to be very different in shape, extends and interactions, which prevent a nearest
neighbor Kitaev or other compass model to be formed.
Reference:
[1] PRL 101, 076402 (2008).
[2] PRL 112, 026403 (2014) and references therein.
71
Th-S15-1
Mengminwei R225
Thursday 10:30-11:00
Global Phase Diagram and Quantum Criticality of Heavy Fermion
Metals and Kondo Insulators
Qimiao Si1
1.
Department of Physics and Astronomy & Center for Quantum Materials, Rice University,
Houston, Texas, USA
Correlated electron systems display a variety of orders. The associated quantum
critical point is the subject of extensive current interest. Many important questions
arise. For example, how does quantum criticality nucleate non-Fermi liquid behavior
and unconventional superconductivity? How does it go beyond the Landau framework
of order-parameter fluctuations? Heavy fermion metals provide a prototype setting to
address these issues, particularly through the notion of Kondo destruction [1].
In this talk, I will report on the recent progresses in the study of a proposed global
phase diagram for heavy fermion systems; in this phase diagram, the development and
destruction of the Kondo effect as well as the magnetic ordering are tuned not only
through the RKKY-Kondo competition, but also by the quantum fluctuations of local
moments. Work along several directions will be discussed. Firstly, in the context of
heavy fermion metals near antiferromagnetic order, where the global phase diagram
was initially proposed [2], we have recently carried out concrete model studies. Here,
the quantum fluctuations we have considered are tuned either through geometrical
frustration [3] or by a transverse magnetic field in Ising-anisotropic systems [4].
Secondly, for Kondo insulators, a related global phase diagram was also proposed
some time ago [5]. Our recent model study [6] has substantiated the proposed phase
diagram and, in addition, addressed the nature of incipient Fermi surface in the Kondo
insulator state. Finally, we have recently analyzed the relevance of quadrupolar
degree of freedom in this context. In discussing these theoretical results, I will also
address their implications for a variety of heavy fermion metals and Kondo insulators.
References:
[1] Nature 413, 804 (2001).
[2] Physica B378, 23 (2006); Phys. Status Solidi B247, 476 (2010).
[3] Phys. Rev. Lett. 113, 176402 (2014).
[4] arXiv:1603.03829.
[5] J. Low Temp. Phys. 161, 233 (2010);Phys. Status Solidi B250, 425 (2013).
[6] arXiv:1509.02907.
72
Th-S15-2
Mengminwei R225
Ubiquity of Unconventional Quantum Criticality due to Critical
Valence Fluctuations in Heavy Fermion Metals
K. Miyake1 and S. Watanabe2
1 Toyota Physical and Chemical Research Institute, Nagakute, Japan
2 Department of Basic Sciences, Kyushu Institute of Technology, Kitakyushu, Japan
In the past decade or so, it gradually turned out that the critical-valence-transition
or sharp-valence-crossover phenomenon in heavy fermion metals is rather ubiquitous
than thought a decade ago. Indeed, a series of unconventional quantum critical
phenomena, which cannot be understood on the basis of the quantum criticality
associated with magnetic transitions, has been observed in YbCu5-xAlx (x=3.5) [1],
YbRh2Si2 [2], β-YbAlB4 [3], β-YbAl1-xFexB4 (x=0.014) [4], and Yb15Al34Au51 [5].
The non-Fermi liquid behaviors observed in these compounds can be explained in a
coherent way by a scenario based on the critical valence fluctuations (CVF) using
mode-mode coupling approximation for CVF [6]. The recent highlight was that the
so-called T/B scaling propery of magnetization, observed in β-YbAlB4 [3,7] and a
quasi-crystal compound Yb15Al34Au51 [5], is theoretically derived by taking into
account the effect of the magnetic field in the mode-mode coupling theory [8].
The unconventional phenomena associated with sharp valence crossover have also
been observed in a series of Ce-based heavy fermion metals since CeCu2Ge2 had been
reported to exhibit anomalous properties characteristic to the sharp valence crossover
of Ce ion under pressure [9]. After that, similar behaviors have been reported in
CeCu2Si2 [10], CeCu2Si1.08Ge0.2 [11], and CeRhIn5 [12], which can be comprehensively understood on the basis of valence crossover scenario [13]. It was also
predicted [14] that the position of the critical point of valence transition is
considerably moved by applying the magnetic field, which opens a possibility of
realizing the critical point by tuning pressure and magnetic field simultaneously.
Recently, a symptom of such a phenomenon was reported in CeCu6 [15], which is
considered to be located in the crossover region of valence transition [10,16]. This
suggests that the puzzling non-Fermi liquid properties observed in CeCu6-xAux (x~0.1)
[17] may be revisited from the viewpoint of this CVF scenario.
Reference:
[1] PRB 56, 711 (1997); C. Seuring et al., Physica B 281, 374 (2000).
[2] PRL 85, 626 (2000); K. Ishida et al., PRL 89, 107202 (2002).
[3] Nat. Phys. 4, 603 (2008).
[4] private communication.
[5] Nat. Mater. 11, 1013 (2012); private communication.
[6] PRL 105, 186403 (2010); JPSJ 82, (2013) 083704.
[7] Science 331, 316 (2011); JPSJ 84, 024710 (2015).
[8] JPSJ 83, 103708 (2014).
[9] Physica B 259–261, 1 (2008).
[10] J. Phys.: Condens. Mat. 19, 125201 (2007).
[11] PRB 69, 024508 (2004). [12] Science 302, 2104 (2003).
[13] JPSJ 83, 061006 (2014). [14] PRL 100, 236401 (2008); JPSJ 78, 104706
(2009).
[15] JPSJ 81, SB009 (2012).
[16] J. Low Temp. Phys. 120, 107 (2000).
[17] Rev. Mod. Phys. 79, 1015 (2007).
73
Th-S15-3
Mengminwei R225
Enhancement of Unconventional Superconductivity Near a Local
Quantum Crititical Point
J. H. Pixley1,2, Lili Deng3, Kevin Ingersent3, Q. Si1
2.
1. Department of Physics and Astronomy, Rice University, Houston, Texas, USA
Condensed Matter Theory Center and the Joint Quantum Institute, Department of Physics,
University of Maryland, College Park, Maryland, USA
3. Department of Physics, University of Florida, Gainesville, Florida, USA
Unconventional superconductivity is found on the border of magnetism in a wide
range of strongly correlated systems. In many cases, non-Fermi liquid behavior in the
normal state above the superconducting transition temperature is thought to arise from
a quantum critical point (QCP) hidden beneath the superconducting dome. We have
studied the role of quantum criticality in the formation of Cooper pairs within an
extended cluster dynamical mean-field theory approach to the Anderson lattice model.
The method maps the lattice to a self consistently determined problem describing two
Anderson impurities that each hybridize with a conduction band, that interact with
one another via an Ising coupling, and that are also coupled via their spin difference to
a bosonic bath representing the effect of exchange with lattice sites outside the cluster.
The numerical renormalization group and continuous-time quantum Monte Carlo
methods have been used to solve this effective problem and explore the nature of the
antiferromagnetic QCP. If the magnetic fluctuations are three-dimensional in
character, the QCP is of the conventional spin-density-wave (SDW) type where heavy
quasiparticles exist on either side of the quantum phase transition. By contrast,
two-dimensional magnetism leads to local quantum criticality where the Kondo scale
vanishes continuously on approach to the QCP from the paramagnetic side, while at
the QCP the staggered lattice susceptibility has a T-α temperature dependence with α =
0.81(4) in good agreement with the value α~0.75 observed in experiments on
CeCu6-xAux. Superconducting pairing fluctuations are significantly enhanced in the
vicinity of both types of QCPs, but at every temperature studied, the locally critical
point produces a stronger pairing enhancement than in the SDW case. Local quantum
criticality is therefore a novel and compelling mechanism for unconventional
superconductivity.
74
Th-S15-4
Mengminwei R225
Magnetic-field-induced anomalies and Lifshitz transitions in heavy
fermion materials
Gertrud Zwicknagl
Institut of. Mathematische Physik, TU Braunschweig, Braunschweig, Germany
Many heavy-fermion materials exhibit pronounced anomalies in the variation with
magnetic field of their thermodynamic and transport properties (see e. g. [1]). In
YbRh2Si2, the observed anomalies could be related to magnetic-field-induced Lifshitz
transitions, i. e., reconstructions of the Fermi surface,. [2,3]. Here, we present recent
results on the evolution with magnetic field of the Fermi surfaces in various Ce- and
Yb- based heavy-fermion compounds. The heavy quasi-particles are calculated by
means of the Renormalized Band method which explicitly accounts for the
field--dependence of the e f fect ive g-factor and of the quasiparticle mass in a Kondo
system [4]. Of particular interest is the influence of magnetic-field-induced Fermi
surface transitions on Spin Density Wave instabilities as reflected in recent neutron
scattering results.
References:
[1] Phys. Rev. B 85, 035127 (2012); M. Boukahil et al.,
Phys. Rev B 90, 075127 (2014); R.Daou et al., PRL 96, 026401 (2006)
[2] Phys. Rev. Lett. 110, 256403 (2013); H. R. Naren et al,
New J. Phys. 15, 093032 (2013)
[3] J. Phys. Soc. Jpn. 82 , 053704 (2013)
[4] J. Phys.: Condens. Matter 23, 094215 (2011)
75
Th-S15-5
Mengminwei R225
Self-Consistent Renormalization Group for Kondo Screening and
Breakdown in Dense Kondo Systems
Ammar Nejati1, Katinka Ballmann1, Johann Kroha1,2
1 Physikalisches
Institut and Bethe Center for Theoretical Physics, University of Bonn, Germany
for Correlated Matter, Zhejiang University, Hangzhou, China
2 Center
The conditions for breakdown of Kondo quasiparticles near a heavy-fermion
quantum phase transition are still a controversial issue. We present a renormalization
group (RG) theory for the breakdown of Kondo screening in multi-impurity Kondo
systems with spin exchange coupling J, but without direct inter-impurity dipole
coupling and without pre assumptions about magnetic ordering or Fermi surface
criticality. Kondo singlet formation is signaled by the RG divergence of the
spin-scattering vertex  of conduction electrons from a local spin. It occurs at the
Kondo screening scale TK. In a multi-impurity system,  at a reference Kondo site i
acquires non-local contributions from conduction electrons scattering at surrounding
Kondo impurities, j ≠ i, and transferring the spin-flip to site i via the RKKY
interaction. This process involves the dynamical, local spin response  of the
surrounding Kondo sites. Since, at low energies, = (gμB)2W/TK is inversely
proportional to TK, the RKKY contributions imply a parametrical dependence of the
β-function on the system‟s Kondo scale itself. Hence, TK(y) is self-consistently
determined by the RG divergence and depends on the dimensionless RKKY coupling
parameter y. As a consequence, we find a universal suppression of the local
spin-screening scale TK(y) in Kondo lattice and multi-impurity systems. Kondo singlet
formation eventually ceases to exist beyond a maximum RKKY coupling ymax,
where ymax is a universal function of the bare (single-impurity) scale TK(y=0). At the
breakdown point, TK(ymax) remains finite and assumes the universal value
TK(ymax)/TK(0) = 1/e ≈ 0.368 [1]. For y>ymax, the RG is non-divergent, i.e., TK(y) is no
longer defined. We confirmed that for all values of y and of TK(0) the RG flow
remains in the perturbatively controlled regime. The local screening scale TK(y) is
experimentally observable as the resonance width of local Kondo spectra. It is found
to be in remarkable, quantitative agreement with STM spectroscopy on tunable
two-impurity Kondo systems [2].
For two-quantum-dot (Qdot) systems with unequal Kondo couplings, J1, J2, J1<J2,
we find an exponentially strong suppression of TK1(y) in the weaker coupled Qdot 1 as
compared to the stronger coupled Qdot 2. Hence, the conductance of Qdot 1 can be
sensitively switched between the Kondo and the Coulomb-blockade regimes by the
coupling of Qdot 2, in consistency with experiments [3].
References:
[1] preprint (2016).
[2] Nature Physics 7, 901 (2011).
[3] Phys. Rev. B 83, 241308(R) (2011).
76
Th-S16-1
Mengminwei R139
Superconductivity in weakly correlated noncentrosymmetric systems
F. Kneidinger1, I. Zeiringer2, P. Rogl2, C. Blaas-Schenner3, D. Reith3, R. Podloucky3,
E. Bauer1
1. Institute of Solid State Physics, Vienna University of Technology, A-1040 Wien, Austria.
2. Institute of Physical Chemistry, University of Vienna, A-1090 Wien, Austria.
3. Institute of Physical Chemistry, University of Vienna and Center for Computational
Materials Science, A-1090 Wien, Austria.
Superconductivity in absence of inversion symmetry of the crystal structure is
basically controlled by a Rashba-like antisymmetric spin orbit coupling which splits
the Fermi surface and removes the spin degeneracy of electrons. The Fermi surface
splitting can originate a mixing of spin-singlet and spin-triplet states in the
superconducting condensate. The presence of spin-triplet states is expected to be
responsible for various uncommon features of the superconducting ground state.
Experimentally, distinct deviations from the expectations of the BCS theory are found,
in general, only in those systems where besides the missing of inversion symmetry
strong correlations among electrons are present. Materials of this group are primarily
based on Ce, Yb or U. The present work intends to comprehensively map the much
larger group of materials without substantial electronic correlations and classifying
their superconducting properties with respect to broken symmetries, experimental data
and DFT ab-intio derived results.
Work supported by the Austrian FWF P22995.
77
Th-S16-2
Mengminwei R139
Noncentrosymmetric superconductivity in a clean crystal of type –II
superconductor BiPd
S. Ramakrishnan, Bhanu Joshi and Arumugam Thamizhavel
Department of Condensed Matter Physics, Tata Institute of Fundamental Research, Homi Bhabha
Road, Mumbai-400005, India
In this talk I will elucidate[1] the bulk superconductivity of a high-quality single
crystal of monoclinic BiPd (-BiPd, space group P21) below 3.8 K by studying its
electrical resistivity, magnetic susceptibility, and heat capacity. This is the cleanest
noncentrosymmetric superconductor that display anisotropy due to spin-orbit
scattering and also exhibits unusual superconducting properties due to s and p wave
mixing as evidenced by the observation of Andreev bound state and multiple energy
gaps via point contact measurements[2]. In addition, Fermi surface studies suggest
multiband superconductivity in this compound[3]. Penetration depth studies[4] and
NQR[5] investigations support mixing of s and p wave Copper paring in this crystal.
Moroever, Muon spin rotation measurements indicate[6] strong field dependence of
the Ginzburg Landau coefficient of this superconductor. Recent works on unusual
normal state (Dirac cones) properties of BiPd will also be discussed.
References
[1] Bhanu Joshi, A. Thamizhavel, and S. Ramakrishnan, Phys. Rev. B 84, 064518
(2011).
[2] Mintu Mondal, Bhanu Joshi, Sanjeev Kumar, Anand Kamlapure, Somesh Chandra
Ganguli, Arumugam Thamizhavel, Sudhansu S. Mandal,
Srinivasan
Ramakrishnan,and Pratap Raychaudhuri, Phys. Rev. B 86, 094520 (2012).
[3] To be published.
[4] L. Jiao, J. L. Zhang, Y. Chen, Z. F. Weng, Y. M. Shao, J. Y. Feng, X. Lu, B. Joshi,
A. Thamizhavel, S. Ramakrishnan, and H. Q. Yuan, Phys. Rev. Rapid Comm. B 89,
060507(R) (2014).
[5] Kazuaki MATANO, Satoki MAEDA, Hiroki SAWAOKA, Yuji MURO, Toshiro
TAKABATAKE, Bhanu JOSHI, Srinivasan RAMAKRISHNAN, Kenji
KAWASHIMA, Jun AKIMITSU and Guo-qing ZHENG, Journal of the Physical
Society of Japan 82, 084711 (2013).
[6] To be published.
78
Th-S16-3
Mengminwei R139
Superconductivity and Dirac surface states in non-centrosymmetric
BiPd studied by STM/STS
Zhixiang Sun1, Mostafa Enayat1, Ana Maldonado Cid1,2, Calum Lithgow2, Ed
Yelland2, Darren C. Peets1, Alexander Yaresko1, Andreas P. Schnyder1, Peter
Wahl1,2
1. Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
2. School of Physics and Astronomy, University of St Andrews, United Kingdom
In most known superconductors, inversion symmetry and Pauli exclusion ensure
that the Cooper pair wave function can be separated into an orbital component that
has either even or odd parity, and a spin component which is then either singlet or
triplet, but this does not hold in general. Absent of an inversion center in the crystal
structure, parity is not a good quantum number, and the pairs will be some mixture of
singlet and triplet. We report ultra-low temperature scanning tunneling
microscopy/spectroscopy (ULT-STM/STS) measurements at temperatures down to 15
mK on the recently rediscovered non-centrosymmetric superconductor α-BiPd [1].
While samples can be prepared with a high quality surface, allowing for atomic
resolution imaging, tunneling spectra recorded at temperatures well below Tc show
only a single superconducting gap with Δ0 = 0.6 meV. The temperature and magnetic
field dependence of the gap are found to be well described by BCS theory and a single
s-wave gap. Our results provide an upper limit for a possible triplet component in
α-BiPd of 10μeV [2].
While results from scanning tunneling spectroscopy are fully consistent with
specific heat, transport shows additional transitions at a higher magnetic field
compared to the bulk Hc2. Possible origins of these anomalies are discussed.
Our spectroscopic data, combined with calculations, reveal evidence for Dirac-like
surfaces states, which are non-equivalent on the two opposite faces of the material.
References:
[1] B. Joshi, A. Thamizhavel and S. Ramakrishnan, Phys. Rev. B 84, 064518 (2011).
[2] Z. Sun, et al., Nat. Commun. 6, 6633 (2015)
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Mengminwei R139
BaNiS2 : a semi-metal with strong Rashba coupling
David Santos-Cottin1, Michele Casula1, Gabriel Lantz2, Yannick Klein1, Luca
Petaccia3, Patrick Le Fèvre4, François Bertran4, Evangelos Papalazarou2, Marino
Marsi2, Andrea Gauzzi1
1. IMPMC, UniversitéPierrePierre et Marie Curie, Paris, France
2. Laboratoire de Physiques des Solides, UniversitéParis-Sud, Orsay, France
3. Elettra Sincrotrone Trieste,Trieste, Italy
4. Synchrotron SOLEIL, Gif-sur-Yvette, France
The research for spintronics applications asks for new materials where spin-orbit
coupling induces non trivial electronic states. A promising mechanism that offers this
possibility is the Rashba effect, arising from the spin-orbit coupling in an asymmetric
potential, because it splits the bands with opposite spin chirality [1]. Strong Rashba
splittings have been found either in non-centrosymmetric bulk crystals made of heavy
elements [2], where spin-orbit coupling is intrinsically large, or at surfaces where
strong electric fields may exist [3]. By a combination of ARPES measurements and
band calculations in the DFT approximation we found a very large Rashba coupling
αR ≈ -0.25 eV Å in BaNiS2 semi-metal, a centrosymmetric system composed of
comparatively light elements. The energy splitting associated to the Rashba coupling
is as large as Δε ≈ -150 meV. This surprising result finds its origin in a peculiar
square-pyramidal network responsible for a huge staggered crystal field ≈ -1.4 V/Å
that breaks the local inversion symmetry at the Ni site. Our study demonstrates that
the Rashba coupling can be amplified, without the restriction of using either heavy
elements or surfaces, if the symmetry of the crystal is mastered, and opens a new
strategy for finding applications in the growing field of spin-orbit band engineering.
Reference:
[1] R. Winkler, Spin-orbit Coupling Effects in Two-Dimensional Electron and Hole
Systems, vol. 191 of Springers Tracts in Modern Physics, (Spinger-Verlag Berlin
Heidelberg, 2003).
[2] K. Ishizaka et al., Nature Materials 10, 521 (2011).
[3] A. F. Santander-Syro et al., Nature Materials 13, 1085 (2014).
80
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Mengminwei R139
Time-reversal symmetry breaking in La7Ir3 revealed by muon-spin
relaxation
J. A. T. Barker1, D. Singh2, A. Thamizhavel3, A. D. Hillier4, M. R. Lees1, G.
Balakrishnan1, D. McK. Paul1, and R. P. Singh2.
1. Physics Department, University of Warwick, Coventry, CV4 7AL, United Kingdom
2. Department of Physics, Indian Institute of Science Education and Research Bhopal,
Bhopal-462066, India
3. Department of Condensed Matter Physics and Materials Science, Tata Institute of
Fundamental Research, Mumbai 400005, India
4. ISIS facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation
Campus, Oxfordshire, OX11 0QX, United Kingdom
It is well known that the transition to the superconducting phase spontaneously
breaks global gauge symmetry, yet it is possible for other symmetries to be broken as
well. In noncentrosymmetric materials, the lack of inversion symmetry in the crystal
structure allows an admixture of spin-singlet and spin-triplet superconducting
channels to exist, due to the formation of an anti-symmetric spin-orbit coupling.
Recently, muon spin relaxation measurements revealed broken time-reversal
symmetry in La7Ir3. The detection of time-reversal symmetry breaking in a
superconducting system is strong evidence that the superconducting ground state
contains a spin-triplet component. However, measurements of the superfluid density
reveal a fully-gapped, isotropic order parameter. Unlike previous discoveries, this
material has a hexagonal crystal structure, and thus opens a new avenue of potential
theoretical and experimental investigations.
References
[1] J. A. T. Barker et al., PRL 115, 267001 (2015)
81
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Mengminwei R225
Nuclear Magnetic Resonance (NMR) and Nuclear Quadruple
Resonance (NQR) Studies on Sr2RuO4
K. Ishida,1 M. Manago,1 Z. Q. Mao,1# Y. Maeno1 and K. Miyake2
1. Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502,
Japan
2. Toyota Physical and Chemical Research Institute, Nagakute, Aichi 480-1192, Japan
We have measured 99Ru and 17O NMR Knight-shift above µ0H~0.9T after the
recent reportsof the first order transition near Hc2 [1,2]. We found no shift nor
broadening of the NMR spectra of both 99Ru and 17O in the field region where the first
order was reported. Our results suggest that the origin of the first-order transition is
not ascribed to the Pauli-depairing effect, but to the other effects including the orbital
degree of freedom. On the other hand, we found that the spin susceptibility
originating from the Ru-4d electron slightly increases by ~ 2 % of the total and
becomes inhomogeneous in the superconducting(SC) state [3]. These are reasonably
explained if the electron pairs from the equal-spin pairing(ESP)in the SC mixed
state.We suggest that the extra magnetization in the superconducting state is a new
phenomenon specific to the ESP in spin-triplet superconductivity.
In addition, I will show the recent result of the nuclear spin-spin relaxation rate
(1/T2) in the SC state, which suggests the presence of the magnetic fluctuations along
the c axis in the SC state.
#Present address: Department of Physics, Tulane University, New Orleans L.A. USA
Reference:
[1] S. Yonezawa, T. Kajitani, and Y. Maeno, Phys. Rev. Lett. 110, 077003 (2013).
[2] S. Kittaka, et al. Phys. Rev. B 90, 220502 (R)
[3] K. Ishida et al. Phys. Rev. B 92, 1005002 (R)
82
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Mengminwei R225
Strain-Tuning of the Ruthenates Sr2RuO4 and Sr3Ru2O7
Clifford W. Hicks1, M.E. Barber1,2, D.O. Brodsky1,2, A. Steppke1,2, L. Zhao1,2, R.S.
Perry3, A.S.Gibbs4, S. Yonezawa5, Y. Maeno5, A.P. Mackenzie1,2
1. Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
2. University of St Andrews, St Andrews, United Kingdom
3. University College London, London, United Kingdom
4. Max Planck Institute for Solid State Research, Stuttgart, Germany
5. Kyoto University, Kyoto, Japan
The introduction of piezoelectric-based uniaxial pressure cells has allowed higher
uniaxial pressure to be achieved then previously, and with precise in situ tunability. It
has proven especially useful for study of the ruthenates Sr2RuO4 and Sr3Ru2O7.
Sr3Ru2O7 has an anomalous phase associated with proximity to a metamagnetic
quantum critical endpoint. Lifting the near-tetragonal symmetry of the unstrained
lattice appears to shift the relative magnitudes of (100)- and (010)-oriented density
waves within this phase; the phase responds strongly to symmetry-breaking fields, but
in a manner more consistent with microscopic coexistence than the spontaneous C4
symmetry breaking that has long been suspected in Sr3Ru2O7. Lifting the tetragonal
symmetry of unstrained Sr2RuO4, on the other hand, was expected to split the
transition temperatures of the px and py components of a px±ipy superconducting order
parameter. Whether this happens or not is still under investigation, but what certainly
occurs with orthorhombic distortion is a strong increase in Tc, and very strong
enhancement of Hc2; implications for the symmetry of the order parameter will be
discussed.
83
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Mengminwei R225
Controlling Emergent Ground States in Ruthenate Thin Films
through Epitaxial Strain and Quantum Confinement
Kyle M. Shen1, Bulat Burganov1, Yang Liu1,2, Carolina Adamo1,3, Hari P. Nair1, and
Darrell G.Schlom1.
1. Departments of Physics and Materials Science & Engineering, Cornell University, USA
2. Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou,
China
3. Department of Applied Physics, Stanford University, USA
The ruthenates host a wide array of emergent properties, from spin-triplet
superconductivity, quantum criticality, metamagnetism, ferromagnetism, and
antiferromagnetism. Here, we report how we can control these emergent properties
and their electronic structure in thin films grown by molecular beam epitaxy through
epitaxial strain and stabilization and quantum confinement. We demonstrate how a
Lifshitz transition can be driven via epitaxial strain in the spin-triplet superconductor
Sr2RuO4, leading to quantum critical fluctuations at the critical point. We also show
how epitaxial stabilization and quantum confinement can be used to control
ferromagnetism in thin films of the perovskite ruthenates CaRuO3, SrRuO3, and
BaRuO3.
84
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Mengminwei R225
Spin density wave order and quantum critically in Sr3Ru2O7 studied
by neutron scattering
1
2
3
1
4
4
4
C. Lester , S. Ramos , R. S. Perry , T. P. Croft , R. I. Bewley , T. Guidi , P. Manuel ,
4
5
D. D. Khalyavin , E. M. Forgan , S. M. Hayden
1
1. H. H. Wills Physics Laboratory, University of Bristol, Bristol, BS8 1TL, United Kingdom.
2. School of Physical Sciences, University of Kent, Canterbury, CT2 7NH, United Kingdom.
3. London Centre for Nanotechnology and Department of Physics and Astronomy,
University College London, London WC1E 6BT, United Kingdom.
4. ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United
Kingdom.
5. School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT,
United Kingdom.
The quasi-2D metamagnetic perovskite metal Sr3Ru2O7 has been an enigma for the
last decade. The application of a large magnetic field of ~8T parallel to the c-axis
creates a new phase at low temperatures. This phase shows “electronic nematic”
properties in that strong anisotropy its resistivity can be created by tilting the field
away from the c axis. In addition, measurement of transport and thermodynamic
properties suggest that the phase is at the centre of a quantum critical region. Here we
use neutron scattering to show that the magnetic field induces spin-density-wave
magnetic (SDW) order in the proximity of a metamagnetic critical endpoint. Sr3Ru2O7
can be tuned through two magnetically-ordered SDW states which exist over
relatively small ranges in field (< 0.4 T). Their origin is probably due to the electronic
fine structure near the Fermi energy. The magnetic field direction is shown to control
the SDW domain populations which naturally explains the strong resistivity
anisotropy or electronic nematic behaviour observed in this material. We find that
Sr3Ru2O7 is also unique in that its quantum critical region is controlled by
overdamped incommensurate low energy spin fluctuations with a diverging relaxation
time. The low-energy electronic properties reflect the presence of these fluctuations
and, in particular, the field dependent low-temperature specific heat is proportional to
the spin relaxation rate.
Reference
[1] C. Lester, at el. Natural Materials 14, 373 (2015).
85
Th-S18-1
Mengminwei R139
Quantum Criticality driven by Frustration
Philipp Gegenwart
Center for Electronic Correlations and Magnetism, University of Augsburg, Germany
Frustrated magnetism has become an active field of research due to various novel
states such as gapped or gapless spin liquids, spin nematics, or spin ice, which are
different from ordinary dipolar order. A strong influence of geometrical frustration is
also discussed in the context of quantum phase transitions in Kondo metals, because
quantum fluctuations arising from frustrated interactions are counter-acting Kondo
singlet formation. I will present results on the geometrically frustrated Kondo lattice
CeRhSn [1], where the Kondo ions are located on distorted Kagome planes stacked
along the c-axis. Thermal expansion proves a novel quantum critical state which is
related to the geometrical frustration. We also discuss the change of the ground state
under uniaxial pressure.
Work in collaboration with Y. Tokiwa, R. Küchler, C. Stingl, M.-S. Kim and T.
Takabatake. Financial support by the German Science Foundation through project
GE1640/8-1 is gratefully acknowledged.
Reference:
[1] Y. Tokiwa, C. Stingl, M.-S. Kim, T. Takabatake, P. Gegenwart: Characteristic
signatures of quantum criticality driven by geometrical frustration. Sci. Adv. 1, (2015)
e1500001.
86
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Mengminwei R139
Quantum Criticality and Superconductivity in Icosahedral
Quasicrystals and Approximants with Tsai-type Clusters
K. Deguchi1, S. Matsukawa1, K. Imura1, N. K. Sato1, T. Ishimasa2
1. Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi
464-8601, Japan
2. Division of Applied Physics, Graduate School of Engineering, Hokkaido University,
Sapporo 060-8628, Japan
Quasicrystals possess long-range, quasi-periodic structures with diffraction
symmetries forbidden to crystals. Recently, a new type of icosahedral Yb quasicrystal
and approximant was discovered [1]: the Au-Al-Yb quasicrystal exhibits novel
quantum critical behavior as observed in Yb-based heavy fermion materials with
intermediate Yb valence, while the Au-Al-Yb approximant shows heavy Fermi liquid
behavior [2]. Since the diverging behavior of the magnetic susceptibility as T → 0
was only observed in the quasicrystal, the quantum critical state might correspond to
an electronic state unique to the quasicrystals. Furthermore, quantum critical
phenomenon of the Au-Al-Yb quasicrystal is remarkably robust against hydrostatic
pressure. By contrast, the Au-Al-Yb approximant shows heavy fermion behavior,
very sensitive to hydrostatic pressure and quantum criticality of the approximant is
induced by pressure. For superconductivity, there are a few reports of
superconductivity in the quasicrystals to the best of our knowledge. We have found
superconductivity of icosahedral Yb approximants by the substitution of Al atoms to
Ge atoms in Au-Al-Yb alloys [3]. Until very recently, quantum criticality and
superconductivity has been intensively studied in only crystalline materials: for
example, heavy fermion compounds. Interestingly, quantum criticality of the
Au-Al-Yb quasicrystal seems to be closely related to heavy fermion crystalline
compound β-YbAlB4 with intermediate Yb valence [4,5]. Quantum criticality,
including the T/B scaling of the thermodynamic quantities, and superconductivity in
icosahedral Yb quasicrystals and approximants will be presented and discussed.
Reference:
[1] T. Ishimasa, Y. Tanaka, and S. Kashimoto, Phil. Mag. 91, 4218 (2011).
[2] K. Deguchi, S. Matsukawa, N. K. Sato, T. Hattori, K. Ishida, H. Takakura, and T.
Ishimasa, Nature Materials 11, 1013 (2012).
[3] K. Deguchi, M. Nakayama, S. Matsukawa, K. Imura, K. Tanaka, T. Ishimasa, and
N. K. Sato, J. Phys. Soc. Jpn. 84, 023705 (2015).
[4] S. Nakatsuji, K. Kuga, Y. Machida, T. Tayama, T. Sakakibara, Y. Karaki, H.
Ishimoto, E. Pearson, G. G. Lonzarich, H. Lee, L. Balicas, and Z. Fisk, Nature
Physics 4, 603 (2008).
[5] Y. Matsumoto, S. Nakatsuji, K. Kuga, Y. Karaki, N. Horie, Y. Shimura, T.
Sakakibara, A.H. Nevidomskyy, and P. Coleman, Science 331, 316 (2011).
87
Th-S18-3
Mengminwei R139
Quantum criticality in 4f vs 3d electron systems
Emilia Morosan
Rice University Houston TX 77005 USA
The different facets of quantum criticality are well illustrated by a comparison of 4f
and 3d electron physics. In this talk I will focus on electron and hole doping In
Itinerant anti- and ferro-Magnets(IMs) without magnetic elements, followed by a brief
contrast with Yb and Ce based heavy fermion materials. The two itinerant
ferromagnetic metals without magnetic elements Sc3In[1] and ZrZn2[2] display quite
different behavior both in the ordered state and in the proximity of their respective
quantum critical points (QCPs): mean field vs. non-mean field behavior, Fermi or
non-Fermi liquid behavior etc. By contrast, the itineran t antiferromagnetic metal with
no magnetic elements, TiAu[3], has traits of a non-Fermi liquid with complex
electronic transport behavior close to its QCP. Although the physics are substantively
different, these IMs are not entirely distinct from their 4f counterparts. I will illustrate
this latter point with a few example s of Yb and Ce based heavy fermion quantum
critical systems.
[1] E Svanidze et al., PRX, 5, 01102(2015)
[2] C. Pfleiderer et al., JMMM 226-230 258(2001); D.Sokolov et al., PR 96116404
(2006)
[3] E.Svanidze et al., Nature Commun. 6,7701(2015)
88
Th-S18-4
Mengminwei R139
Magnetism and quantum criticality in the new family of heavy
fermion compounds Ce2MAl7Ge4 (M=Co, Ni, Pd, Ir)
E. D. Bauer,1 N. A. Wakeham,1 D. Kim,1 N. J. Ghimire,1 S. K. Cary, 2 S. Eley,1 P. F.
S. Rosa,1 T. Albrecht-Schmitt,2 M. Janoschek,1 C. M. Brown,3 L. Civale,1 F.
Ronning,1 R. Movshovich,1 and J. D. Thompson1
1. Los Alamos National Laboratory, Los Alamos, NM
2. Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL
3. National Institute of Standards and Technology, Center for Neutron Research,
Gaithersburg, MD
Ce-based intermetallic compounds exhibit a variety of interesting ground states
including magnetic order, heavy fermion behavior, unconventional superconductivity,
and non-Fermi liquid behavior. When magnetic order is suppressed to T= 0 K, or
quantum critical point, by chemical substitution, pressure, or magnetic field, a dome
of unconventional superconductivity is often found. Close to the quantum critical
point, non-Fermi liquid temperature dependencies of the thermodynamic and transport
properties are observed. Recently, a new family of tetragonal Ce2MAl7Ge4 (M=Co, Ni,
Pd, Ir) compounds was discovered, which crystallize in the tetragonal space group
P-421m. While the Ce2MAl7Ge4 (M=Co, Ir, Ni) materials order magnetically between
Tm = 0.8 – 1.6 K, Ce2PdAl7Ge4 exhibits non-Fermi liquid behavior at low temperature
with γ ~ 1000 mJ/mol-K2. Here, we present the structural and physical properties of
the Ce2MAl7Ge4 (M = Co, Ir, Ni, Pd) compounds and discuss the quantum criticality
in Ce2PdAl7Ge4.
89
Th-S18-5
Mengminwei R139
CePdAl - a frustrated Kondo lattice at a quantum critical point
V. Fritsch1,2, A. Sakai1, Z. Huesges3, S. Lucas3, W. Kittler2, C. Taubenheim2, K.
Grube2, C.-L. Huang2,3, P. Gegenwart1, O. Stockert3 and H. v. Löhneysen2
1. Experimental Physics VI, Center for Electronic Correlations and Magnetism, Institute of
Physics, University of Augsburg, 86135 Augsburg
2. Karlsruhe Institute of Technology, Germany,
3. Max Planck Institute for the Chemical Physics of Solids, Dresden, Germany
CePdAl is one of the rare frustrated Kondo lattice systems that can be tuned across
a quantum critical point (QCP) by means of chemical pressure, i. e., the substitution
of Pd by Ni [1]. The Kondo effect, with the incipient delocalization of the magnetic
moments, is not beneficial for the formation of a frustrated state. On the other hand,
magnetic frustrated exchange interactions between the local moments can result in a
breakdown of Kondo screening [2]. Thus magnetic frustration and Kondo effect are
antithetic phenomena. Furthermore, there is no simple observable to quantify the
degree of frustration, making the evolution of frustration an elusive parameter, when
approaching the QCP. We present thermodynamic and neutron scattering experiments
on CePd1-xNixAl around the critical concentration x ≈ 0.14 and discuss the impact of
the frustration on the critical properties.
References:
[1] V. Fritsch et al., PRB 89, 054416 (2014).
[2] T. Senthil et al. PRB 69, 035111 (2004).
90
Th-S19-1
Mengminwei R225
Temperature-dependent electronic structure evolution and
band-dependent hybridization in CeCoIn5 and CeRhIn5
Qiuyun Chen1, Kevin Huang1, Lei Shu1, Y. J. Zhang2, H. Lee2, Stefan Kirchner2,
Huiqiu Yuan2, Donglai Feng1
1.
2.
Department of Physics and State Key Laboratory of Surface Physics, Fudan University,
Shanghai, China
Center for Correlated Matter and department of Physics, Zhejiang University, Hangzhou,
China
We report the three dimensional electronic structure of CeCoIn5 by bulk-sensitive
soft x-ray angle-resolved photoemission spectroscopy. Ce 4d-4f resonant
photoemission spectroscopy was also carried out to study the 4f electronic
characteristics. Moreover, temperature-dependent measurements have been performed
from below TK (10 K) to far above (190 K), and demonstrate that the f electron is
dominated by localized character at high temperature and it starts to hybridize with
the conduction electrons at around 150 K. The hybridization is enhanced at lower
temperature and shows band-dependent. Enlargement of the electron-like pocket
around the Brillouin zone corner can be observed when f electron participates in the
Fermi surface construction. We also found anomalous temperature dependence of the
quasiparticle lifetime and band dispersion that are directly related to the transition
from incoherent to coherent f electrons upon cooling. A comparative study of
CeRhIn5 is also presented.
91
Th-S19-2
Mengminwei R225
Emergence of anisotropic heavy fermions in antiferromagnetic
Kondo lattice CeIn3 revealed by photoemission
Yun Zhang1,2,3, Haiyan Lu1, Xiegang Zhu1, Shiyong Tan1, Qiuyun Chen1, Wei Feng1,
Donghua Xie1, Lizhu Luo1, Zhengjun Zhang3, Xinchun Lai1*
1.
Science and Technology on Surface Physics and Chemistry Laboratory,
Mianyang 621907,China
2. Department of Engineering Physics, Tsinghua University, Beijing 100084, China
3. School of Materials Science and Engineering, Advanced Materials Laboratory,
Tsinghua University, Beijing 100084, China
In this work, we show kz-dependent and multi-orbital nature of the electronic
structure of antiferromagnetic heavy fermions compound CeIn3 by soft x-ray angle
resolved photoemission spectroscopy at 13K. In the vicinity of the Fermi level, the
Kondo resonance peak, which hybridizes with conduction band, and its spin orbit
coupling replica band were observed directly. Scanning the first Brillouin zone, we
find that f bands contribute to the Fermi surface greatly, implying the large Fermi
surface trait In addition, the hybridization strength between f electrons and conduction
band show slight and regular anisotropy in K space. This work illuminates the
concomitant and competitive relations of Kondo screening scenario and
Ruderman-Kittel-Kasuya-Yosida interaction and supplies some evidences for the
anisotropic superconductivity of CeIn3.
92
Th-S19-3
Mengminwei R225
Probing 5f electronic hybridization in Uranium compounds via x-ray
magnetic circular dichroism
R. D. dos Reis1, 2, L. S. I. Veiga1, 2, D. Haskel3, J. C. Lang3, Y. Joly4, 5, F. G. Gandra2,
and N. M.Souza-Neto1, 3
2.
1. Brazilian Synchrotron Light Laboratory (LNLS), Campinas, SP 13083-970, Brazil
Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas (UNICAMP), SP,
Brazil
3. Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, U.S.A.
4. Univ. Grenoble Alpes, Inst. NEEL, F-38042 Grenoble, France
5. CNRS, Inst. NEEL, F-38042 Grenoble, France
We study the spin-dependent electronic structure of UTe and UT2Si2 (T=Cu and
Mn) compounds with a combination of x-ray magnetic circular dichroism
measurements and first principle calculations. By exploiting the presence of sizable
quadrupolar and dipolar contributions to the U L2,3-edge x-ray absorption cross
section we are able to provide unique information on the extent of hybridization
between 5f and 6d/3d electronic states, a key parameter regulating the physical
properties of all actinide materials. Since this information is hardly accessible to other
probes, the new methodology opens up new venues for investigating this important
class of materials.
93
Th-S19-4
Mengminwei R225
Consistency of ARPES and dHvA for Surface States of SmB6
J. D. Denlinger1, Sooyoung Jang1,2, G. Li3, Kai Sun3, J. W. Allen3, D.-J. Kim4, Z.
Fisk4, Lu Li3
1. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
2. Department of Physics, Pohang University of Science and Technology, Pohang, Korea
3. Department of Physics, University of Michigan, Ann Arbor, MI, USA
4. Department of Physics, University of California, Irvine, CA, USA The mixed valent
compound
SmB6 is of high current interest as the first candidate example of topologically
protected surface states in a strongly correlated insulator and also as a possible host
for an exotic bulk many-body state that would manifest properties of both an insulator
and a metal [1]. Two different de Haas van Alphen (dHvA) experiments [1,2] have
each supported one of these possibilities, while angle resolved photoemission
spectroscopy (ARPES) for the (001) surface has supported the first, but without
quantitative agreement to the dHvA results. We present new ARPES data for the (110)
surface and a new analysis of all published dHvA data and thereby bring ARPES and
dHvA into substantial consistency around the basic narrative of two dimensional
surface states [3].
Reference:
[1] B. S. Tan et al., Science 349, 6245 (2015)
[2] G. Li et al., Science 346, 1208 (2014)
[3] J. D. Denlinger et al., arXiv:1601.07408 (2016)
94
Th-S19-5
Mengminwei R225
Non-Trivial Metallic Surface State of a Kondo Semiconductor YbB12
K. Hagiwara1, Y. Ohtsubo1,2, M. Matsunami3, S. Ideta3, K. Tanaka3, J. Rault4, P. Le
Fèvre4, F, Bertran4, A. Taleb-Ibrahimi4, R. Yukawa5, M. Kobayashi5, K. Horiba5,
H.Kumigashira5, F. Iga6, H. Miyazaki7, T. Ito8, S. Kimura1,2
1.
7.
Department of Physics Osaka University, Japan;
2. FBS, Osaka University, Japan;
3. IMS, Japan;
4. Synchrotron SOLEIL,France;
5. PF, KEK, Japan;
6. Department of Physics, Ibaraki University, Japan;
Department of Frontier Materials, Nagoya Institute of Technology, Japan;
8. Department of Materials Engineering, Nagoya University, Japan
Ytterbium dodecaboride YbB12 is one of Kondo insulators/semiconductors (KIs),
which have a tiny energy gap owing to the hybridization between conduction and
localized 4f electrons, namely c-f hybridization [1]. Although the bulk energy gap is
fully opened [2], the electrical resistivity is saturated at lower temperature than 10 K.
The origin of the saturation is expected to be a topologically protected metallic
surface state, namely “topological Kondo insulator” [3]. To elucidate the origin of the
metallic conduction at the surface, we performed the angle-resolved photoemission
spectroscopy of a well-defined surface of YbB12. As a result, not only the surface
metallic state but also the surface c-f hybridization state has been observed. The
surface metallic state is considered to originate from a topological state owing to the
c-f hybridization.
[1] F. Iga et al., JMMM 177–181, 337 (1998).
[2] H. Okamura et al., JPSJ 74, 1954 (2005).
[3] M. Dzero et al., PRL 104, 106408 (2010).
95
Th-S20-1
Mengminwei R139
Correlated electrons in nonequilibrium
Marcus Kollar1
1.
Theoretical Physics III, University of Augsburg, Augsburg, Germany
When an isolated quantum many-body system is forced out of equilibrium by a
sudden change in the Hamiltonian, relaxation to the thermal state predicted by
statistical mechanics should take place, as observed, e.g. in the fermionic Hubbard
model [1]. For time-periodic driving, on the other hand, heating up to infinite
temperatures is expected. Integrable systems usually show a different behavior:
because of their large number of constants of motion they remain in a nonthermal
steady state after a sudden change, or show nontrivial periodic behavior in the case of
driving [2]. A special situation arises for weakly interacting systems: due to the
proximity of an integrable, noninteracting Hamiltonian they can at first be trapped in a
so-called prethermalized state before relaxing [3], which is again due to a large
number of approximate constants of motion and can be characterized by a generalized
Gibbs ensemble [4]. For periodic driving a quasi-periodic time evolution can also
emerge, provided the driving frequency lies outside the single-particle band, with an
analogous generalized statistical description [5]. Numerical simulations for the driven
Hubbard model with nonequilibrium dynamical mean-field theory [6] show a clear
separation of the timescales for synchronization and the eventual approach to the
infinite-temperature state.
References:
[1] M. Eckstein et al., PRL 103, 056403 (2009); PRB 81, 115131 (2010)
[2] A. Lazarides et al., PRL 112, 150401 (2014)
[3] M. Moeckel and S. Kehrein, PRL 100, 175702 (2008)
[4] M. Kollar et al., PRB 84, 054304 (2011)
[5] E. Canovi et al., arXiv:1508.00991, PRB, in press
[6] H. Aoki et al., RMP 86, 779 (2014)
96
Th-S20-2
Mengminwei R139
Magnetic Phases of the Kondo Lattice
Peter S Riseborough1
1.
Physics Department, Temple University, Philadelphia, Pa 19912 USA
We extend the investigations of the phase diagram of the Kondo Lattice, previously
performed by the groups of Coqblin, Burdin and Lacroix and their co-workers. In
particular, we investigate the stability of a variety of magnetic phases (commensurate
and incommensurate) as a function of the conduction electron concentration nc, the
exchange interaction J. The investigation has been extended to include the spin
degeneracy. The phase diagram shows a Kondo phase for large negative J and a series
of magnetic phases for smaller J, in agreement with the previous investigations and
also with the argument due to Doniach. For small values of the concentration of
conduction electrons, the Kondo temperature is exponentially depressed, in accord
with Nozieres ideas of Kondo Exhaustion. For small nc, the magnetic phases are
stabilized up to values of the exchange interaction which are comparable to the band
width. As nc is varied, the character of the small J magnetic phases, change from
ferromagnetic at low nc through a series of incommensurate spin-density wave phases
and to a Neel state at half-filling.
97
Th-S20-3
Mengminwei R139
Steady state dynamics in a model system of strongly correlated
electrons: effective temperatures near local quantum criticality
Farzaneh Zamani1∗, Pedro Ribeiro2 and Stefan Kirchner3
1. Max Planck Institute for Physics of Complex Systems, 01187 Dresden, Germany
2. CeFEMA, Instituto Superior Tcnico, Universidade de Lisboa, Av. Rovisco Pais,
1049-001 Lisboa, Portugal
3. Center for Correlated Matter and Department of Physics, Zhejiang University,
Hangzhou, 310027, China
(Dated: January 14, 2016)
Strongly correlated systems far from equilibrium have recently generated
considerable interest. This interest has mainly been spurred by experimental progress
in preparing and characterizing such systems out of equilibrum. The theoretical
understanding on the other hand suffers from a lack of methods that can reliably treat
strongly orrelated systems in and out of equilibrium at an equal footing. Here, we
present our results for the thermal and non-thermal steady-state scaling functions and
steady-state dynamics in a model of local quantum criticality. Such a quantum critical
state, where Kondo screening is destroyed in a critical fashion, is realized in a number
of rare earth intermetallics. This raises the possibility of experimentally testing for the
existence of fluctuation-dissipation relations far from equilibrium in terms of effective
temperatures. Our model, the pseudogap Kondo model, allows us to obtain full
scaling functions in and out of equilibrium. We also study the concept of effective
temperatures for correlations far from equilibrium near fully interacting as well as
weak coupling fixed points. In the vicinity of each fixed point we establish the
existence of an effective temperature different at each fixed point such that the
equilibrium fluctuation-dissipation theorem is recovered. Most interestingly,
steady-state scaling functions in terms of the effective temperatures coincide with the
equilibrium scaling functions in terms of the equilibrium temperature. That this result
extends to higher correlation functions will be explicitly demonstrated. Finally, we
compare our results to those expected for a conventional spin-density type quantum
critical point.
References:
P. Ribeiro, F. Zamani, S. Kirchner, Phys. Rev. Lett. 115, 220602 (2015).
F. Zamani, P. Ribeiro, S. Kirchner, in preparation.
∗ [email protected]
98
Th-S20-4
Mengminwei R139
Excitonic phases in correlated electron systems and Ta2NiSe5
Y. Ohta1, T. Kaneko1, K. Sugimoto2, K. Hamada1, H. Nishida1
1.
2.
Department of Physics, Chiba University, Chiba 263-8522, Japan
Center for Frontier Science, Chiba University, Chiba 263-8522, Japan
The electron-hole pair (or exciton) condensation in strongly correlated electron
systems (SCES) has attracted much attention because a number of new candidate
materials in this class have been discovered in recent years. Excitonic insulator states,
which were explored half a century ago in weakly correlated semiconductors and
semimetals, thus need to be revisited. In the SCES, the spin and lattice degrees of
freedom as well as the orbital ones play essential roles, so that we have to use
tight-binding lattice models rather than free-electron gas models. In this paper, we
therefore consider the excitonic phases in the SCES on the basis of the two-band
Hubbard model, where we take into account the intra- and inter-orbital Coulomb and
exchange interactions, as well as the phonon degrees of freedom. We thereby discuss
the excitonic charge and spin density-wave states derived respectively by the
spin-singlet and spin-triplet excitonic condensations and clarify the difference
between the excitonic and conventional density waves, putting particular emphasis on
their experimental consequences such as the bond order and magnetic multipole
formations. See Refs.[1]-[8] for details. We also discuss the electronic state and
observed phase transition of Ta2NiSe5, a promising candidate material for the
spin-singlet excitonic condensation [2,8].
Reference:
[1] T. Kaneko, K. Seki, and Y. Ohta, PRB 85, 165135 (2012)
[2] T. Kaneko, T. Toriyama, T. Konishi, and Y. Ohta, PRB 87, 035121 (2013)
[3] T. Kaneko, S. Ejima, H. Fehske, and Y. Ohta, PRB 88, 035312 (2013)
[4] S. Ejima, T. Kaneko, Y. Ohta, and H. Fehske, PRL 112, 026401 (2014)
[5] K. Seki et al., PRB 90, 155116 (2014)
[6] T. Kaneko and Y. Ohta, PRB 90, 245144 (2014)
[7] T. Kaneko, B. Zenker, H. Fehske, and Y. Ohta, PRB 92, 115106 (2015)
[8] K. Sugimoto, T. Kaneko, and Y. Ohta, PRB 93, 041105(R) (2016)
99
Th-S20-5
Mengminwei R139
Quantum Orders and Excitations in Kagome-Lattice Magnets
A. L. Chernyshev1 and M. E. Zhitomirsky2
1.
2.
Department of Physics and Astronomy, University of California, Irvine, California, USA
Service de Physique Statistique, Magnetisme et Supraconductivite, CEA-INAC/UJF,
Grenoble, France
Our recent works have advanced theoretical understanding of the quantum effects
in kagome-lattice antiferromagnets and have provided insights into the quantum
order-by-disorder mechanism, important for a broad class of frustrated spin systems.
In particular, we have challenged a general expectation that the quantum and thermal
order-by-disorder mechanisms always select the same ground state. We have shown
that the non-linear terms in the quantum hamiltonian of the anisotropic kagome-lattice
antiferromagnets can yield a rare example of the ground state that is different from the
one favored by thermal fluctuations. We have also demonstrated that the order
selection is generated by topologically non-trivial tunneling processes, yielding a new
energy scale in the system.
Related to the ground-state selection mechanism are the non-linear effects in the
spectra of the kagome-lattice systems. Further progress has been made in
understanding spectral properties of realistic kagome-lattice antiferromagnets such as
Fe-jarosite, for which we have demonstrated a remarkable wipe-out effect for a
significant portion of the spectrum. This phenomenon is related to an existence of the
so-called "flat mode," a ubiquitous feature of the kagome-lattice and other
highly-frustrated antiferromagnets, and is due to a resonant-like decay processes
involving two of such modes.
References:
[1] A. L. Chernyshev and M. E. Zhitomirsky, Phys. Rev. Lett. 113, 237202 (2014).
[2] A. L. Chernyshev, Phys. Rev. B 92, 094409 (2015).
[3] A. L. Chernyshev and M. E. Zhitomirsky, Phys. Rev. B 92, 144415 (2015).
(Editors' Suggestion).
100
Th-S20-6
Mengminwei R139
Crystallization of Magnetic Vortex Strings in Frustrated Magnets
Z. Wang1, Y. Kamiya2, A. H. Nevidomskyy1, C. D. Batista3
2. iTHES Research Group and Condensed Matter Theory Laboratory, RIKEN,
Saitama, Japan
3. Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico,
USA
One of the most striking consequences of strong electron correlations is the
emergence of new exotic quantum phases. Of particular interest are such emergent
quantum phases in frustrated spin systems, which result in complex magnetic states.
Here, I will present an exact result for a frustrated spin-1/2 model on cubic FCC and
BCC lattices in an applied magnetic field. Because of the cubic symmetry, the
spin-wave spectrum in high magnetic fields has multiple degenerate minima at
non-coplanar wavevectors. At the saturation field, a quantum phase transition occurs
and the spectrum becomes gapless, characterized by the boson condensate. Solving
the problem exactly in the dilute boson limit just below the saturation field, we find
several emergent vortex crystal phases, in which vortices form a three-dimensional
network (rather than a two-dimensional lattice as in type-II superconductors). Very
recently, a similar three-dimensional crystal of vortices/skyrmions has been found
experimentally in the cubic B20 material MnGe [2].
References:
[1] Z. Wang et al., Phys. Rev. Lett. 115, 107201 (2015).
[2] T. Tanigaki et al., Nano Letters, 15, 5438–5442 (2015)
101
Fr-S21-1
Mengminwei R225
Friday 8:30-9:00
New Broken Time-reversal Symmetry Superconductors: Theoretical
Constraints on Pairing States and Mechanisms
Jorge Quintanilla
Hubbard Theory Consortium, University of Kent, Canterbury, Kent, CT2 7NH, United Kingdom
In BCS theory superconductivity and magnetism are antagonistic. This makes
superconducting instabilities that break time-reversal symmetry rare and striking.
Group theory can be used to place constraints on the pairing state. I will review the
present situation, paying particular attention to materials such as LaNiC2, LaNiGa2,
Re6Zr and R5Rh6Sn18 where broken TRS has been observed in recent years. I will
discuss what group theory tells us about their pairing symmetries and its implications
for the quasiparticle spectra and pairing mechanisms, emphasizing some marked
differences with earlier paradigmatic examples including URhGe2, UGe2, Sr2RuO4
and UPt3.
102
Fr-S21-2
Mengminwei R225
Friday 9:00-9:30
Chiral d-wave superconductivity in SrPtAs
M. H. Fischer1, T. Neupert2, C. Platt3, A. P. Schnyder4, W. Hanke5, J. Goryo6, R.
Thomale5, M.Sigrist7,
1. Weizmann Institute of Science, Israel
2. Princeton University, USA
3. Stanford University, USA
4. Max-Planck-Institut fuer Festkoerperforschung, Germany
5. University of Wuerzburg, Germany
6. Hirosaki University, Japan
7. ETH Zurich, Switzerland
Recent muSR measurements on SrPtAs revealed time-reversal-symmetry breaking
with the onset of superconductivity, suggesting an unconventional superconducting
state. We have investigated this possibility via functional renormalization group and
find a chiral (d+id)-wave order parameter favored by the multiband fermiology and
hexagonal symmetry of SrPtAs. This (d+id)-wave state exhibits significant gap
anisotropies as well as gap differences on the different bands, but only has point
nodes on one of the bands at the Brillouin zone corners. The topological
characteristics of this superconducting phase include Majorana-Weyl nodes in the
bulk, protected surface states, and an associated thermal Hall response. The lack of
extended nodes and the spontaneously broken time-reversal symmetry of the
(d+id)-wave state are in agreement with the muSR experiments. Our theoretical
findings together with the experimental evidence thus suggests that SrPtAs is the first
example of chiral d-wave pairing and a Weyl superconductor.
103
Fr-S21-3
Mengminwei R225
Friday 9:30-9:45
Effect of Orbital Nematicity on Superconductivity in the Iron
Pnictides and Chalcogenides
Rong Yu1, Andriy H. Nevidomskyy2
1. Departmentof Physics, Renmin University of China, Beijing, China
Orbital ordering leading to the observed nematic phase in the iron-based
superconductors has been firmly established in a variety of experiments. It is therefore
important to investigate the effect of the orbital order on the superconductivity. To
this end, we have performed strong-coupling calculation within the slave-boson
approach to the multiorbital t-J1-J2 models for the iron-based superconductors. We
report the phase diagram as a function of both electron/hole doping and the orbital
ordering strength. We find that the amplitude of the otherwise dominant A1g (s±)
pairing channel diminishes as the strength of orbital ordering is increased, yielding to
the B1g (dx2-y2) pairing channel. This effect is especially pronounced in the
electron-doped case, with the d-wave pairing stabilized by the realistic values of the
orbital splitting ~50 meV. While the d-wave pairing has not been conclusively
observed in the iron-based superconductors, the competition between the s- and
d-wave pairing found in the calculations may have ramifications for FeSe, KFe2As2
and KxFe2-ySe2.
104
Fr-S21-4
Mengminwei R225
Friday 9:45-10:00
Identifying detrimental effects for multi-band superconductivity –
Application to Sr2RuO4
Aline Ramires1 and Manfred Sigrist2
1. Institute for Theoretical Studies, ETH Zurich, 8092 Zurich, Switzerland
2. Institute for Theoretical Physics, ETH Zurich, 8093 Zurich, Switzerland
Spin polarization and anti-symmetric spin-orbit coupling are detrimental to Cooper
pairing in the spin singlet and spin triplet channel, respectively. These are the
well-known features of paramagnetic limiting and selection rules in
non-centrosymmetric superconductors. We propose a general scheme to probe the
compatibility of arbitrary pairing states with given normal state properties in model
systems. This yields a universal criterion which we validate with results based on
weak coupling analysis of the stability of different superconducting gaps under
time-reversal and inversion symmetry breaking fields. Our criterion does, however,
not address directly any aspects concerned with the pairing mechanism.
A merit of the criterion is that it can be easily applied to the stability analysis of
superconducting states in multi-band systems, to establish gap structures favourable
within a given complex band structure. As such it can serve as a tool to identify
non-trivial mechanisms to suppress superconductivity under various external
influences, in particular, magnetic fields or distortions. We apply our criterion to the
multi-band superconductor Sr2RuO4 with the aim to explore possible explanations for
the limiting feature observed in the in-plane upper critical field.
*This work was supported by Dr. Max Rossler, the Walter Haefner Foundation and the
ETH Zurich Foundation (AR) and by the Swiss National Science Foundation (MS).
105
Fr-S22-1
Mengminwei R139
Friday 8:30-9:00
Skyrmions with ferroelectric polarization in multiferroic GaV4S8
E. Ruff1, Zhe Wang1, P. Lunkenheimer1, H.-A. Krug von Nidda1, D. Ehlers1, V.
Tsurkan1,2, S. Bordács3, I. Kézsmárki1,3, D. Grundler4, A. Loidl1
1. Experimental Physics V, Center for Electronic Correlations and Magnetism,
University of Augsburg, 86135 Augsburg, Germany
2. Institute of Applied Physics, Academy of Sciences of Moldova, Chisinau
MD-2028, Republic of Moldova
3. Department of Physics, Budapest University of Technology and Economics
and MTA-BME Lendület Magneto-optical Spectroscopy Research Group,
1111 Budapest, Hungary
4. EPFL STI IMX LMGN, MXC 241, Station 12, 1015 Lausanne, Switzerland
The lacunar spinel GaV4S8 undergoes orbital ordering at 44 K and reveals a
complex magnetic phase diagram below 13 K, including a ferromagnetic, cycloidal
and Néel-type skyrmion lattice phase. [1] Skyrmions are topologically protected
nano-scale spin vortices with fascinating physical properties and high potential for
future data storage. Based on magnetic susceptibility, heat capacity and pyrocurrent
measurements, all as function of temperature and magnetic field, we construct a
detailed phase diagram and in addition, we provide a thorough study of the polar
properties of GaV4S8, revealing that its orbitally ordered phase is ferroelectric with
sizable polarization of 1 μC/cm2. Moreover, spin-driven excess polarizations emerge
in all magnetic phases; hence, GaV4S8 hosts three different multiferroic phases
including the skyrmion lattice formed by ferroelectric spin vortices. [2] By taking into
account the crystal symmetry and spin patterns of the magnetically ordered phases,
exchange striction is identified as the main microscopic mechanism behind the
spin-driven ferroelectric polarization in all multiferroic phases. The polar crystal
structure of GaV4S8 is unique among the known skyrmion-lattice host materials and
the ferroelectric SkL phase may be exploited for non-dissipative electric-field control
of skyrmions.
In the second part of this talk we present detailed results using THz and broadband
microwave spectroscopy. We find an intriguing relaxation dynamics in the THz range
indicating the divergence of relaxation times coupled to the orbital dynamics and
establishing an orbitally driven ferroelectric phase. [3] In addition, using coplanar
waveguide absorption spectroscopy we study magnetic excitations of the skyrmion
lattice, the helical and induced ferromagnetic spin phases. [4]
Reference:
[1] I. Kézsmárki et al., Nature Materials 14, 1116 (2015)
[2] E. Ruff et al., Science Advances 1, E1500916 (2015)
[3] Zhe Wang et al., Phys. Rev. Lett. 115, 207601 (2015)
[4] D. Ehlers et al., (2015), unpublished, arXiv:1512.02391
106
Fr-S22-2
Mengminwei R139
Friday 9:00-9:30
Electrical Control of Large Magnetization Changes in Helimagnets
Kee Hoon Kim
Center for Novel States of Complex Materials Research, Department of Physics
and Astronomy, Seoul National University, Seoul 151-747, Korea
Despite its technical and fundamental importance, large variation of macroscopic
magnetization by an electric field (E) has rarely been achieved in bulk materials and
remains a considerable challenge. Here, we present recent progresses of the subject in
multiferroic ferrites with the hexagonal structure; room temperature modulation and
large reversal of magnetization (M) by E have been realized in the Co 2Z-type and
Zn2Y-type hexaferrites, respectively. In both systems, a transverse conical spin state
plays a major role in exhibiting remanent M and electric polarization. In the former,
the magnetization is modulated up to 0.34 μB per f.u. in an electric field of 1.14
MV/m with nonvolatile, magnetoelectric reading- and writing-operation capability
entirely at room temperature. In the latter, upon sweeping E through the range of ±2
MV m-1, M varied quasi-linearly in the range of ±2 μB per f.u., resulting in the
reversal of M. Moreover, the remanent M exhibited non-volatile changes of ±0.15 μB
per f.u., depending on the history of the applied electric fields. The strong modulation
and non-volatile two-states of M at zero magnetic field were observable up to ~150 K.
Based on the above progresses, we extract design principles for realizing the large
magnetization reversal at room temperature. We suggest that soft ferrimagnetism with
small magnetic anisotropy and the related transverse conical state with high ordering
temperature are key ingredients to achieve the giant converse magnetoelectric effect
at room temperature [1-4].
In close collaboration with Kwangwoo Shin, Changbae Park, Saehwan Chun,
Yisheng Chai, Sangil Kwon, Choonchil Lee, Jae Ho Chung, and Jae Hoon Park.
Reference:
[1] K. W. Shin et al., preprint;
[2] Y. S. Chai et al., Nature comm. 5, 4208 (2014);
[3] Sae Hwan Chun et al., Phys. Rev. Lett. 108, 177201 (2012); ibid, 104, 037204
(2010)
107
Fr-S22-3
Mengminwei R139
Friday 9:30-9:45
Driving Spin Excitations by Hydrostatic Pressure in BiFeO3
J. Buhot1,*, C. Toulouse1, Y. Gallais1, A. Sacuto1, R. de Sousa2, D. Wang3, L.
Bellaiche4, M.Bibes5, A. Barthélémy5, A. Forget6, D. Colson6, M. Cazayous1 and
M-A. Measson1.
1. Laboratoire Matériaux et Phénomènes Quantiques, UMR 7162 CNRS,
UniversitéParis Diderot, Bâtiment Condorcet 75205 Paris Cedex 13, France
2. Department of Physics and Astronomy, University of Victoria, Victoria,
British Columbia, Canada, V8W 2Y2
3. Electronic Materials Research Laboratory–Key Laboratory of the Ministry of
Education, and International Center for Dielectric Research, Xi’an Jiaotong
University, Xi’an 710049, China
4. Physics Department and Institute for Nanoscience and Engineering,
University of Arkansas, Fayetteville, Arkansas 72701, USA
5. UnitéMixte de Physique CNRS/Thales, 1 avenue Augustin Fresnel, Campus
de l’Ecole Polytechnique, F-91767 Palaiseau, France et UniversitéParis-Sud,
91405 Orsay, France
6. Service de Physique de l’Etat Condensé, CEA Saclay, IRAMIS, SPEC (CNRS
URA 2464),
F-91191 Gif sur Yvette, France
* Present address: High Field Magnet Laboratory, Institute for Molecules and
Materials, Radboud University Nijmegen, Toernooiveld 7, 6525 ED Nijmegen,
The Netherlands
The spin-lattice interaction plays a decisive role in mediating the combined ferroic
properties of multiferroic materials, including in the prototypical multiferroic
compound BiFeO3, an ideal candidate for spintronics, electro-optics and data storage
applications [1]. We elucidate here the coupling between spin excitations and
structure thanks to a new advanced high-pressure technique combined with analytical
and computational theory. Thanks to the development of a new Raman spectroscopy
set-up probing very low energy excitations (0.6 meV) under high pressure, for the
first time, we have been able to follow simultaneously the phonon modes and the
magnetic excitations in BiFeO3 bulk up to 12 GPa [2]. As pressure increases, multiple
spin excitations associated to non-collinear cycloidal magnetism collapse into two
excitations, which show jump discontinuities at some of the ensuing crystal phase
transitions. Using effective Hamiltonian simulations of both the structure and the
magnetism and Ginzburg-Landau theoretical calculations we demonstrate that the
structural phases and the magnetic anisotropy drive and control the spin excitations.
Reference:
[1] W. Eerenstein et al., NATURE 442, 759 (2006)
[2] J. Buhot et al., PHYSICAL REVIEW LETTERS 115, 267204 (2015)
108
Fr-S22-4
Mengminwei R139
Friday 9:45-10:00
Converting the Interfacial dipole field in Bi6(Fe,Co)Ti3O18
multiferroic thin films
Yu Yun1, Chao Ma1, Haoliang Huang1, Dechao Meng1, Jianlin Wang1, Zhengping Fu1,
Ranran Peng1, Gail J. Brown2, Yalin Lu1,3,4, Xiaofang Zhai1
1. Hefei National Laboratory for Physical Sciences at the Microscale and
Materials Science Department, University of Science and Technology of China,
Hefei 230026, Anhui, China,
2. Materials and Manufacturing Directorate, Air Force Research Laboratory,
Wright-Patterson Air Force Base, OH 45433-7707, USA
3. Laser Optics Research Center, Department of Physics, United States Air
Force Academy, CO80840, USA
4. National Synchrotron Radiation Laboratory, University of Science and
Technology of China, Hefei 230026, Anhui, China
Many multiferroic materials contain layers of non-compensated ionic charges
which generate a large electric dipole field.[1] One of the most prominent examples is
the recent discovered Aurivillius type room-temperature multiferroics, in which two
magnetic ions of Fe and Co are doped into the ferroelectric parent compound of
Bi4Ti3O12.[2] At the interface of the polar Bim+1(Fe,Co)m-3Ti3O3m+3 film and the
non-polar or weakly polar substrate, a subsequent large dipole field could in principle
manipulate the film property. We chose to balance the large dipole field in
Bi6FeCoTi3O18 by a conducting oxide LaNiO3 buffer layer or not balance it. And we
found large differences in the multiferroic films tipped by the delicate interface
electronic reconstruction.[3] This study carefully extended the knowledge we have
gained in the study of perovskite oxide interface[4-5] to the new field of layered oxide
interface.
Reference:
[1] N. Nakagawa, H. Y. Hwang, and D. A. Muller. Nat. Mater. 5, 204 (2006).
[2] Y. L. Lu, et.al. Appl. Phys. Lett. 95, 082901 (2009).
[3] X. Zhai, Y. L. Lu, et. al. Appl. Phys. Lett. 107, 011602 (2015).
[4] X. Zhai, Y. Liu, et.al. Nat. Commun. (2014).
[5] X. Zhai, J. N. Eckstein, et.al. Adv. Mater. (2010).
109
Fr-S23-1
Mengminwei R225
Friday 10:30-11:00
Exploration of superconductivity in the pressure-induced
helimagnetic quantum critical point
J.-G. Cheng1, W. Wu1, K. Matsubayashi2, J. P. Sun1, F. K. Lin1, J. L. Luo1, Y.
Uwatoko2
1. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics,
Chinese Academy of Sciences, Beijing 10090, China
2. Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
One of the common features of unconventional superconducting systems such as
the heavy fermion, high-Tc cuprate and iron-pnictide superconductors is that the
superconductivity emerges on the border of long-range magnetically ordered state. In
addition to doping charge carriers, the application of hydrostatic pressure provides an
effective and clean means for searching novel classes of unconventional
superconductors near the magnetic quantum critical point. By following this approach,
I will present our recent effort in exploring the possible unconventional
superconductivity near the helimagnetic quantum critical point of CrAs and MnP[1,2].
Reference:
[1] W. Wu, et al., Nat. Comm. 5, 5508 (2014)
[2] J.-G. Cheng, et al., PRL 114, 117001 (2015)
110
Fr-S23-2
Mengminwei R225
Friday 11:00-11:30
Pressure Study on Cd-doped Heavy Fermion Superconductor
CeIrIn5
Ye Chen1, W. B. Jiang1, C. Y. Guo1, F. Ronning2, E. Bauer2, Tuson Park3, H. Q.
Yuan1, Z. Fisk4, J. D. Thompson2, Xin Lu1
1
Center for Correlated Matter and department of Physics, Zhejiang University, Hangzhou, China
2
Los Alamos National Laboratory, Los Alamos, NM, USA
3
Department of Physics, Sungkyunkwan University, Suwon, South Korea
4
Long range antiferromagnetic (AFM) order emerges with a minor amount of Cd
doping in the heavy fermion superconductor CeIrIn5, while the AFM is discovered to
be gradually suppressed under pressure with re-emergent superconductivity through
electrical resistivity and ac calorimetry measurements. However, no signatures of
quantum criticality are observed at the presumed pressure and the pressure induced Tc
is close to that of the pristine CeIrIn5, which supports the local origin of the AFM
moments in Cd-CeIrIn5 where spin-droplets nucleate around Cd dopants due to
enhanced critical fluctuations.
Reference:
[1] Y. Chen et al., PRL 114, 146403 (2015)
111
Fr-S23-3
Mengminwei R225
Friday 11:30-11:45
Pressure-induced heavy fermion superconductivity deep inside the
magnetic phase of CeAu2Si2
D. Jaccard1, G. W. Scheerer1, Z. Ren1, G. Lapertot2,
1. DQMP-University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland
2. SPSMS, UMR-E CEA/UJF-Grenoble 1, INAC, Grenoble, F-38054, France
Electrical resistivity, thermopower and ac calorimetry measurements reveal that, at
a pressure p ~ 15 GPa, bulk unconventional superconductivity emerges in CeAu2Si2
not at the verge of the magnetic phase as usually observed, but at a minimum of the
magnetic ordering temperature TM where quantum criticality also occurs. The
superconducting temperature onset Tc coincides with the temperature T* of a
magnetic rearrangement and, over a broad p range, both quantities, as well as TM
increase by a factor of about two, almost up to pc ~ 22 GPa where TM abruptly
vanishes and Tc reaches a maximum of 2.5 K. On the high-p side of the huge
superconducting domain (12–27 GPa) there is evidence of valence or orbital
fluctuations, which may play a role in the pairing mechanism. While resistivity
indicates a rapid p-increase of the Kondo coupling, a negative thermopower peak is
observed up to pc at a weakly p-dependent temperature (30–50 K), and is interpreted
as a precursor to superconductivity. Comparisons with similar compounds including
CeCu2Si2 and CeCu2Ge2 are made.
References:
[1] Z. Ren et al., PRX 4, 031005 (2014) and Phys. Rev. B 91, 094515 (2015)
112
Fr-S23-4
Mengminwei R225
Friday 11:45-12:00
Superconductivity and Pressure-induced Quantum Criticality in the
Antiferromagnetic Heavy Fermion Compound Ce3PtIn11
J. Prokleška1, M. Kratochvílová1, K. Uhlířová1, V. Sechovský1, J. Custers1
1. Charles University in Prague, Faculty of Mathematics and Physics, Ke Karlovu 5,121 16
Prague 2, Czech Republic
We report on resistivity, magnetization and specific heat experiments conducted at
ambient and under hydrostatic pressure on the recently discovered multi–site cerium
heavy fermion compound, Ce3PtIn11 [1,2]. The material belongs to the CenTmIn3n+2m
class of layered materials which comprises a numerous amount of compounds
including CeCoIn5, CeRhIn5 and Ce2RhIn8. The compound is structurally equal to
Ce3PdIn11 (tetragonal, space group P4/mmm) replacing Pd by Pt [3]. The lattice
constants are a = 4.6874(4) Å and c = 16.8422(12) Å. There are two non-equivalent
Ce-sites. Ce2 resides the Wyckoff 1a place which has local C4v symmetry. The ion is
experiences CeIn3 environment. The Ce1-site occupies the 2g position (D4h
symmetry). Its surrounding is identical to Ce-atoms in Ce2PtIn8 [1]. At ambient
condition the material shows remarkable properties: in the absence of magnetic field,
Ce3PtIn11 undergoes two successive magnetic transitions at T1 = 2.2 K and TN = 2.0 K,
respectively, and becomes superconducting (SC) below Tc = 0.35 K [2].
Upon applying hydrostatic pressure (p) T1 and TN reduce and intersect with the SC
state at p ≈ 1.1GPa. Extrapolation of TN → 0 reveals a critical pressure of pc =
1.3GPa, i.e., the quantum critical point (QCP). For 1.1 < p < 1.6 GPa,
superconductivity evolves out of a non-fermi liquid state which is characterized by an
almost T -linear resistivity from Tc ( ≈ 0.7 K) to temperatures even higher than T >
5K. The maximum in Tc is located at ≈ 1.3 GPa and hence strongly suggests critical
fluctuations associated with the magnetic QCP are responsible for Cooper-pairing.
Reference:
[1] M. Kratochvílováet al., J. Cryst. Growth 397, 47 (2014).
[2] J. Prokleška et al., Phys. Rev. B 92, 161114(R) (2015).
[3] M. Kratochvílováet al., Sci. Rep. 5, 15904 (2015).
113
Fr-S23-5
Mengminwei R225
Friday 12:00-12:15
Strong Coupling Superconductivity and Structural Quantum
Criticality in (Ca,Sr)3Rh4Sn13
W. C. Yu1, Y. W. Cheung1, P. J. Saines2, M. Imai3, T. Matsumoto3, C. Michioka3, K.
Yoshimura3, and Swee K. Goh1
1. Department of Physics, The Chinese University of Hong Kong, Hong Kong, China
2. Department of Chemistry, University of Oxford, Oxford, United Kingdom
3. Department of Chemistry, Kyoto University, Kyoto, Japan
The concept of structural quantum criticality was recently advanced to understand
the temperature–x (x=pressure or chemical composition) phase diagrams of
(Ca,Sr)3Ir4Sn13 [1] and (Ca,Sr)3Rh4Sn13 [2]. In both systems, a second-order structural
transition temperature T* can be completely suppressed to 0 K by varying x, and a
dome-shaped variation of the superconducting transition temperature is found in the
vicinity of the structural quantum critical point where T*→0 K. Using heat capacity,
we further establish that superconductivity in (Ca,Sr)3Rh4Sn13 evolves into the strong
coupling regime on approaching the structural quantum critical point [3]. The relevant
normal state and superconducting state parameters will be presented and the evolution
of the coupling strength will be discussed in the framework of structural quantum
criticality.
References:
[1] L. E. Klintberg et al., Phys. Rev. Lett. 109, 237008 (2012)
[2] S. K. Goh et al., Phys. Rev. Lett. 114, 097002 (2015)
[3] W. C. Yu et al., Phys. Rev. Lett. 115, 207003 (2015)
114
Fr-S24-1
Mengminwei R139
Friday 10:30-11:00
Coherence and Crystal Fields in Ce-based heavy Fermions
Z. Fisk1
1. Department of Astronomy and Physics, University of California Irvine, Irvine CA
The establishment of coherent Bloch states in heavy Fermion materials involves
entangling the f-spin degrees of freedom with those of the conduction electrons with
corresponding change in the Fermi surface. Coherence only develops when excited
crystal field levels become depopulated in heavy Fermions, intermediate valent
materials belonging to a different regime of f-electron – conduction electron coupling.
Kondo insulators are argued to be a particular instance of coherent behavior, with data
from La3Bi4Pt3 – Ce3Bi4Pt3 alloys showing how coherence develops only at high Ce
concentration.
115
Fr-S24-2
Mengminwei R139
Friday 11:00-11:30
Divalent, Trivalent, Intermediate, and Heavy Fermion Properties in
Eu Compounds
Yoshichika Ōnuki1, Ai Nakamura2, Fuminori Honda2, Tetsuya Takeuchi3, Miho
Nakashima4,Yasushi Amako4, Hisatom Harima5, Kazuyuki Matsubayashi6, Yoshiya
Uwatoko6, Shuei Kayama7,Tomoko Kagayama7, Katsuya Shimizu7, Hiromu Akamine8,
Keisuke Tomori8, Yosuke Ashitomi8,Tomoyuki Yara8, Masato Hedo1, and Takao
Nakama1
1. Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan
2. Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan
3. Low Temperature Center, Osaka University, Toyonaka, Osaka 560-0043, Japan
4. Faculty of Science, Shinshu University, Matsumoto, Nagano 390-8621, Japan
5. Graduate School of Science, Kobe University, Kobe 657-8501, Japan
6. Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
7. Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan
8. Graduate School of Engineering and Science, University of the Ryukyus, Nishihara,
Okinawa 903-0213, Japan
Most of the Eu compounds are in the divalent (Eu2+) electronic state, and order
magnetically. An energy difference between the Eu2+ and Eu3+ states is, however, not
so large. Therefore, the valence transition occurs in some Eu compounds from the
divalent state at high temperatures to a nearly trivalent state at low temperatures, as in
EuPd2Si2. The valence transition is also accelerated by applying pressure, as in
EuRh2Si2. We present the characteristic electronic properties of the Eu compounds
from the following four viewpoints: (1) A simple canting magnetization was observed
in antiferromagnets of EuBi3, EuCd11, EuGa4, and EuPb3. We propose a relation
between the saturation field Hc and TN-θp, namely Hc = (kB/3μB)(TN-θp), based on an
antiferromagnetic two-sublattice model. Fermi surfaces of these Eu-divalent
compounds are well explained by the results of energy band calculations for the
corresponding non-4f reference Sr compounds. (2) The trivalent Eu compounds are
present but are small in number. The typical compound is EuPd3. The Fermi surface
properties of EuPd3 are well explained from the results of energy band calculations in
the LDA+U- scheme. This means that the 4f orbitals are far separated from the Fermi
level, and do not contribute to the conduction electrons. (3) EuNi2P2 is known as a
heavy fermion compound with γ = 93 mJ/(K2·mol). This heavy fermion state is based
on the Kondo effect, as in CeRu2Si2, revealing an intensive shrinkage of the volume
below about 100 K in the temperature dependence of thermal expansion. Namely, the
thermal expansion coefficient has a peak at 40 K. The Kondo temperature is thus
determined as TK = 80 K. (4) By applying pressure for the divalent Eu compounds,
the electronic states are changed by the following two processes. One is due to the
valence transition at P = Pv, as in EuRh2Si2, mentioned above. Another corresponds to
the case of Eu2Ni3Ge5 and EuRhSi3 which are approaching to the quantum critical
point with increasing pressure, as in the cerium compounds.
116
Fr-S24-3
Mengminwei R139
Friday 11:30-11:45
An Orbitally Selective Kondo Effect in SrFe2-xNixAs2
N. Wakeham1, Ni Ni1, J.-X. Zhu1, E.D. Bauer1, J.D. Thompson1, F. Ronning1
1. Los Alamos National Laboratory, Los Alamos, NM, USA
Though one can describe many aspects of the iron-based superconductors within an
itinerant electron approach, there is also substantial evidence that a local moment
description must be included as well. Given the strong similarities between the P-T
phase diagrams of AFe2As2 (A=Ba, Sr, Ca) and Ce-based heavy fermion such as
CeMIn5 (M=Co, Rh, Ir), we were motivated to understand the response of the system
if we could examine an individual Fe atom in a non-magnetic analog. For dilute Fe
concentrations (< 1%) in paramagnetic SrNi2As2 we observe the single ion Kondo
effect in transport and thermodynamic measurements, with S=1/2 and TK ~ 5 K.
Increasing the iron concentration leads to a breakdown of the single ion scaling and a
dramatic increase in the characteristic energy scale in the system. A similar
renormalization of the Kondo scale is observed in the LaMIn5 systems with increasing
Ce concentration. We will discuss the surprising presence of the Kondo effect in the
Fe-based superconductors, their similarities with heavy fermion materials, and
whether it is appropriate to separate the spin and charge degrees of freedom.
117
Fr-S24-4
Mengminwei R139
Friday 11:45-12:00
Dilution and Doping Effects on the Antiferromagnetic Kondo
Semiconductor CeOs2Al10
T. Takabatake1,2, Y. Okada1, J. Kawabata1, Y. Yamada1, K. Hayashi1, T. Ekino3, Y.
Muro4,
1. Graduate School of Advanced Sciences of Matter
2. Inst. for Advanced Materials Research
3. Graduate School of Integrated Arts and Sciences, Hiroshima Univ.,
Higashi-Hiroshima, Japan
4. Faculty of Engineering, Toyama Prefectural University, Izumi, Japan
In so-called Kondo semiconductors with renormalized gaps at the Fermi level, the
ground states remain nonmagnetic due to the strong hybridization of the 4f states and
conduction bands. However, a recently found Kondo semiconductor CeOs 2Al10 orders
antiferromagnetically (AFM) at rather high temperature 28.5 K [1]. In order to
elucidate the mechanism of the AFM order, we have studied the effects of dilution
and electron- and hole-doping on the magnetic and transport properties [2,3] as well
as electron tunneling properties [4]. The AFM order is found to be robust against La
substitution for Ce while it is fragile against the 5d hole doping by Re substitution for
Os. Furthermore, 5d electron doping by Ir substitution for Os and 3p electron doping
by Si substitution for Al equally suppress the AFM order while the ordered moments
are increased from 0.3 to 1.0 B/Ce by the substitutions [5]. These findings reveal
that the AFM interaction is strongly weakened by any change in the density of 5d-3p
conduction electrons but is hardly affected by the violation of the coherent Ce
sublattice.
Reference:
[1] Y. Muro et al., PRB 81, 214401, 2010.
[2] J. Kawabata et al., PRB 89, 094404, 2014.
[3] Y. Muro et al., JPS Conf. Proc. 3, 012017, 2014.
[4] J. Kawabata et al., PRB 92, 201113(R), 2015.
[5] A. Bhattacharyya et al., PRB 90, 174422, 2014.
118
Fr-S24-5
Mengminwei R139
Friday 12:00-12:15
Emergent Kondo lattice behavior in iron-based superconductors
AFe2As2 (A = K, Rb, Cs)
Y. P. Wu1, D. Zhao1, A. F. Wang1, N. Z. Wang1, Z. J. Xiang1, X. G. Luo1,2,4, T. Wu1,2,4
and X. H.Chen1,2,3,4
1. Hefei National Laboratory for Physical Sciences at Microscale and Department of
Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
2. Key Laboratory of Strongly-coupled Quantum Matter Physics, Chinese Academy of
Sciences, School of Physical Sciences, University of Science and Technology of China,
Hefei, Anhui 230026,China
3. High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei, Anhui 230031,
China
4. Collaborative Innovation Center of Advanced Microstructures, Nanjing University,
Nanjing 210093, China
Here, we experimentally study the origin of d-electron heavy fermion (HF)
behaviour in iron-based superconductors (FeSCs) AFe2As2 (A = K, Rb, Cs) by
nuclear magnetic resonance on 75As. Our result reveals a universal
coherent-incoherent crossover with a characteristic temperature T*. Below T*, a
so-called "Knight shift anomaly" is first observed in FeSCs, which exhibits a scaling
behavior similar to f-electron HF materials. Furthermore, the scaling rule also
regulates the manifestation of magnetic fluctuation. These results undoubtedly support
an emergent Kondo lattice scenario for the d-electron HF behavior, which support the
AFe2As2 (A = K, Rb, Cs) as a material realization of d-electron HF superconductors.
Reference:
[1] Y. P. Wu et al., arXiv:1507.08732 (2015)
119
Poster Sessions
(Venue: Stadium)
120
Mo-P001
Stadium
Mo 13:30-15:30
Temperature-dependent Fermi Surface evolution and banddependent hybridization of CeCoIn5 studied by angle-resolved
photoemission spectroscopy
Q.Y. Chen1,2, R. Peng1, H.C. Xu1, D.F. Xu1, X.H. Niu1, H. Q. Yuan3, S. Kirchner3, L. Shu1, V.N.
Strocov4, P. Dudin5, M. Hoesch5, D.L. Feng1
1
State Key Laboratory of Surface Physics, Department of Physics, Fudan University, Shanghai,
China
2
Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang, China
3
Department of Physics, Zhejiang University, Hangzhou, China
4
Swiss Light Source, Paul Scherrer Institute, CH-5232 Villligen PSI, Switzerland
5
Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE, United
Kingdom
We report the three dimensional electronic structure of CeCoIn5 by bulk-sensitive
soft x-ray angle-resolved photoemission spectroscopy. Ce 4d-4f resonant (121 eV)
photoemission spectroscopy was also carried out to study the 4f electronic
characteristics. Moreover, temperature-dependent measurements have been performed
from below 10 K to 190 K, and demonstrate that the f electron is dominated by localized
character at high temperature and it starts to hybridize with the conduction electrons at
around 150 K. The hybridization is enhanced at lower temperature and shows banddependent. Enlargement of the electron-like pocket around the Brillouin zone corner
can be observed when f electron participates in the Fermi surface construction.
Meanwhile, large f-derived spectral weight can be clearly observed around the BZ
center. Our results demonstrate that the evolution from a large FS to a small FS does
exist upon increasing temperature, which is in agreement with the widely believed
predictions from theoretical aspects. However, the transition temperature is much
higher than TK, which may need further advance in theoretical approaches based on
Anderson model in order to elucidate the temperature dependence of Fermi surfaces in
this system.
Reference:
[1] F. Steglich et al., PRL 43, 1892 (1979)
[2] K. Kummeret al., PRX 5, 011028 (2015)
[3] P. Gegenwart, Q. Si, et al., Nat. Phys. 4, 186 (2008).
121
Mo-P002
Stadium
Mo 13:30-15:30
Pressure Evolution of Superconducting Critical Current Density
In CeRh(SnxIn1-x)5
Soon-Gil Jung1, Soonbeom Seo1, Sangyun Lee1, E. D. Bauer2, Tuson Park1,*
1
Department of Physics, Sungkyunkwan University, Suwon, SouthKorea
2
Los Alamos National Laboratory, Los Alamos, NM 87545, USA
We have investigated the pressure evolution of superconducting critical current (Ic)
for the heavy fermion superconductor CeRh(SnxIn1 -x)5 by performing current-voltage
(I-V) characteristic measurements. When subjected to 4.4% Sn doping, the quantum
critical point (QCP ~ 2.3 GPa) of CeRhIn5 is shifted to ~1.3 GPa and of the pressureinduced superconductivity emanates from the tuned QCP, showing adome like shape
[1]. The temperature dependence of Ic of CeRhSn0.22In4.78 at self-field and 1 Tesla
shows a similar dome-shape behavior, while the magnetic field dependence of Ic at
fixed temperatures shows an asymmetric dome. Even though the zero-field Ic(0) at
pressures above the QCP is slightly higher than that below the QCP, the field
dependence of Ic above the QCP decreases more rapidly than Ic(H) below the QCP,
implying that vortex pinning strength becomes weaker at pressures above the QCP. The
temperature dependence of Ic shows that spatial variations of superconducting transition
temperature (δTc-pinning) play a major role for Ic(T, H) at all pressures and the scaling
of flux pinning force density (FP) indicates that the main pinning source in the
CeRhSn0.22In4.78 is a point defect. In this presentation, we discuss the pressure evolution
of critical current (Ic) for CeRhSn0.22In4.78 and emphasize its relationship with the
pressure evolution of antiferromagnetism (AFM) and superconductivity near the
quantum critical point.
Reference:
[1] S. Seo, E. Park, E.D. Bauer, F. Ronning, J.N. Kim, J.-H.Shim, J.D. Thompson,
and Tuson Park, "Controlling superconductivity by tunable quantum critical points",
Nat. Commun.6, 6433 (2015).
122
Mo-P003
Stadium
Mo 13:30-15:30
Hg-doping effects on the quantum critical compound CeRhIn5
Soonbeom Seo1, Sol Ju1, E.D. Bauer2, J.D. Thompson2, Tuson Park1
1
Department of Physics, Sungkyunkwan University, Suwon 440-746, South Korea
2
Los Alamos National Laboratory, Los Alamos 87545, USA
CeRhIn5 is a prototypical antiferromagnet where the AFM ordering temperature (TN)
is suppressed with pressure to reveal an AFM quantum critical point at the optimal
pressure of 2.3 GPa [1, 2]. When doped with Hg, CeRh(In1-xHgx)5, TN initially decreases
with x, reaches a minimum and starts to increase for x > 0.0175 [3]. In this presentation,
we report electrical resistivity of the 0.45% and 1% Hg-doped CeRhIn5 under pressure.
The Hg doping locally changes the electronic states surrounding the Hg dopant, which
is similar to the inhomogeneous superconducting phases that were recently observed in
the Cd-doped CeCoIn5 [4]. Electrical resistivity of the 3.5% Hg-doped CeRhIn5, where
TN is similar to the pure CeRhIn5, will be additionally discussed.
Reference:
[1] T. Park et al., Nature, 440, 65 (2006).
[2] G. Knebel et al., Phys. Rev. B,74, 020501 (2006).
[3] E. D. Bauer et al., Physica B,403, 1135 (2008).
[4] S. Seo et al., Nature Physics, 10, 120 (2014).
123
Mo-P004
Stadium
Mo 13:30-15:30
Physical properties of CeIr(In1-xCdx)5 under pressure
R. Tsunoda1, Y. Hirose2, R. Settai2
1Graduate School of Science and Technology, Niigata University
2Department of Physics, Niigata University
CeIrIn5 is the heavy fermion superconductor with the electronic specific coefficient
γ of 700 mJ/K2･mol and the superconducting transition temperature Tc of 0.4 K at
ambient pressure[1]. Pressure dependence of Tc in CeIrIn5 indicates a maximum value
of ~ 1 K at P = 2.8 GPa[2]. This pressure is far from magnetic quantum critical point
[3,4]. Nuclear-quadrupole-resonance (NQR) measurement revealed that maximum Tc
of CeIr(In0.95Cd0.05)5 is higher than that of of CeIrIn5 by 30 %[5], suggesting that Cd
dope enhances magnetic fluctuation to the original superconductivity in CeIrIn5[4,5].
In order to understand the mechanism of superconductivity in CeIrIn5, we measured
electrical resistivity and AC specific heat of CeIr(In0.95Cd0.05)5 under pressure. We
observed an enhancement of Tc of 1.4K that is different from previous study[6],and
unconventional behavior that cannot be understood in the basis on the magnetic
fluctuation theory and valence one is observed.
Reference:
[1] H. Shishidoet al., J. Phys. Soc. Jpn. 71, 162 (2002).
[2] T. Muramatsuet al., Physica C 388-389, 539 (2003).
[3] S. Kawasaki et al., Phys. Rev. Lett. 94, 037007 (2005).
[4] M. Yashimaet al., Phys.Rev. Lett. 109, 117001 (2012).
[5] K. Tani, master thesis Osaka Univ. (2014).
[6] Y. Chen et al., Phys.Rev. Lett. 114, 146403 (2015)
124
Mo-P005
Stadium
Mo 13:30-15:30
Enhancement of Tc in CeIr(In1-xCdx)5 studied by In-NQR
M. Yashima1 , K. Tani1, K. Nishimoto1, H. Mukuda1, Y. Kitaoka1, F. Honda2, R. Settai3, and Y.
Onuki4
1
Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531,
Japan
2
Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan
3
Department of Physics, Niigata Univ., Ikarashi, Niigata, 950-2181, Japan
4
Department of Physics and Earth Sciences, Faculty of Science, University of the
Ryukyus, Nishihara, Okinawa 903-0213, Japan
We report on superconducting characters under pressure in CeIr(In1−xCdx)5 by
meansof In-Nuclear-Quadrupole-Resonance (NQR) studies. In CeIr(In0.925Cd0.075)5, the
superconductivity is suppressed and the inhomogeneous antiferromagnetic order at TN~
2.3 K is induced by Cd dopants at ambient pressure. However, the measurements of a
nuclear-spin-lattice-relaxation rate 1/T1 have revealed that the superconductivity
suddenly occurs above 2.1 GPa [1]. Furthermore, we confirmed that Tc under pressure
in CeIr(In0.95Cd0.05) 5 is higher than the maximum Tc(~ 0.9 K) in pure CeIrIn5. These
results suggest that the Cd-doping induces the strong coupling superconductivity inthe
CeIrIn5 system.
Reference:
[1] M. Yashima et al., Phys. Rev. Lett., 109, 117001 (2012).
125
Mo-P006
Stadium
Mo 13:30-15:30
Single energy scale model of metamagnetism in CeCoIn5
S. Ramakrishnan1, A. Thamizhavel1, B. D. White2, M. B. Maple2, Pradeep Kumar3, V. Celli4
and B. S. Shivaram4
1
Department of Condensed Matter Physics and Materials Science, Tata Institute of
Fundamental Research, Dr. HomiBhabha Road, Colaba, Mumbai 400005, India
2
Department of Physics and Center for Advanced Nanoscience, University of California, La
Jolla, San Diego, CA. 92093
3
4
Department of Physics, University of Florida, Gainesville, FL, USA
Department of Physics, University of Virginia, Charlottesville, Virginia 22901, USA
We report on the anisotropic linear and non-linear magnetic response of the heavy
electron compound CeCoIn5 which is superconducting below 2.3 K but does not show
any magnetic ordering of the localized Ce-moments. CeCoIn5 belongs to a class of
heavy fermion cerium compounds with a non-magnetic ground and exhibits a
metamagnetic transition characterized by a sharp rise in the magnetization at low
temperatures at a characteristic critical magnetic field . A typical example for this is
CeRu2Si2. In addition to this feature, invariably a peak in the linear susceptibility is
observed at a characteristic temperature T1 which is found to correlate well with this
critical field. CeCoIn5 appears to stand as an exception apparently violating this
“standard” heavy electron non-magnetic behavior. We have performed a detailed linear
and nonlinear susceptibility measurements and analyzed the susceptibility data with a
single energy scale model [1], which explains the observed correlations in heavy
fermion metamagnets quite well.
Reference:
[1] B. S. Shivaram, D. G. Hinks, M. B. Maple, M. A. deAndrade and P. Kumar, Phys.
Rev. B. 89 (2014) 241107(R)
126
Mo-P007
Stadium
Mo 13:30-15:30
Superfluid density in the Heavy Fermion Superconductor
Ce1-xYbxCoIn5 studied by Muon Spin Relaxation/Rotation
Z. F. Ding1, J. Zhang1, C. Tan1, K. Huang1, I. Lum2, O. O. Bernal3, P.-C. Ho4, D. E.
MacLaughlin5, M. B. Maple2, L. Shu1
1
Department of Physics and State Key Laboratory of Surface Physics, Fudan University,
Shanghai, China
2
Department of Physics, University of California, San Diego, La Jolla, California,USA
3
Department of Physics and Astronomy, California State University, Los Angeles, California,
USA
4
Department of Physics, California State University, Fresno, California, USA
5
Department of Physics, University of California, Riverside, California, USA
Magnetic penetration depth in the heavy fermion system Ce1-xYbxCoIn5 (x = 0, 0.05,
0.125, 0.2, 0.3, 0.4 and 0.5) was measured by muon spin relaxation/rotation (μSR) and
absolute values of superfluid density at zero temperature were calculated. Substitution
of Ce with Yb leads to fast decreasing of superfluid density until the critical
concentration x = 0.2, where Fermi surface changes. Superfluid density decreases
slightly with more Yb is substituted when x> 0.2. Temperature dependence of
superfluid density suggested d-wave superconductivity for all measured samples.
127
Mo-P008
Stadium
Mo 13:30-15:30
Universal heat conduction in Ce1−xYbxCoIn5: Evidence for robust
Nodal d-wave superconducting gap
Y. Xu1, J. K. Dong1,2, I. K. Lum3, J. Zhang1, X. C. Hong1, L. P. He1, K. F. Wang4, Y. C. Ma4, C.
Petrovic4, M. B. Maple3, L. Shu1,5, and S. Y. Li1,2,5
1
State Key Laboratory of Surface Physics and Department of Physics, Fudan University,
Shanghai200433, China
2
Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
3
Department of Physics and Center for Advanced Nanoscience, University of California, San
Diego, La Jolla, California 92093, USA
4
Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory,
Upton, New York 11973, USA
5
200433, China
In the heavy-fermion superconductor Ce1−xYbxCoIn5, Yb doping was reported to
cause a possible change from nodal d-wave superconductivity to a fully gapped d-wave
molecular superfluid of composite pairs near x ≈ 0.07(nominal value xnom=0.2). Here
we present systematic thermal conductivity measurements on Ce1−xYbxCoIn5 (x =
0.013, 0.084, and 0.163) single crystals. The observed finite residual linear term κ0/T is
insensitive to Yb doping, verifying the universal heat conduction of the nodal d-wave
superconducting gap in Ce1−xYbxCoIn5. Similar universal heat conduction is also
observed in the CeCo(In1−yCdy)5 system. These results reveal a robust nodal d-wave
gap in CeCoIn5 upon Yb or Cd doping.
Reference:
[1] Y. Xu et al., arXiv: 1510.04520 (Phy. Rev. B, in press).
128
Mo-P009
Stadium
Mo 13:30-15:30
Superconducting Upper Critical Field of Zn-Doped CeCoIn5
M. Yokoyama1, H. Mashiko1, R. Otaka1, K. Tenya2, A. Kondo3, K. Kindo3, Y. Kono3,
Y. Shimizu3, T. Sakakibara3
1
Faculty of Science, Ibaraki University, Mito, Japan
Faculty of Education, Shinshu University, Nagano, Japan
3
Institute for Solid State Physics, University of Tokyo, Kashiwa, Japan
2
We report the effect of Zn doping on upper critical field Hc2 of the Pauli-limited
superconductor CeCoIn5. In the mixed compounds CeCo(In1-xZnx)5, it is found that
doping Zn suppresses the superconducting (SC) transition temperature Tc and then
generates the antiferromagnetic (AFM) order above x~0.05 [1]. The present
investigation using thermal, transport and magnetic measurements reveals unusual
robust x dependence of Hc2 in contrast with the monotonic reduction of Tc. In particular,
both the tetragonal a- and c-axis Hc2 are nearly unchanged up to 5% doping of Zn into
CeCoIn5, whereas Tc at the corresponding Zn concentration is reduced to 80% of that
for x=0. We consider that this feature is ascribed to a relaxation of the Pauli
paramagnetic suppression in Hc2 as a consequence of a combination of both an
enhanced AFM correlation and a reduced SC condensation energy in these alloys.
Reference:
[1] M. Yokoyama et al., J. Phys. Soc. Jpn. 83, 033706 (2014); Phys. Rev. B 92, 184509
(2015).
129
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Superconductivity and non-Fermi liquid behavior in Ce(Co1-xNix)In5
R. Otaka1, M. Yokoyama1, H. Mashiko1, T. Hasegawa1, K. Tenya2, Y. Kono3, Y.
Shimizu3, Y. Ikeda3, H. Yoshizawa3, T. Sakakibara3
1
Faculty of Science, Ibaraki University, Mito, Japan
Faculty of Education, Shinshu University, Nagano, Japan
3
2
The heavy-fermion superconductor CeCoIn5 has been attracting much interest
because of anomalous superconducting (SC) property and its interplay with non-Fermi
liquid (NFL) behavior [1]. It is presently considered that the antiferromagnetic (AFM)
quantum criticality involved in the vicinity of the SC order is responsible for the
evolution of the NFL anomaly [2]. In the present investigation for the mixed alloys
Ce(Co1-xNix)In5, we reveal that doping Ni into CeCoIn5 monotonically suppresses the
SC transition from 2.3 K (x=0) to < 0.5 K (x=0.25), but does not generate the AFM
order in contrast with the situation seen in the other doped alloys such as Ce(Co,Rh)In5
[3]. At x=0.25, in particular, specific heat divided by temperature C/T exhibits the NFL
behavior characterized by a –lnT divergence, suggesting that the quantum critical
fluctuation is still dominant in the normal and paramagnetic state of Ce(Co1-xNix)In5.
Reference:
[1] C. Petrovicet al., J. Phys:.Condens. Matter 13, L337 (2001).
[2] L. D. Pham et al., Phys. Rev. Lett. 97, 056404 (2006).
[3] V. S. Zapf et al., Phys. Rev. B 65, 014506 (2001).
130
Mo-P011
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Microscopic Investigation of Electronic heterogeneity Induced by
Substitutions in a Quantum Critical Metal CeCoIn₅
H. Sakai1, F. Ronning2, J. -X. Zhu2, N. Wakeham2, H. Yasuoka2, T. Hattori1, Y. Tokunaga1,
S. Kambe1, E. D. Bauer2, and J. D. Thompson2
1Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-
1195, Japan
2 Los Alamos National Laboratory, Los Alamos, NM, USA
Heavy fermion superconductor CeCoIn5 is known to lie in close proximity to an
antiferromagnetic (AFM) quantum critical point (QCP) at ambient pressure [1, 2]. A
small amount of Cd substitution for In induces long range AFM order [3]. Applying
pressure suppresses the AFM; however, the fluctuations and the signatures at this
pressure induced AFM QCP are absent [4]. By means of the nuclear quadrupole
resonance (NQR) technique, it is microscopically probed that Cd substitutions
intrinsically produce an electronic heterogeneous state, i.e., unchanged f states as if in
the pure CeCoIn5 and locally bound f states in the vicinity of Cd substituents [5].
Reference:
[1] C. Petrovic et al., J. Phys.: Condens. Matter 13, L337 (2001).
[2] H. Sakai et al., Phys. Rev. Lett. 107, 137001 (2011).
[3] L. D. Pham et al., Phys. Rev. Lett. 97, 056404 (2006).
[4] S. Seo et al., Nature Phys. 10, 120 (2014).
[5] H. Sakai et al., Phys. Rev. B 92 121105(R) (2015).
131
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Point-Contact Spectroscopy on Heavy Fermion
L.−Q. Che1, 𝑌. −𝐽. 𝑍ℎ𝑎𝑛𝑔1, 𝐷. 𝐺𝑛𝑖𝑑𝑎2, D. Kaczorow2, H. S. Jeevan1, H.Q. Yuan1,3,
Hanoh Lee1, Xin Lu1,3
1
Hangzhou, 310058,China
2
Institute of Low Temperature and Structure Research, Polish Academy of Sciences,
Wroclaw, Poland
3
Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093,
China
We report point-contact spectroscopic studies on heavy Fermion CeCoIn5 , Ce2PdIn8
and CeCu2Si2 single crystals for comparison. They all exhibit common Fano-like
conductance spectra below the coherence temperature T∗. Contrast to CeCoIn5 and
Ce2PdIn8, CeCu2Si2 exhibits another asymmetric conductance structure at around ±
30mV, indicating a hybridization gap caused by Kondo hybridization. CeCoIn5 and
Ce2PdIn8 show a similar sloping background, while the background of CeCu2Si2 is a
typical V-shape. The common Fano-like conductance spectra indicate the development
of hybridization between local f and itinerant conduction electrons for heavy fermions
below T∗.
132
Mo-P013
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Optical spectroscopy study of heavy fermion compound CePt2In7
R. Y. Chen1, S. J. Zhang1, E. D. Bauer2, J. D. Thompson2, N. L. Wang1,3
1
International Center for Quantum Materials, School of Physics, Peking University, Beijing,
China
2
Los Alamos National Laboratory, Los Alamos, New Mexico, USA
3
Collaborative Innovation Center of Quantum Matter, Beijing, China
The heavy fermion compound CePt2In7 is a more two dimensional analogy of the
famous "115" materials CeMIn5. It experiences an antiferromagnetic phase transition
at 5.2 K, which could be suppressed by pressure and gives way to superconductivity.
We performed infrared spectroscopy measurement on CePt2In7. The measurement
revealed a very weak hybridization gap feature in optical conductivity spectrum at 8 K.
The energy scale of this gap was identified to be 20 meV, much smaller than the
CeCoIn5 compound. The results indicate weaker hybridization strength between the
conduction band and Ce 4f level, being consistent with the antiferromagnetic ground
state. We also conducted optical pump-probe spectroscopy to study the ultrafast
quasiparticle dynamics in this compound. The pump induced transient reflectivity ΔR/R
increases with temperature decreasing until 100 K, where an additional relaxation
channel gradually shows up. Both the amplitude and relaxation time of this channel
keeps increasing upon cooling until the lowest temperature, which agrees well with the
expected behavior of heavy electrons relaxing across a hybridization gap. In contrast
with CeCoIn5 whose relaxation dynamics could be well described by a single
exponential decay, the multiple exponential decay of CePt2In7 might be related to the
weaker hybridization strength, being similar to some antiferromagnetic heavy fermion
compounds.
133
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The Q-phase of CeCoIn5 and theories of Paul-limited
superconductors at high magnetic fields
M. Kenzelmann1
1
Laboratory for Scientific Developments and Novel Materials, Paul Scherrer Institut, CH5232 Villigen, Switzerland
I will present an overview of the history of theories that describe Pauli-limited
superconductors at high magnetic fields. I will discuss how these theories relate to the
observation of the high-field Q-phase observed in CeCoIn5 [1].
Reference:
[1] S. Gerber, M. Bartkowiak, J.L. Gavilano, E. Ressouche, N. Egetenmeyer, C.
Niedermayer, A.D. Bianchi, R. Movshovich, E.D. Bauer, J.D. Thompson and M.
Kenzelmann, Switching of magnetic domains reveals evidence for spatially
inhomogeneous superconductivity, Nature Physics 10, 126 (2014) and references
therein.
134
Mo-P015
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YbNi4(P1-xAsx)2: Single crystal growth by the Czochralski method
K. Kliemt1 , C. Krellner1
1
Institute of Physics, Goethe-University Frankfurt, D-60438 Frankfurt, Germany
With TC = 0.17 K, the ferromagnetic material YbNi4P2 has the lowest Curie
temperature ever observed among stoichiometric compounds [1]. The rare case of a
quantum critical point occurs in the substitution series YbNi4(P1-xAsx)2 at x~0.1 [2].
Due to the high volatility of the constituents, the crystal growth is performed in
closed crucibles. In the past, needle shaped crystals of several mm in length have been
grown by the Bridgman method from a Ni-P self-flux. The melt is agressive and attacks
all tested crucible materials. This leads to a contamination of the melt and of the crystals
as well.Here, we present the growth of YbNi4P2 single crystals from a levitating melt
by the Czochralski method. This method is crucible free and cm-sized oriented single
crystals can be grown. The samples were characterized by electrical transport and
magnetization measurements. Furthermore, we investigated the homogenity of the As
distribution in the crystals of the substituted compound.
Fig.1: YbNi4P2 single crystal grown by
The Czochralski method.
Fig.2: Sharp Laue reflexes prove the
good crystallinity of the sample.
References:
[1] C. Krellner et al., New J. Phys. 13, 103014 (2011)
[2] A. Steppke et al., Science 339, 933 (2013).
135
Mo-P016
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Single crystal growth and physical properties of heavy fermion
antiferromagnet YbNi2Si2
Y. Matsumoto1, Y. Nakamura1, S. Ohara1, Y. Haga2, Z. Fisk2,3, Y. Kono4, S.
Nakamura4, S. Kittaka4, T. Sakakibara4
1Department of Engineering Physics, Electronics and Mechanics, Nagoya Institute of
Technology, Nagoya, Aichi, Japan
2
Advanced Science Research Center, Japan Atomic Energy Agency,Tokai,Ibaraki, Japan
3
4
Institute for Solid State Physics, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba, Japan
The YbNi2Si2 with tetragonal ThCr2Si2-type structure (space group I4/mmm) has
been prepared by arc melting method and its physical properties have been measured
only by poly crystal sample.[1] YbNi2Si2 is the antiferromagnet with antiferromagnetic
temperature TN =2.3 K and propagation vector q = (0, 0, 0.8025).
We have successfully synthesized the single crystal of YbNi2Si2 using Sn flux
method and measured the resistivity, magnetic properties and heat capacity of
YbNi2Si2 in low temperature. It is found that the susceptibility follows Curie-Weiss
low from room temperature to about 100 K, indicating that the valence of Yb is about
3+ in high temperature and the TN of single crystal YbNi2Si2 is 1.3 K and the electronic
specific heat coefficient  is about 1 J/mol K2. The metamagnetic transition takes place
about HC = 0.1 T when a magnetic field is applied for [001], [110] [100] direction,
indicating that the magnetic anisotropy is small. Moreover, there is no enhancement of
g around HC and the  monotonously decreases with increasing magnetic field.
Reference:
[1]G. Andre et al., J. Alloys Comp. 224, 253 (1995).
136
Mo-P017
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Crystallographic, magnetic, thermal and electric transport properties
in heavy fermion YbPd2Si2 single crystal
Y. Matsumoto1, Y. Haga2, Z. Fisk2,3, S. Ohara1
1
Department of Engineering Physics, Electronics and Mechanics, Nagoya Institute of
Technology, Nagoya, Aichi, Japan
2
Advanced Science Research Center, Japan Atomic Energy Agency,Tokai,Ibaraki, Japan
3
The YbPd2Si2 with tetragonal ThCr2Si2-type structure (space group I4/mmm) has
been prepared by arc melting method and its physical properties have been measured
only by poly crystal sample. YbPd2Si2 is a heavy fermion compounds with the
electronic specific coefficient γ = 200 mJ/mol K2 and its Yb valence is 2.83+ [1, 2].
Moreover, the magnetic order is observed above about 1 GPa [3].
We have successfully synthesized the single crystal of YbPd2Si2 using Sn flux
method. The chemical composition and homogeneity of samples were confirmed by the
electron probe micro analyzer. The crystal structure of samples was determined by the
single crystal and powder X-ray method. We have measured the electrical resistivity,
heat capacity and magnetic properties. It is found that the effective mass enhancement
of single crystal of YbPd2Si2 is about half than that of poly crystal of YbPd2Si2 and the
magnetization for B//[001] is about twice larger than that for B//(001).
Reference:
[1]H. Yamaoka et al. : Phys. Rev. B 82,035111 (2010).
[2]S. K. Dhar et al., Solid State Commun. 61, 478 (1987).
[3]T. Nakano et al., Solid State Commun. 132, 325 (2004).
[4]P. Bonville et al., J. Magn. Magn. Marer. 97, 178 (1991).
E-mail for corresponding author: [email protected]
137
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Quantum Multicritical Point in YbRh2Si2
M. Brando1, S. Hamann1, J. Zhang1,2, D. Jang1, A. Hannaske1, L. Steinke1,3, S. Lausberg1, L.
Pedrero1, C. Klingner1, C. Geibel1, C. Krellner4
1
Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
2
Center of Correlated Matter, Zheijiang University, 310058 Hangzhou, China
3
Condensed Matter Physics and Materials Science Department, Brookhaven National
Laboratory, Upton, New York 11973, USA
4
Institute of Physics, Goethe University Frankfurt, D-60438 Frankfurt am Main, Germany
During the last few decades, the existence of quantum critical points (QCPs) has been
verified in low-temperature antiferromagnets like YbRh2Si2 which has a transition
temperature of 70 mK. In this material the QCP can be induced by a small magnetic
field ( B) applied both along the crystallographic c-axis (B∥c) or within the ab-plane
(B⊥c). The nature of this QCP is undoubtedly not conventional and still under strong
debate. Investigations on the Co-substituted YbRh2Si2 provide solid basis of evidence
that the nature of the QCP in YbRh2Si2 with B ∥c is very different from that with B⊥c.
In fact, with B∥c, the QCP is the endpoint of a first order transition line (see figure) and
it is therefore a quantum multicritical point (QMP). Such a situation has never been
observed in any material before and it is in excellent agreement with the theory
proposed by Misawa et al. [1].
Reference:
[1] T. Misawa, Y. Yamaji, and M. Imada, JPSJ 77, 093712 (2008).
138
Mo-P019
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Evolution of Ferromagnetism to Antiferromagnetism in
Yb(Rh1−x Cox)2Si2
S. Hamann1, J. Zhang1,2, D. Jang1, A. Hannaske1, L. Steinke1,3, S. Lausberg1, L. Pedrero1, C.
Klingner1, C. Geibel1, C. Krellner4 , M. Brando1
1
2
Center of Correlated Matter, Zheijiang University, CHN-310058 Hangzhou, China
3
4
Condensed Matter Physics and Materials Science Department, Brookhaven National
Institute of Physics, Goethe University Frankfurt, D-60438 Frankfurt am Main, Germany
The heavy-fermion system YbRh2Si2 is one of the most disputed case in the field of
quantum criticality. Despite intensive studies, the nature of its ground state is rather
unclear. Because of its huge crystalline electric field (CEF) induced anisotropy, the very
weak antiferromagnetic (AFM) order for T<TN = 70 mK was assumed to be connected
with moments lying in the basal plane, the easy CEF direction. However, recent results
for a 27% Co-substituted sample surprisingly evidenced ferromagnetic (FM) order with
moments along the CEF hard direction (c-axis) [1], raising again the question about the
nature of the magnetic ordered state in pure YbRh2Si2. Based on ac-susceptibility,
magnetization, specific heat and magnetoresistance measurements on single crystals of
Yb(Rh1−xCox)2Si2, we resolved the magnetic phase diagram for 0 ≤ x ≤ 0.27 (see figure).
It displays an evolution from the FM state at x = 0.27 to a canted AFM and then a pure
AFM state with decreasing x. Features observed in different properties give some hints
on the orientation of the ordered moments as well as the orientation of the propagation
vector.
Reference:
[1] S. Lausberget al., PRL 110, 256402 (2013).
139
Mo-P020
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Sb-NMR/NQR studies of heavy fermion system YbRhSb
Y. Kishimoto, H. Tou, , Y. Awai, H. Kotegawa, Y. MuroA, K. NakamuraB, M. SeraB, T.
TakabatakeB
1
2
3
Department of Physics, Kobe University, Kobbe, 657-8501, Japan
Liberal Arts and Sciences, Toyama Prefectural University, Izumi 939-0398, Japan
Graduate School of AdS Matter, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
4
IAMR, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
Orthorhombic YbRhSb shows a ferromagnetic transition at TM=2.7 K with a tiny
spontaneous moment 3×10-3μB/Yb along all three principal directions from magnetic
susceptibility, magnetization and specific heat measurements. Isothermal
magnetization measurement reveals a metamagnetic transition at 2.2 T for field parallel
to b-axis. At present weak ferromagnetism originates from a sort of canted AFM state.
In order to investigate the magnetic ordered state from a microscopic point of view, we
have carried our Sb-nuclear magnetic resonance (NMR) and nuclear quadrupole
resonance (NQR) for YbRhSb. We successfully observed all Sb NQR lines
(±1/2⇔±3/2) line and (±3/2⇔±5/2) line for 121Sb nucleus( I=5/2), and (±1/2⇔±3/2),
(±1/2⇔±3/2) , and (±3/2⇔±5/2) line for 123Sb nucleus (I=7/2). Below TM, only the (±
1/2⇔±3/2) line splits into two line due to internal field. Together with Sb-NMR results,
we found that Yb magnetic moments lie antiferromagnetically along b-axis with
moment of 0.1-0.3 μB/Yb. Our results suggest that the observed ferromagnetic moment
arises from the ferromagnetic component of the canted AF state.
140
Mo-P021
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Electrical Resistivity of Yb3Os4Ge13 under Pressure
Yajian Hu1, Y. W. Cheung1, H. C. Liu1, Y. G. Shi2, Y. F. Yang2,3, S. K. Goh1
1
2
Department of Physics, The Chinese University of Hong Kong, China
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics,
Chinese Academy of Science, Beijing, China
3
The rare-earth quasi-skutterudite R3T4X13 shows a variety of exotic properties such
as heavy fermion behavior and magnetic orders. Electrical resistivity measurement on
Yb3Os4Ge13 shows a normal metallic behavior at high temperature followed by a
logarithmic divergence at low temperature. The low temperature upturn can be
gradually suppressed with increasing magnetic field, indicating a possible Kondo
contribution below T* ~ 40 K [1]. To understand the low temperature state, we measure
the electrical resistivity under hydrostatic pressure and high magnetic field. We will
present the pressure evolution of the resistivity over a wide temperature and field range,
allowing us to follow the fate of T*. The mechanism responsible for the low temperature
behavior of the electrical transport will be discussed.
Reference:
[1] C. L. Yang et al., Phys. Rev. B 91, 075120 (2015)
141
Mo-P022
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Physical properties of single crystalline YbCo6Ge6
YongjunZhanga, Fei Gaoa, ChunyuGuoa, YunfengWanga, WenbingJianga, HanohLeea, Huiqiu
Yuana, Horst Borrmannb, Yuri Grinb, Frank Steglicha
a
Center for correlated matter, Zhejiang University, Hangzhou, Zhejiang, China
b
Max-Planck institute for chemical physics of solids, Dresden, Germany
We present the synthesis, crystal structure identification,and physical property
studies on the single crystal compounds of YbCo6Ge6 (P6/mmm, YCo6Ge6 structure
type).YbCo6Ge6 displays broad and large enhancement of the specific heat coefficient
developed below 10K down to 1K, followed by a broad peak-like feature below 1K
with the peak position of 0.55K, indicating possible enhancement of fluctuation near
its transition that is close to zero temperature. The temperature dependence of the
resistivity data, however, shows good metallic behavior with moderate Kondo effect,
rather typical behavior of localized Kondo lattice system. The origin of the large
specific heat coefficient and the broad peak at around 0.55K will be discussed with
magnetic, thermal, and transport properties.
Reference:
Corresponding author :Hanoh Lee
Email :[email protected]
142
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Unusual Yb Magnetic Properties in YbMn6Ge6-xSnx Studied by ESR
V. A. Ivanshin1, M. Hemmida2, H.-A. Krug von Nidda2, N. A. Ivanshin3, T. Mazet4, D.
Malterre4,M. Francoiş4
1
2
Institute of Physics, Kazan Federal University, Kazan, Russia
EP V, Center for Electronic Correlations and Magnetism, University of Augsburg, Augsburg,
Germany
3
Kazan State University for Architecture and Engineering, Kazan, Russia
4
Insitit Jean Lamour, Universitéde Lorraine, Vandœuvre-lés-Nancy, France
In intermetallic solids, the 4f states of ytterbium can hybridize more or less strongly
with other valence electrons (f-spd hybridization) to yield a complex electronic
structure and intermediate valence [1]. The YbMn6Ge6−xSnx compounds (x = 4.2 and
4.4) have been investigated by means of magnetic measurements, resonant inelastic xray scattering, and electron spin resonance (ESR) spectroscopy over the temperature
range 4.2-300 K. The temperature evolution of ESR parameters clearly reflects the
unusually high magnetic ordering temperature of Yb (60 and 90 K for x = 4.2 and 4.4,
respectively), a co-existence of ESR signals which can be ascribed to the Yb3+ and
manganese ions, and ordering of Mn moments with increasing temperature. The
strong Mn-Yb exchange interaction which enhances the intermediate valent Yb
magnetic ordering temperature and allows for extending the stability domain of the Yb
magnetic order towards lower Yb valence [2] is discussed.
Reference:
[1] V. A. Ivanshin et al., JETP Lett. 99, 153 (2014)
[2] T. Mazet et al., PRB 92, 075105 (2015)
143
Mo-P024
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Magnetic Anisotropy in GdRh2Si2 studied by ESR
J. Sichelschmidt1, K. Kliemt2, C. Krellner2, C. Geibel1
1
Max Planck Institute for Chemical Physics of Solids, Dresden,Germany
2
Institute of Physics, University of Frankfurt, Frankfurt, Germany
One of the exceptional magnetic properties in the heavy fermion metal YbRh2Si2 is
the presence of an Electron Spin Resonance (ESR) signal that appears as a
consequence of the Kondo interaction despite the strong magnetic anisotropy [1].
In contrast the structural homologue GdRh2Si2 shows a weak magnetic anisotropy
due to the pure S Gd-ground state.
The magnetic properties in the antiferromagnetic (AFM) ordered state of GdRh2Si2
[2] are investigated by ESR spectroscopy at 9.4 and 34 GHz on high-quality single
crystals. The almost isotropic Gd3+ resonance field in the paramagnetic regime becomes
strongly anisotropic in the AFM ordered region below 107 K because of strong internal
anisotropic exchange-fields. Furthermore, the ESR anisotropy is strongly frequency
dependent, i.e. dependent on the applied field, in agreement with the anisotropic
behavior of the magnetization [2]. The anisotropy constants could be extracted from an
analysis within a mean-field model.
Reference:
[1] B. Kochelaev et al., Eur. Phys. J. B 72, 485 (2009)
[2] K. Kliemt and C. Krellner, J. Cryst. Growth 419, 37 (2015)
144
Mo-P025
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Robust and tunable itinerant ferromagnetism at the silicon
surface of antiferromagnet GdRh2Si2
C. Krellner1, K. Kliemt1, S. Witt1, M. Guettler2, A. Generalov3, K. Kummer4, C.
Geibel5, C. Laubschat2, and D. V. Vyalikh2,6
1
2
Physikalisches Institut, Goethe-Universität Frankfurt, 60438 Frankfurt/Main, Germany
Institute of Solid State Physics, Dresden University of Technology, 01062 Dresden, Germany
3
MAX-Laboratory, Lund University, 22100 Lund, Sweden
4
European Synchrotron Radiation Facility, Grenoble, France
5
Max Planck Institute for Chemical Physics of Solids, 01187 Dresden,Germany
6
IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain
Among the ternary silicides of the series LnRh2Si2 (Ln = Ce-Nd, Sm-Yb) which crystallize in the
bodycentered tetragonal ThCr2Si2 structure, the change of the rare earth element leads to a drastic
change of magnetic properties. All compounds order antiferromagnetically but their Néel
temperatures, for example, vary over a wide temperature range between 70 mK (YbRh2Si2 [1]) and
107 K (GdRh2Si2 [2]). Up to now, most interest was focused on CeRh2Si2 and YbRh2Si2 because of
their strong correlation effects. However, recently new interest emerged because of surface states
presenting interesting magnetic properties. Here, we present first results to tune the surface
magnetism by changing the rare earth elements.
We obtained platelet-shaped single crystals in this series (Ln = Sm, Gd, Ho, Yb) using a modified
Bridgman method up to 1500°C together with a metallic solvent (indium) in closed crucibles [3].
The magnetic ground state of the respective crystals was characterized using magnetization,
specific-heat and electrical transport measurements.
Applying angle-resolved photoelectron spectroscopy (ARPES), we could demonstrate that the
silicon surface of GdRh2Si2 bears two distinct two-dimensional electron states that are created by
Shockley and Dirac fermions. Both are subject to strong exchange interaction with the ordered 4f
moments lying underneath the Si-Rh-Si trilayer. The bulk Néel temperature TN ~ 107 K of
GdRh2Si2 marks the onset of in-plane ferromagnetic alignment of the Gd 4f moments, which stack
antiferromagnetically along the c-axis [2]. The magnetic interaction between these ferromagnetic
Gd-layers and the surface states lifts up the spin degeneracy of the latter, leading to the appearance
of spin-split subbands with largest splitting values of 185 meV and 70 meV for the Shockley and
Dirac state, respectively [4].
References:
[1]
[2]
[3]
[4]
O. Trovarelli et al., Phys. Rev. Lett. 85, 626 (2000).
K. Kliemt, C. Krellner, J. Crystal Growth 419, 37 (2015).
C. Krellner et al., Phil. Mag. 92, 2508 (2012).
M. Guettler et al., submitted (2015).
145
Mo-P026
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Local Kondo Entanglement and Symmetry Protected Local
Quantum Criticality
J. Dai1 and X. Y. Feng1
1
Department of Physics, Hangzhou Normal University, Hangzhou 310036, China
Local Kondo entanglement (LKE) is defined as the concurrence of a short-ranged
Kondo singlet state consisting of a localized magnetic moment and its nearby
conduction electron. We derive the entanglement phase diagram for an effective twoimpurity Kondo model and show that the LKE vanishes exactly at the two-impurity
quantum critical point. We further extend this result for a Kondo lattice model with a
hidden particle-hole symmetry. Our results demonstrate the existence of a class of
symmetry-protected local quantum critical points in Kondo systems signaled by the
LKE breakdown.
Reference:
[1] Y. Li et al., arXiv: 1503.05091.
[2] J. Dai et al., in preparation, 2016.
146
Mo-P027
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Scaling behavior of the strong-coupling fixed point of the
pseudogap Kondo model
F. Wu1,* and S. Kirchner1,ϯ
1
Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou,
310027, China
Scaling functions have been proven useful in the analysis of critical phenomena and
reflect the nature and symmetry of the underlying fixed point. The strong-coupling
fixed point of the Kondo impurity model possesses a dynamical spin susceptibility χ(τ,
T)which turns into a simple power law in terms of Tτ0/ sin(πτT) in the vicinity of the
strong-coupling fixed point, where 0 is proportional to the density of states at the Fermi
energy (T is temperature andτ is imaginary time). This behavior is an immediate
consequence of the conformal symmetry underlying Hamiltonian. We analyze the
scaling properties of the strong-coupling fixed points in the single impurity pseudogap
Anderson model at particle-hole symmetry. In this model, the density of states of
conduction electron states vanishes in a power-law fashion at the Fermi energy. As a
result, the underlying Hamiltonian no longer possesses conformal symmetry. In
particular, the conduction electron T-matrix and dynamical spin susceptibility scaling
functions are studied and compared to those of the quantum critical point of this model,
which separates a Kondo-screened phase from a free local moment phase. This is
accomplished using the strong-coupling version of the continuous-time quantum Monte
Carlo algorithm (CT-QMC) where a perturbative expansion of the partition function in
terms of the impurity-host hybridization is stochastically sampled. Our results allow us
to infer if ω/T -scaling is present or absent at the strong-coupling fixed point.
Emails: [email protected] or [email protected]
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Kondo vs Majorana-type signatures in the Andreev transport
T. Domanski,
1Institute of Physics, M. Curie-Sklodowska University, 20-031 Lublin, Poland
In most of the bulk materials superconductivity usually competes with any magnetic
ordering and vice versa the magnetism has detrimental influence on superconducting
order. We show, however, that in nanoscopic hetero-structures the electron pairing may
constructively support the magnetic ordering. Such situation would be possible to
achieve at low temperatures in the quantum dots coupled to the metallic and
superconducting reservoirs, where the proximity induced electron pairing cooperates
with the correlations enhancing the spin-exchange interactions. The resulting Kondo
resonance (observable by the zero-bias feature in the Andreev conductance [1]) is thus
significantly enhanced by the superconducting lead. We explain this intriguing
tendency adopting the Schrieffer-Wolff canonical transformation, the second order
perturbative treatment of the Coulomb repulsion, and the nonperturbative numerical
renormalization group calculations [2]. Furthermore, we confront this zero-bias subgap
enhancement with similar effect caused by the Majorana-type quasiparticles in the STM
measurements with the normal (conducting) tip probing the electronic states of atomic
chain deposited on the superconducting substrate in presence of the Zeeman and Rashba
interactions [3]. We propose possible means to distinguish between these two physical
effects giving rise to the zero-bias anomaly of the subgap conductance.
Reference:
[1] R.S. Deacon et al., Phys. Rev. Lett. 104, 076805 (2010).
[2] T. Domanskiet al., arXiv:1507.01851v2 (2015).
[3] S. Nadj-Pergeet al., Science 346, 602 (2014).
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Efficient implementation of the parquet equations – role of the
reducible vertex function and its kernel approximation
Gang Li1, Nils Wentzell1, 2, Petra Pudleiner1, Patrik Thunström1 and Karsten Held1
1
2
Institute of Solid State Physics, Vienna University of Technology, A-1040 Vienna, Austria
Institut für Theoretische Physik and CQ Center for Collective Quantum Phenomena, Universität
Tübingen, Auf der Morgenstelle 14, 72076 Tübingen, Germany
We present an efficient implementation of the parquet formalism, which respects the
asymptotic structure of the vertex functions at both single- and two-particle levels in
momentum- and frequency-space. We identify the two-particle reducible vertex as the
core function, which is essential for the construction of the other vertex functions. This
observation stimulates us to consider a two-level parameter-reduction for this function
to simplify the solution of the parquet equations. The resulting functions, which depend
on fewer arguments, are coined “kernel functions”. With the use of the “kernel
functions”, the open boundary of various vertex functions in the Matsubara-frequency
space can be faithfully satisfied. We justify our implementation by accurately
reproducing the dynamical mean-field theory results from momentum-independent
parquet calculations. The high-frequency asymptotic of the single-particle self-energy
and the two-particle vertex are correctly reproduced, which turns out to be essential for
the self-consistent determination of the parquet solutions. The current implementation
is also feasible for the dynamical vertex approximation.
Reference:
[1] G. Li et al., arXiv:1510.03330 (2015)
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Finite-temperature Dynamics and Quantum Criticality in a Model
for Insulating Magnets
Jianda Wu1 , Wang Yang1 , Congjun Wu1, Qimiao Si2
1
2
UCSD
Rice University
Theoretical understanding of the finite-temperature dynamics in quantum critical
systems is a challenging problem, due to the mixing of thermal and quantum
fluctuations. Recently, neutron scattering experiments in the three-dimensional
quantum dimmer material TlCuCl3 under pressure tuning have mapped out the
magnetic dynamics at finite temperatures in the quantum critical regime [1], thereby
providing the opportunity for systematic understandings. In this work, we calculate the
spin spectral function of an O(n) symmetric field theory using a field-theory procedure
to two loops. We calculate the temperature dependence of the energy and damping rate
of the spin excitations in the quantum critical regime, demonstrate a good agreement
with the experimental results, and determine the parameter regime of the field theory
that is appropriate for TlCuCl3. From our calculations we can also suggest further
experimental means to test the applicability of the underlying field theory in this and
related systems.
Reference:
[1] P. Merchant, B. Normand, K.W. Krämer, M. Boehm, D. F. McMorrow and Ch.
Rüegg, Nat. Phys. 10, 373 (2014).
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Fermion-induced quantum critical points: type-II Landau-forbidden
transitions
Zi-Xiang Li1, Yi-Fan Jiang1, 2, Shao-Kai Jian1, and Hong Yao1
1
2
Institure for Advanced Study, Tsinghua University, Beijing 100084, China
Department of Physics, Stanford University, Stanford, California 94305, USA
According to Landau criterion, phase transitions must be first-order when cubic
terms of order parameters are allowed by symmetry in the Landau-Ginzburg free energy.
Here, from renormalization group (RG) analysis we show that second-order quantum
phase transitions can occur at such putatively first-order transitions in strongly
interacting two-dimensional Dirac semimetals. As such type of Landau-forbidden
quantum critical points are induced by gapless fermions, we call them “fermioninduced quantum critical points” (FIQCP), which are type-II Landau-forbidden
transitions. We further introduce a sign-problem-free model of SU(N) fermions on the
honeycomb lattice featuring a transition between Dirac semimetals and Kekule valence
bond solids. Remarkably, our large-scale Majorana quantum Monte Carlo simulations
show convincing evidences of a continuous quantum phase transition for N = 2, 3, 4, 5,
and 6, consistent with the RG analysis. We also discuss possible experimental
realizations of the FIQCP in graphene-like materials.
Reference:
[1] Z.-X. Li, Y.-F. Jiang, S.-K. Jian, and H. Yao, arXiv: 1512.07908 (2015).
[2] Z.-X. Li, Y.-F. Jiang, and H. Yao, Phys. Rev. B 91, 241117 (2015) (Editor’s
Suggestion).
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Sign-problem-free Majorana-quantum-Monte-Carlo studies of
quantum critical phenomena of Dirac fermions in two
dimensions
Zi-Xiang Li1, Yi-Fan Jiang1, Hong Yao1
1
Quantum critical phenomena may be qualitatively different when massless Dirac
fermions are present at criticality. Using recently-discovered fermion-sign-free
Majorana quantum Monte Carlo (MQMC) method introduced by us in Ref. [1-3], we
investigate two quantum critical phenomena on the honeycomb lattice including
spinless Dirac fermions at their charge-density-wave (CDW) phase transitions and the
charge-4e to charge-2e superconductor phase transition of a minimal charge-4e
superconducting “mean-field" model. By nite-size scaling, we accurately obtain critical
exponents of this so-called Gross-Neveu chiral-Ising universality class of two and four
(components) Dirac fermions in 2+1D, which are qualitatively different from the meanfield results but are reasonably close to the ones obtained from renormalization group
calculations.
Reference:
[1] Zi-Xiang Li, Yi-Fan Jiang, and Hong Yao, Phys. Rev. B 91, 241117(R) (2015) ;
(Editors' Suggestion).
[2] Zi-Xiang Li, Yi-Fan Jiang, and Hong Yao, New J. Phys. 17, 085003 (2015).
[3] Zi-Xiang Li, Yi-Fan Jiang, and Hong Yao, arXiv:1601.05780.
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Interacting spin islands in a depleted strong-leg spin ladder
K. Yu. Povarov,1 D. Schmidiger,1 S. Galeski,1 N. Reynolds,1 R. Bewley,2 T. Guidi,2 J. Ollivier,3 A.
Zheludev1
1
Neutron Scattering and Magnetism, Laboratory for Solid State Physics, ETH Zurich, Switzerland
2
ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United
Kingdom
3
Institut Laue-Langevin, 6 rue Jules Horowitz, 38042 Grenoble, France0% Zn
4% Zn
Impurities, embedded in a strongly interacting medium, can often give rise to a novel emergent
objects with highly non-trivial properties. An illustrative example is a nonmagnetic impurity in a
Heisenberg S= 1/2 spin ladder. Although the ground state of the parent model is a quantumdisordered paramagnet, depletion creates extended clusters of staggered magnetization with total S
= 1/2 [1]. They can be treated as localized S = 1/2 objects, interacting with each other via the
distance-dependent Heisenberg signalternating exchange [1, 2]. Thus, introducing spinless defects
one releases a new strongly interacting spin system "on top" of the spin ladder. We experimentally
demonstrate manifestations of this physics in Zn-diluted strong-leg spin ladder (C7H10N)2CuBr4
(known as Dimpy) [3]. Magnetization measurements clearly show the presence of spinful objects
in depleted Dimpy, with interaction strength between them increasing with the zinc concentration.
High resolution time-of-ight neutron spectroscopy also allows us to probe these interactions directly.
Figure 1 compares the magnetic excitation spectra in clean and slightly depleted Dimpy, visualizing
the dynamic spin correlations stemming from nonmagnetic impurities. Absence of any variation in
these additional in-gap states in the directions, transverse to the ladder, associates them with truly
one-dimensional objects. Both static and dynamic properties of Dimpy with non-magnetic defects
are in a good agreement with the numerical calculations, based on combination of Density Matrix
Renormalization Group for large depleted ladders and the exact diagonalization methods for the
effective basis ofinteracting spin islands. This is a beautiful example of reduction of a many-body
problem to a few-body problem in a strongly correlated system through the emergent quasiparticles
concept.interacting spin islands. This is a beautiful example of reduction of a many-body problem
to a few-body problem in a strongly correlated system through the emergent quasiparticles concept.
Reference：
[1] M. Sigrist, A. Furusaki, J. Phys. Soc. Jpn. 65, 2385 (1996)
[2] A. Lavarelo, G. Roux, N. Laorencie, Phys. Rev. B 88, 134420 (2013)
[3] D. Schmidiger, P. Bouillot et al., Phys. Rev. Lett. 108, 167201 (2012)
Figure 1: Neutron spectroscopy in Zn-diluted Dimpy:
false color map of scattering intensity as a function of
momentum transfer along the ladder Q|| and energy
transfer ℏω.Left: clean (C7H10N)2CuBr4 with a welldefined excitation and no intensity in the gap. Right:
depleted (C7H10N)2Cu0.96Zn0.04Br4 with an additional
stripe of in-gap intensity in the antiferromagetic
zonecenter, coming from interacting spin islands.
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Raman Study of Spin Excitations in Quantum Spin Ladders
G Simutis1, S.Gvasaliya1, F. Xiao2, C. P. Landee3 and A. Zheludev1
1
Neutron Scattering and Magnetism Laboratory, ETH Zurich, Switzerland
2
Department of Physics, Durham University, Durham, United Kingdom
3
Department of Physics, Clark University, Worcester, MA 01610, USA
We present a Raman spectroscopy study of magnetic excitations in quantum spin
ladders. A family of organometallic compounds Cu(Qnx)(Cl1−xBrx)2 is investigated [1].
The low energy spectra are found to be dominated by scattering from two magnons.
Typical data from the end-compounds are shown in the figure below. We have
measured the whole doping series and found that the onset and the cutoff of the
scattering increases steadily as Cl is replaced by Br, suggesting that the energy scale
involved in the exchange is increasing. Moreover, as seen from the figure, the cutoff
increases more rapidly than the onset. This indicates that upon increase of Br
concentration, the exchange along the leg of the ladder is increasing faster than the
exchange along the rung. Therefore, the optical spectroscopy shows that the ratio of the
leg and rung exchange can be tuned by replacing the halogen ions. Our study is found
to be consistent with earlier predictions of tunability based on bulk measurements [2].
Figure 1: Raman spectra of the two end compounds of the Cu(Qnx)(Cl1−xBrx)2 spin
ladder family. The broad feature is due to two-magnon scattering. Shaded areas
represent scattering from the phonons.
Reference:
[1] G.Simutis et al., arXiv:1510.06360 (2015)
[2] K.Povarov et al., JMMM 370, 62 (2014)
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Exotic Phases in Frustrated Spin Chain
1
1
Aslam Parvej and 1Manoranjan Kumar
Department of Condensed Matter Physics and Material Sciences, SNBNCBS, Kolkata, India
Isotropic J1-J2 model with frustrating exchange interactions in the presence of an
axial magnetic field shows many exotic phases, such as vector chiral, spin nematic and
multipolar phases. The phase boundaries of these phases are calculated based on the
order parameters, energy level crossings and magnetization jumps in the system. At
finite magnetic field a broken symmetry states are used to calculate the order parameter
of the vector chiral phase. The exact diagonalization and the density matrix
renormalization group results are used to show that the vector chiral phase exists only
in a narrow range of J2/J1 parameter space. The energy level crossings and degeneracies
in the presence of the axial magnetic field are studied in detail using the exact
diagonalization method. In the spin nematic phase, the magnetization jumps can be
associated with the binding energy of two magnons localized at two different legs of
the zigzag chain. In this phase, magnon condensate at absolute zero temperature. The
magnetic excitation in the spin nematic phase is investigated through dynamical spin
structure factor by using dynamical density matrix renormalization group method.
Reference:
[1] A. Parvej and M. Kumar JMMM 401, 96-101 (2016)
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Magnetic Phase Diagram of Frustrated Spin Ladder
Takanori Sugimoto1, Michiyasu Mori2, Takami Tohyama1, and Sadamichi Maekawa2
1
2
Department of Applied Physics, Tokyo University of Science, Tokyo, Japan
Advanced Science Research Center, Japan Atomic Energy Agency, Ibaraki, Japan
BiCu2PO6 is a low-dimensional quantum spin system, which is attracting much
attention due to successive magnetic phase transitions [1]. The corresponding magnetic
model is regarded as a frustrated two-leg spin ladder, which bridges between the
frustrated spin chain and the non-frustrated spin ladder with 1/2 spins [2]. The
preceding study on this model has presented that magnetization plateaux emerge at 1/2,
2/3, and 1/3 magnetizations, in addition to cusp singularities. To discuss whether the
magnetization plateau can appear in the real compound BiCu2PO6 or not, the magnetic
phase diagram should be clarified.The preceding study on the magnetization plateaux
shows that the quasi-spin picture is important to understand the mechanism of plateau
[2]. In this picture, two 1/2 spins on a rung with certain applied magnetic fields are
redefined as a quasi 1/2 spin, whose up and down spin states correspond to a triplet and
the singlet states, respectively. The original spin-ladder model can be mapped onto
another quasi-spin chain model with an effective magnetic field, and an anisotropy.
We investigate the correlation functions of the quasi-spins with the density-matrix
renormalization-group method, and discover the long-ranged order of the quasi-spin
dimer operator in the 1/2 plateau. The quasi-spin dimer operator is used to determine
the phase boundary of the 1/2 plateau.
In addition, we calculate the gap function at 1/2, 1/3, and 2/3 magnetizations, to
clarify the phase boundaries or to compare the phase boundary with that obtained by
the quasi-spin dimer operator. We find that the boundaries determined by the gap
function is identical to those obtained in the limit of the strong rung couplings. The
result is consistent with the preceding work.
The gap function at the 1/2 magnetization depends on not only the frustration but
also the intrinsic anisotropy, which has been claimed by A. A. Tsirlin [3] and K. W.
Plumb [4]. Therefore, a question whether the 1/2 plateau appears or not in BiCu2PO6,
will give important information associated with the anisotropy.
Reference:
[1] Y. Kohama, et al., Phys. Rev. Lett. 109, 167204 (2012).
[2] T. Sugimoto, M. Mori, T. Tohyama, and S. Maekawa, Phys. Rev. B 92, 125114
(2015); Physics Procedia 75, 861 (2015).
[3] A. A. Tsirlin, et al., Phys. Rev. B 82, 144426 (2010).
[4]K. W. Plumb, et al., Nat. Phys. AOP, 3566 (2015).
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Dependence of the coupled spin and orbital dynamics on doped
magnetic impurities in a cuprate spin chain
M. Dantz1, J. Pelliciari1, K. Karmakar2, Y. Huang1, V, Strocov1, S. Singh2 and T. Schmitt1
1
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland,
2
Indian Institute of Science Education and Research, PuneAuthor
Email: [email protected]
Low dimensional magnetism has been intensively studied over the last 80 years as
a unique playground for theories for higher dimensional magnetism. The one
dimensional Heisenberg S=1/2 antiferromagnetic (AFM) spin chain has received
particularly much attention in both theory and experiments [1,2,3]. One of the best
realizations of this model is the one-dimensional cuprate Sr2CuO3, in which cornershared copper-oxygen plaquettes form 1D AFM chains. For this system it has recently
been shown that even very small defect doping has dramatic effects on macroscopic
properties [4,5]. It is therefore desirable to access the elementary excitations up to
several eV in this system in order to unravel the nature of these doping effects.
We employed high resolution Resonant Inelastic X-Ray Scattering (RIXS) in order
to access the elementary excitations and their interplay in Sr(2-x)TMxCuO3 (TM=Co, Ni,
Zn) where Co, Ni and Zn represent spin ½, 1 and 0 defects, respectively. We show that
this defect doping strongly influences the microscopic magnetism i.e. the 2+4 spinon
continuum of the elementary magnetic excitations of the 1D antiferrmagnetic
Heisenberg chain. We find a significant hardening of up to 50 meV of the spinon
continuum for all dopants, revealing a strong correlation of the effective superexchange
parameter J with doping. While the hardening occurs for all dopants, we find the
hardening to be the strongest upon Zn doping, followed by Ni and Co. This trend bears
a striking resemblance to the electron-doping dependence of the paramagnon
excitations in two-dimensional cuprate superconductors. [6,7]
Reference:
[1] Schlappa et al. Nature 485, 82-85, (2012)
[2] Schlappa et al. PRL 103, 047401, (2009)
[3] Klauser et al. PRL 105, 157205, (2011)
[4] Simurtis et al. PRL 111, 067204 (2013)
[5] Sirker et al. PRL 98, 137205 (2007)
[6] Wohlfeld et al. Nat. Comm 5:3314 (2014)
[7] Lee et al. Nat Phys. 10, 883–889 (2014)
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Energy and Spindynamics of Quantum Magnets: a Typicality View
Robin Steinigeweg1,2, Wolfram Brenig1, Jochen Gemmer2, Jacek Herbrych3, and Xenophon Zotos3
1
Institute for Theoretical Physics, Technical University Braunschweig, Germany
2
Department of Physics, University of Osnabrück, Ger many
3
Department of Physics, University of Crete, Heraklion, Greece
We provide insights which emerge from the new concept of quantum typical purestate propagation as applied to the real-time dynamics of spin- and energy currents in
quasi one-dimensional spin chain and ladder systems at finite temperature. It will be
shown, that typicality is satisfied over a substantial range of temperatures, is fulfilled
both, in integrable and nonintegrable systems, and significantly improves existing
results from exact diagonalization, Lanczos, and time-dependent density matrix
renormalization group. For the integrable case, the long-time dynamics of the spin
currents and the spin Drude weight will be extracted beyond previously accessible
combinations of system sizes and time domains. Strong evidence will be provided for
the high-temperature Drude weight to vanishes at the isotropic point. For the
nonintegrable cases, chains in staggered fields and spin ladders will be considered. We
will discuss the relaxation curve of the energy current and determine the heat
conductivity as a function of magnetic field, exchange anisotropy, and temperature. For
the spin ladder a comprehensive picture of the thermal conductivity over the entire
range from weak to strong rung coupling will be provided.
Reference:
[1] Robin Steinigeweg, Jacek Herbrych, Xenophon Zotos, and Wolfram Brenig,
Phys. Rev. Lett. 116, 017202 (2016)
[2] Robin Steinigeweg, Jochen Gemmer, and Wolfram
Brenig, Phys. Rev. B 91, 104404 (2015).
[3] Robin Steinigeweg, Jochen Gemmer, and Wolfram Brenig,
Phys. Rev. Lett. 112, 120601 (2014).
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Inelastic Neutron Scattering Study of Sr2CuWO6 – a double
perovskite at the border between two and three dimensional
magnetism
H. C. Walker1, O. Mustonen2, S. Vasala2,3, D. T. Adroja1,4, M. Karppinen 2
1ISIS Neutron and Muon Facility, Rutherford Appleton Laboratory, Oxfordshire, UK
2
Aalto University, Aalto, Finland
Laboratory of Photonics and Interfaces, École Polytechnique Fédérale de Lausanne, CH-1015
Lausanne, Switzerland
4
Highly Correlated Matter Research Group, Physics Department, University of Johannesburg,
P.O. Box 524, Auckland Park 2006, South Africa
3
Sr2CuWO6 is a double perovskite at the border between two and three dimensional
magnetism, with a square lattice of S=1/2 CuII ions. This makes it an interesting
analogue for the antiferromagnetic parent phases of the high Tc superconductors, but
with weaker in-plane superexchange, making it possible to study the low temperature
low dimensional magnetic properties. Exchange constants had been calculated using
DFT [1], and we have explored these experimentally by measuring the thermal
evolution of the spin waves using inelastic neutron scattering, and comparing it to
simulations calculated using linear spin wave theory via the SpinW program [2]. This
reveals that the theoretically estimated parameters account for the observed spin wave
scattering very well. Our analysis confirms that not the nearest neighbour, but the next
nearest neighbour interactions in the basal plane are the strongest.
Reference:
[1] S. Vasala et al., PRB 89, 134419 (2014)
[2] S. Toth and B. Lake, JPCM 27, 166002 (2015)
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Magnetization studies of the La1.5Ca0.5CoIrO6 reentrant spin glass
system
L.T. Coutrim,1E. M. Bittar,2 F. Stavale,2 F. Garcia,2 E. Baggio-Saitovitch,2
M. Abbate,3 R. J. O. Mossanek,3 H. P. Martins,3 D. Tobia,4 P. G. Pagliuso,4 and L. Bufaiçal1
1
2
Federal University of Goiás (UFG), Goiânia, GO, Brazil
Brazilian Center for Research in Physics (CBPF), Rio de Janeiro, RJ, Brazil
3
Federal University of Paraná(UFPR), Curitiba, PR, Brazil
4
State University of Campinas (UNICAMP), Campinas, SP, Brazil
We report magnetization studies of the unusual magnetic properties in the
La1.5Ca0.5CoIrO6 double perovskite compound. A reentrant spin glass-like state on an
antiferromagnetic matrix was observed via ac magnetic susceptibility, where the
frequency dependence of freezing temperature satisfies the power law of the dynamical
scaling theory. In addition, dc magnetic measurements showed up to three
compensation temperatures of its magnetization, for an appropriate choice of the
applied magnetic field. A strong anisotropy, with spontaneous exchange bias effect,
due to different competing magnetic interactions, was seen in field dependent
magnetization curves. We discuss our results in terms of magnetic phase separation and
magnetic frustration of Ir moments, caused by the competing interactions with its
neighboring Co ions.
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Random transverse fields on spin ice in Pr2Zr2O7
J.-J. Wen1,*, S. M. Koohpayeh1, K. A. Ross1,2, B. A. Trump 3, T. M. McQueen1,3,4, K.Kimura5,
S. Nakatsuji5, Y. Qiu2,6, D. M. Pajerowski2, J. R. D. Copley2, C. L. Broholm1,2,4
1
Institute for Quantum Matter and Department of Physics and Astronomy, The Johns
Hopkins University, Baltimore, MD, USA
2
NIST Center for Neutron Research, National Institute of Standards and Technology,
Gaithersburg, MD, USA
3
Department of Chemistry, The Johns Hopkins University, Baltimore, MD, USA
4
Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore,
MD, USA
5
Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba, Japan
6
Department of Materials Science and Engineering, University of Maryland, College Park, MD,
USA
Despite the rare earth pyrochlore material Pr2Zr2O7 exhibit many characteristics of
classical spin ice, it remains highly dynamical at low temperatures, which is in strong
contrast with the classical counterpart. Here we show the existence of inhomogeneous
level splitting of non-Kramers Pr3+ ground state doublet in stoichiometric single crystals
of Pr2Zr2O7, which enhances quantum spin dynamics. Inelastic neutron scattering
reveals a continuum of excitations at all accessed wave vectors, the temperature and
magnetic field dependence of which indicate a continuous distribution of quenched
transverse fields on the Pr3+ non-Kramers doublet. Random phase approximation
calculations of the response function for a nearest neighbor spin ice model with a
random transverse field provide an excellent description of the data. The quenched
random fields indicate an incommensurate or large unit cell structure for stoichiometric
Pr2Zr2O7 that breaks three-fold rotational symmetry at rare earth sites.
*
Present address: Department of Applied Physics, Stanford University, Stanford, CA,
USA
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A spin-orbit coupled triangular lattice quantum spin liquid in
YbMgGaO4: a semiclassical study
Yao-Dong Li1, Gang Chen2,3,4
1School of Computer Science, Fudan University, Shanghai, China
2 Department of Physics, State Key Laboratory of Surface Physics, Fudan University,
Shanghai, China
3Perimeter Institute for Theoretical Physics, Waterloo, Canada
4Collaborative Innovative Center for Advanced Microstructures, Fudan University,
Shanghai, China
Recently YbMgGaO4 is proposed to be the first strong spin-orbit coupled quantum
spin liquid candidate system that contains odd number of electron per unit cell with
effective spin-1/2 local moments. In this talk we analyze the classical phase diagram of
the most generic model that describes the Yb effective spin-1/2 local moments on the
triangular lattice. We show the frustration is strong near the phase boundary between
the 120-degree state and the stripe ordered phase. Further, we study the quantum
fluctuation of the spin momentum by the linear spin wave theory and find that the
magnetic order is destroyed in the strongly frustrated regimes of the phase diagram.
Our result is compatible with the experimental results that suggest a quantum spin liquid
ground state.
Reference:
[1] Y.-D. Li and G. Chen, arxiv: 1512.02151.
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Magnetic field induced long range order in the novel spin-liquidlike pyrochlore Y2CrSbO7
L. Shen 1, E. Blackburn 1, R. Riyat 1, T. C. Hansen 2, C. Greaves 3
1,
School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, United
Kingdom
2,
Institut Laue-Langevin, B.P. 156, 38042 Grenoble Cedex 9, France
3,
School of Chemistry, University of Birmingham, Birmingham, B15 2TT, United Kingdom
The current search for classic spin- liquid states (S ≠½) is mainly focused among
systems adopting both geometrical frustration and antiferromagnetic exchange
interactions. The role of quenched disorder, which may lead to zero point spin exchange
fluctuations (ZPSEFs) when it becomes critical, is rarely discussed. Diluted metalyttrium oxides Y2M2-xNxO7 (M = magnetic cation, N = nonmagnetic cation) are ideal
systems to study the magnetic percolation phenomenon in pyrochlores where the
threshold is predicted to be xc ≈ 1.22. We follow the evolution of magnetism in Y2Cr1yGaySbO7 (0 ≤ y ≤ 0.8) as a function of temperature, magnetic field and doping level
by means of magnetic susceptibility measurements and high resolution neutron
diffraction. In zero field, while the end compound Y2Mn2O7 (x = 0, Mn4+/ 3d3)
undergoes a magnetic transition at 16 K 1, the intermediate Y2CrSbO7 (x = 1.0 < xc,
Cr3+/ 3d3) does not show any magnetic order down to 1.8 K. On the other hand, a
ferromagnetic-like transition is observed around TC = 12.5 K in Y2CrSbO7 and
Y2Cr0.8Ga0.2SbO7 (x = 1.2) when µ0H = 5 T. By further increasing the Ga-doping level,
this transition abruptly drops down to 5.5 K in agreement with the value extracted from
the Brillouin function for a ‘polarised paramagnet’, therefore validating the percolation
model. In Y2CrSbO7, the cation size mismatch between Cr3+ and Sb5+ and their random
occupation on 16d sites triggers the quenched disorder. Most of all, the critical Cr3+O2--Cr3+ bond angle necessary for realizing zero point fluctuations is confirmed by our
Rietveld refinement 2.
In this talk, the experimental results mentioned above will be discussed in the
framework of ZPSEFs. We will also try to provide possible solutions for the field
induced magnetic structure in Y2CrSbO7. Finally, we correct the previous model used
for percolation simulation by introducing quenched disorder. Based on this new model,
the zero field magnetic percolation threshold of Y2M2-xNxO7 will be predicted.
Reference:
[1] Y. Shimakawa, et al. Physical Review B, 59, 1249 (1999)
[2] K. Motida, et al. Journal of the Physical Society of Japan, 28, 1188 (1970)
163
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High-pressure synthesis and characterizations of the R2Pt2O7
pyrochlores
Y. Q. Cai1, Q. Cui1, X. Li2, Z. L. Dun3, J. Ma3, C. dela Cruz4, Y. Y. Jiao1, J. Liao1,
P. J. Sun1, Y. Q. Li1, J. S. Zhou2, J. B. Goodenough2, H. D. Zhou3, and J.-G. Cheng1*
1
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics,Chinese
2
Materials Science and Engineering Program and Texas Materials Institute, University of Texas
at Austin, Austin, TX 78712, USA
3
Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA
4
Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831,
USA
*[email protected]
Pyrochlore oxides R2B2O7 where R3+ stands for rear-earth ion and B4+ for a
nonmagnetic cation such as Sn4+or Ti4+consist of an important family of geometrically
frustrated magnets, which have been the focus of extensive investigations over last
decades.[1] To further enlarge the R2B2O7 pyrochlores, we have chosen to stabilize the
Pt-based cubic pyrochlores under HPHT conditions [2] for two reasons: (1) Pt4+ is in a
low-spin state which ionic radius is located in between Ti4+ (0.605 Å) and Sn4+ (0.69
Å), and (2) Pt4+ has a spatially much more extended 5d orbitals and thus enhanced Pt
5d-O 2p hybridizations that might modify the local anisotropic exchange interactions.
Such an effect has never been taken into account in the previous studies. In this work,
we will present the detailed characterizations on the cubic pyrochlores R2Pt2O7 obtained
under HPHT conditions [3].
References
[1] J. S. Gardner, M. J. P. Gingras, and J. E. Greedan, Rev. Mod. Phys. 82, 53 (2010).
[2] H. R. Hoekstra and F. Gallagher, Inorg. Chem. 7, 2553 (1968).
[3]Y. Q. Cai, et al. PRB (2016) in press.
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Magneto-optical absorption of the pyrochlore compounds Re2T2O7
(Re: Dy, Tb, Pr; T: Ti, Zr).
Kun Zhang1, Cheng Chen1, Yibo Han1,*, Junbo Han1, Junfeng Wang1, and Liang Li1
1Wuhan National High Magnetic Field Center and school of physics, Huazhong University
of Science and Technology, Luoyu road 1037, Wuhan 430072, China
Three kinds of single crystal Dy2Ti2O7, Pr2Zr2O7, Tb2Ti2O7 with pyrochlore structure
were investigated by the magneto-optical absorption measurements. The absorption spectra
in the visible and near infrared region were taken at different temperatures and magnetic
fields along the [111] crystal axis. The absorption peaks corresponding to the oxygen
vacancy become narrowing and redshift with decreasing temperature. By applying a pulsed
high magnetic field, the absorption peaks of Dy2Ti2O7 crystal redshift, while other two
crystals almost do not change with the increasing field at the lowest temperature. The effect
of oxygen vacancy on the absorption spectra in the visible region of those three crystals
was investigated by the first-principles calculation based on the density functional theory.
Absorption peak in the near infrared are caused by phonon mode. It is found enhanced
charge localization result in the spectra linewidth narrowing and the spin-phonon coupling
induces the redshift.
Reference:
[1] C Z Bi et al, J. Phys.: Condens. Matter 17 (2005) 5225-5233.
[2] Junbiao Kang et al, J. Alloy. Compd. 599 (2014) 170-174.
165
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Spin Ice Physics in the New Spinel Material CdEr2Se4
Shang Gao1,2, Oksana Zaharko1, Tom Fennell1, Vladimir Tsurkan3,4, Bjorn Fåk5, Andrew
Wildes5,Antonio Cervellino6, Christian Rüegg1,2
1
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, Villigen, Switzerland
2
Department of Quantum Matter Physics, University of Geneva, Geneva, Switzerland
3
Experiemental Physics V, University of Augsburg, Augsburg, Germany
4
Institute of Applied Physics, Academy of Sciences of Moldova, Chisnau, Moldova
5
Institut Laue-Langevin, Grenoble, France
6
Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland
The formation of spin ice is a well-established phenomenon in pyrochlore oxides like
Ho2 Ti2O7 and Dy2Ti2O7. In these compounds, the crystal field constrains the spins to
point 'in' or 'out' of the tetrahedron along the local <111> cubic axis and the dominant
dipolar interaction imposes a strong 'two-in-two- out' ice rule. Such a state possesses
excitations of emergent magnetic monopoles and further study calls for identification
of new classes spin ice compounds. Recently, the spinel material CdEr2Se4 was
proposed to be the first spin ice outside the rare earth pyrochlore oxide paradigm [1].
In this compound, the Er3+ ions occupy the spinel B sites and form a corner-sharing
network of tetrahedra, as in the rare-earth titanate pyrochlores. Specific heat
measurements verified the zero-point entropy of (R/2)ln(3/2), and magnetization
measurements demonstrated the Ising spin symmetry [1]. Here we present microscopic
proofs for this new spin ice state based on neutron scattering experiments. Inelastic
neutron scattering experiments are performed on the IN4 and IN6 time-of-flight
spectrometers at ILL, Grenoble. The crystal electric-field parameters and the wave
functions for the ground state are determined. A strong Ising character of the ground
state is identified, and the energy gap for the first excited state is relatively high (3.96
meV). This ensures the validity of the Ising model, which is a prerequisite for the spin
ice state. Diffuse neutron scattering experiments are performed on D7 and D20 at ILL,
Grenoble. Below 25 K, strong diffuse scattering starts to build up and finally leads to
two broad peaks centered around 0.6 and 1.4 Å -1 at 0.1 K. Monte Carlo simulations for
the dipolar spin ice model [2] are used to fit the pattern and the dominance of the
ferromagnetic dipolar interactions is confirmed. As a conclusion, our crystal field study
confirms the Ising character of the Er3+ spin and diffuse scattering data proves the
dominance of dipolar interactions in CdEr 2Se4. In this way, we establish the first
microscopic evidences that CdEr2Se4 is a novel spin ice.
Reference:
[1] J. Lago et al., Phys. Rev. Lett. 104, 247203 (2010)
[2] B. C. den Hertog et al., Phys. Rev. Lett. 84, 3430 (2000)
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Correlated impurities and intrinsic spin liquid physics in the kagome
material Herbertsmithite
Tian-Heng Han1,2, M. R. Norman1, J.-J. Wen3,4, Jose A. Rodriguez-Rivera5,6, Joel S. Helton5,7,
Collin Broholm5,8, Young S. Lee3,4
1
Materials Science Division, Argonne National Laboratory, Argonne, IL, USA
James Franck Institute and Department of Physics, University of Chicago, Chicago, IL, USA
3
Department of Applied Physics, Stanford University, Stanford, CA, USA
4
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory,
Menlo Park, CA, USA
5
NIST Center for Neutron Research, National Institute of Standards and Technology,
Gaithersburg, MD, USA
6
Department of Materials Science, University of Maryland, College Park, MD, USA
7
Department of Physics, The United States Naval Academy, Annapolis, MD, USA
8
Institute for Quantum Mater and Department of Physics and Astronomy, The Johns Hopkins
University, Baltimore, MD, USA
2
The possible realization of quantum spin liquid in the kagome material
ZnCu3(OH)6Cl2(Herbertsmithite) represents a breakthrough in the search for
quantum spin liquids. Despite a sizable nearest neighbor superexchange interation of ~
200 K, herbertsmithite does not order nor freeze magnetically down to at least 0.05 K.
Recent inelastic neutron scattering measurements revealed a continuum of scattering
indicating fractionalized magnetic excitations, which further pointed to a quantum spin
liquid state in this material.The probing of the nature of the putative spin liquid state,
in particular the existence of a spin gap or not, however, is complicated by the existence
of weakly interacting impurity spins that occupy ~15% of the Zn sites in between the
kagome layers. Through extensive high resolution inelastic neutron scattering
measurement probing both the in plane and out of plane inter-spin correlations, here we
show that the lower energy (E < 0.8 meV)magnetic scattering is due to impurity spins,
while the higher energy scattering arises from spins in the kagome layers. An impurity
spin is found to be mainly antiferromagnetically correlated to another nearest neighbor
impurity spin in adjacent Zn layers, while the correlations between the impurity spins
and that on the kagome layers are insignificant. Our findings suggest the kagome layer
spins in herbertsmithite realize a gapped quantum spin liquid state with a gap size of ~
0.7 meV, consistent with recent NMR measurements.
167
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Non-Abelian Chiral Spin Liquid on the Kagome lattice
Zheng-Xin Liu1, Hong-Hao Tu2, Ying-Hai Wu2, Rong-Qiang He3, Xiong-Jun Liu4, Yi Zhou5, TaiKai Ng6
1
Department of Physics, Renmin University of China, Beijing, China
Max-Planck-Institut fu ̈r Quantenoptik, Hans-Kopfermann-Str. 1, D-85748 Garching, Germany
3
Institute for Advanced Study, Tsinghua University, Beijing, China
4
International Center for Quantum Materials and School of Physics, Peking University, Beijing
100871, China
5
6
Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay
Road, Kowloon, Hong Kong
2
We study S=1 spin liquid states on the Kagome lattice constructed by Gutzwiller
projected p+ip superconductors. Depending on the topology of the fermions, the
obtained spin liquids can be either non-Abelian or Abelian. By calculating the modular
matrices S and T, we confirm that projected topological superconductors are nonAbelian chiral spin liquid (NACSL). The chiral central charge and the spin Hall
conductance we obtained agrees very well with the SO(3)1 field theory predictions.
The NACSL may be stabilized by a local Hamiltonian. We illustrate that the NonAbelian anyons may be localized (which is necessary for possible applications in
quantum computation) by defect three-body interactions. From a variational study we
observe a topological phase transition from the NACSL to a Z2 Abelian spin liquid.
Reference:
[1] Zheng-Xin Liu et al., arXiv: 1509.00391
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Topological defects in quantum spin-nematics
Yutaka Akagi1, Hiroaki T. Ueda2, Nic Shannon3
1
Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo, Japan
2
Faculty of Engineering, Toyama Prefectural University, Toyama, Japan
3
Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan
Topological defects play an important role in both conventional liquid crystals, and
in the theory of two-dimensional quantum spin liquids [1]. However, relatively little is
known about their role in quantum spin nematic phases which have no long-range
dipole order and break only spin-rotational symmetry [2-5]. Here, we consider the
topological defects in these nontrivial states. The model is the spin-1 bilinear
biquadratic model on the triangular lattice [6-8]. Using homotopy analysis and
numerical optimization approach, simulated annealing, we identify a new family of
solitons at a particular point in parameter space, in which the system has global SU(3)
symmetry. We also find that wave functions with higher topological charges
spontaneously decay into “elementary” solitons with emergent interactions. This result
suggests that it could be possible to realize a new class of interacting soliton in
experiments on cold atoms, as well as the possibility of new form of quantum spin
liquid [9,10].
Reference:
[1] A. V. Chubukov, S. Sachdev, and T. Senthil, Nucl. Phys. B 426 [FS], 601 (1994).
[2] B. A. Ivanov, R. S. Khymyn, and A. K. Kolezhuk, Phys. Rev. Lett. 100, 047203
(2008).
[3] T. Grover and T. Senthil, Phys. Rev. Lett. 107, 077203 (2011).
[4] J. Takano and H. Tsunetsugu, J. Phys. Soc. Jpn. 80, 094707 (2011).
[5] C. Xu and A. W. W. Ludwig, Phys. Rev. Lett, 108, 047202 (2012).
[6] A. Lauchil, F. Mila, and K. Penc, Phys. Rev. Lett. 97, 087205 (2006).
[7] H. Tsunetsugu and M. Arikawa, J. Phys. Soc. Jpn. 75, 083701 (2006).
[8] A. Smerald and N. Shannon, Phys. Rev. B 88, 184430 (2013).
[9] H. T. Ueda, Y. Akagi, and N. Shannon, accepted for publication in Phys. Rev. A
(arXiv:1511.06515).
[10] Y. Akagi, H. T. Ueda, and N. Shannon, in preparation.
169
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Low-energy electrodynamic of quantum spin liquid candidate
YbMgGaO4
1
1
1
T.Dong , H.P.Wang , L.Y.Shi , Y.S.Li2, Q.M.Zhang2, N.L.Wang1,3
1
International Center for Quantum Materials, School of Physics, Peking University, China
2
Department of Physics, Renmin University of China, China
3
We report a direct measurement of the low-energy optical conductivity of large-area
single crystal YbMgGaO4, a newly found spin-liquid candidate material, by means of
time domain terahertz spectroscopy. No magnetic resonance absorption was observed
in polarization dependent measurement down to 1.5K, indicating absence of magnetic
order. From magneto-terahertz measurement up to 7T within Faraday geometry, we
observe an absorption feature which is linearly proportional to the applied magnetic
field, yielding evidence for a Zeeman splitting of effective spin 1/2 energy level, from
which we extract the value of in-plane g-factors 𝑔|| ~4.2. Furthermore, we measure
reflectivity and transmittance spectra between 10000𝑐𝑚−1 and 20000𝑐𝑚−1 using FTIR,
our measurement reveal that the fine structure spectrum of YbMgGaO4 is similar to a
single ion 𝑌𝑏 3+ absorption features arising from ground state 2𝐹7/2 to
2
𝐹5/2 excitations in trigonal crystal electric field. From optical measurement, we
suggest that YbMgGaO4 is a nonmagnetic insulator and long range order do not develop
down to 1.5K.
170
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Vortex Crystals with Chiral Stripes in Itinerant Magnets
R. Ozawa1, S. Hayami2, K. Barros2, G.-W. Chern3, Y. Motome1, and C. D. Batista2
1
Department of Applied Physics, The University of Tokyo, Tokyo, Japan
2
Los Alamos National Labratory, NM, USA
3
Department of Physics, The University of Virginia, VA, USA
Noncoplanar spin configurations in itinerant magnets have been attracting much
interest because they act as a huge effective magnetic field for itinerant electrons
through the spin Berry phase mechanism and bring about peculiar quantum transport
phenomena. Chiral magnets with the spin-orbit coupling (SOC) are good platforms of
stabilizing noncoplanar spin configurations, such as skyrmion crystals. Recently,
several noncoplanar spin configurations induced by Fermi surface instabilities have
been discovered in itinerant magnets for certain electron filling fractions even in the
absence of the SOC [1-6]. Here, we demonstrate that noncoplanar ordering is a generic
property of a class of frustrated itinerant magnets in their weak-coupling limit and
unveil the origin of the muti-modulated structures induced by Fermi surface instabilites.
By performing large-scale Langevin dynamics simulations [7] of the square Kondo
lattice model, we find double-Q noncoplanar vortex-antivortex crystals [8] (see Figure).
We study the stabilization mechanism by complementary approaches: (1) perturbative
expansion with respect to the spin-charge coupling and degree of noncoplanarity, (2)
direct diagonalization of the full Hamiltonian, and (3) truncation of the spin scattering
processes in higher harmonics. All these studies consistently clarify the origin of the
double-Q vortex crystals. Our results indicate that the key ingredient is “frustration”
arising from multiple peaks of the bare magnetic susceptibility, which is a generic
property of high-symmetry itinerant helimagnets.
References:
[1] I. Martin and C. D. Batista, Phys. Rev. Lett. 101, 156402 (2008)
[2] Y. Akagi and Y. Motome, J. Phys. Soc. Jpn. 79, 083711 (2010)
[3] G.-W. Chern, Phys. Rev. Lett. 105, 226403 (2010)
[4] J. W. F. Venderbos et al., Phys. Rev. Lett. 109, 166405 (2012)
[5] K. Barros et al., Phys. Rev. B 90, 245119 (2014)
[6] S. Hayami and Y. Motome, Phys. Rev. B 90, 060402(R) (2014)
[7] K. Barros and Y. Kato, Phys. Rev. B 88, 235101 (2013)
[8] R. Ozawa et al., preprint (arXiv:1510.06830)
Fig. Schematic picture of a noncoplanar vortex crystal. Arrows are the in-plane spin components and the
solid (dashed) circle indicates a vortex (antivortex). The striped modulation of the spin scalar chirality,
a measure of noncoplanarity, is shown in the background (gray-scale contour plot).
171
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Spin wave approach to the two-magnon Raman scattering in an J1xJ1y-J2-Jc antiferromagnetic Heisenberg model
Changle Liu1, Xiaoqun Wang1,2, Rong Yu1, 2
1Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials
& Micro-nano Devices, Renmin University of China, Beijing 100872, China
2 Department of Physics and Astronomy, Collaborative Innovation Center of
Advanced Microstructures, Shanghai Jiaotong University, Shanghai 200240, China
We study the two-magnon non-resonant Raman scattering in the (π, π) and (π, 0)
ordered antiferromagnetic phases of a J1x-J1y-J2-Jc Heisenberg model on the tetragonal
lattice within the framework of the spin-wave theory. We discuss the effects of various
tuning factors to the two-magnon Raman spectra. We find that both the magnetic
frustration J2/J1 and the interlayer exchange coupling Jc may significantly affect the
spectra in both the B1g and A1g channels in the (π, π) Néel ordered phase. Moreover,
we find a splitting of the two-magnon peak in the (π, 0) antiferromagnetic phase. We
further discuss the implications of our results to the BaMnBi2 and iron pnictide systems.
Reference:
[1] C. Liu, X. Wang and Y. Rong, arXiv:1510.03359 (2015).
[2] C. Luo, T. Datta, and D.-X. Yao, PRB 89, 165103 (2014).
[3] T. Nagao and J. Igarashi, PRB 75, 214414 (2007).
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Random Field Ising versus Bose Glass Physics in a disordered
Quantum Magnet
G. Perren1, W. E. A. Lorenz1, E. Ressouche2, A. Zheludev1
1
Neutron Scattering and Magnetism, Laboratory for Solid State Physics, ETH Zurich, CH-8093
Zurich, Switzerland
2SPSMS, UMR-E CEA/UJF-Grenoble 1, INAC, F-38054 Grenoble, France
IPA-CuCl3 is a well-known S = 1/2 gapped quantum paramagnet which exhibits a
field-induced BEC-like quantum phase transition to a magnetically ordered phase [1].
The corresponding transition in the random-bond Br-substituted derivative IPACu(ClxBr1-x)3 has been interpreted as that from a magnetic Bose Glass (BG) phase to
a what appeared to be a short range ordered state [2]. The underlying mechanism
remained unclear. In the present work we report new neutron diffraction and
calorimetric measurements on the x=5% compound. We show that Ising-type
anisotropy is a key factor, and that critical behavior and the short range order at high
field are strongly dependent on the applied field direction. The field-induced transition
in the disordered system is actually of the Ising-model-in-random-field universality
class, rather than a Bose-Glass to BEC transition.
Reference:
[1]T. Masuda et al., PRL 96, 047210 (2005)
[2]T. Hong et al., PRB 81, 060410 (2010)
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An implementation of the spin-polarized state with M=0 -the
necessary and sufficient condition
Serge N. Zagoulaev*
Department of Theoretical Physics, V.A.Fock Institute of Physics, St.Petersburg State
University,198504, Stariy Peterhof, Ulianovskaia 1, St.Petersburg, RUSSIA
* email:
[email protected]
The spin structure of the k-order reduced density matrix (RDM-k) is examined for an arbitrary
state of a N-electron system with the zero z-projection of the total spin (M = 0). It is known [1-4]
that if the state considered is the definite multiplicity state then the RDM-1
𝛼 ,𝛼
𝛽 ,𝛽
ρ0 (𝑥1 |𝑥1, ) = ρ0 1 1 (𝑟1 |𝑟1, )α(𝜎1 )α(𝜎1, ) + ρ0 1 1 (𝑟1 |𝑟1, )β(𝜎1 )β(𝜎1, )
𝛼 ,𝛼
𝛽 ,𝛽
satisfies the condition: ρ0 1 1 (𝑟1 |𝑟1, )= ρ0 1 1 (𝑟1 |𝑟1, ), for all values of 𝑟1 𝑎𝑛𝑑 𝑟1, .
In the present paper this result is generalized to the RDM-k ρ0 (𝑥1 , … , 𝑥𝑘 |𝑥1, , … , 𝑥𝑘, ), where x j≡
(r j,σ𝑗 ):
𝛼 ,𝛽 𝛽 ….𝛼 ,𝛽 𝛼 𝛽 …𝛼
𝛽 ,𝛼 𝛼 ….𝛽 ,𝛼 𝛽 𝛼 …𝛼
ρ0 1 2 3 𝑘 1 2 3 𝑘 (𝑟1 , … , 𝑟1 |𝑟1., … , 𝑟𝑘, )= ρ0 1 2 3 𝑘 1 2 3 𝑘 (𝑟1 , … , 𝑟𝑘 |𝑟1., … , 𝑟𝑘, ) (1)
Moreover, the result (1) is valid not only for the definite multiplicity states ΨS0(x1,..., xN) with M
= 0 but also for any linear combination Ψ0 = ∑S DSΨS0 of such states if all spins S in the linear
combination have the same parity. The proof is based on the fact that for any N-electron pure spin
state with M = 0 the wave function Ψ S0 acquires the factor (−1)N/2−S if all one electron spin
functions α(σ) will be changed for β (σ) and vice versa. In the developed proof, the Hamiltonian
was not used at all and it was not even assumed that the wave function ΨS0 is an eigenfunction of
some Hamiltonian. Therefore equation (1) is quite general and valid for the stationary and nonstationary states, ground and excited states, with and without homogeneous magnetic field imposed,
exact and approximate wave functions. The many electron states are known as a spin-polarized
states ρ α(r) ≠ ρ β (r) if the corresponding density of electrons ρ σ(r) ≡ ρ σ,σ(r|r) with ”spin up”
(σ = α) does not equal to that with ”spin down” (σ = β ). From (1) it follows that the necessary
and sufficient condition for the stationary state with M = 0 to be a spin-polarized is the requirement
for the Hamiltonian to mix a states with different parity spins.
The antiferromagnetic (AF) state as a particular form of the spin-polarized state with M = 0 is
discussed. Namely, the AF states obtained in several methods based on the isotropic Hamiltonian
̂ (r1,..., rN) (for example LAPW, DFT, etc), are probably due to the approximations used in these
H
methods. Approximate calculation of the Hamilton operator matrix elements, or approximate
diagonalization of the matrix can effectively transforms the initial Hamiltonian inserting the terms
which mix total spins of different parity. Because the exact initial operator can not contain the spinpolarized states with M = 0 in its spectrum. For example, among different versions of the HartreeFock (HF) method neither the conventional one-determinant spin-restricted method, nor the
conventional manydeterminant spin-extended method can result in the spin-polarized solutions with
M = 0. In this methods, the solutions correspond to the definite total spin and therefore they cannot
describe the antiferromagnetic state. Only another branch of HF methods, different spins for
different orbitals, or more general, spin unrestricted HF method can describe the AF state with M =
0.
This work was supported by RFBR (grant No 15-03-07543).
Reference:
[1] Fock V.A., Zh. Eksp. Teor. Fiz., 10, 961, (1940); [English translation: JETP, 10, (1940)].
[2] McWeeny R., Mizuno Y., Proc. Roy. Soc. A, 259, 554, (1961).
[3] Davidson E.R., ”Reduced density matrix in quantum chemistry”, Academic Press, (1976).
[4] Abarenkov I.V., Zagoulaev S.N., Int. J. Quantum Chem., 108, p.2657, (2008).
174
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Enhanced conductivity and metal-insulator transitions of ultrathin
CaRuO3 films in superlattices
Haoran Xu1, Wenbin Wu1, 2
1
2
Hefei National Laboratory for Physical Sciences at Microscale, University of Science and
Technology of China, Hefei 230026, People’s Republic of China
High Magnetic Field Laboratory, Chinese Academy of Science (CAS), Hefei 230071, People’s
Republic of China
High quality superlattices containing SmFeO3 (SFO, insulator) and CaRuO3 (CRO,
conductor) with thicknesses as small as 0.8 nm were fabricated. We studied the
enhanced conductivity and metal-insulator transitions (MITs) of ultrathin CRO films in
(SFO/CRO) x superlattices. For x=16, All superlattices with the thickness of CRO (t
CRO) more than 0.8 nm are metallic, whereas a 2.4 nm single film is insulating. Even for
x=2, with t CRO = 1.2 nm the sample is still conductive. Moreover, the SFO space layer
was replaced by CaRu0.8Ti0.2O, which is insulator, the conductivity was further
strengthened. Additional “conducting channels” at the interfaces and the relaxation of
oxygen octahedral tilts arised from a combination of epitaxial strain and oxygen
octahedral connectivity may be the two possible interpretations.
For x=16, a transition temperature (T*) dependent MITs was observed with the
decreasing t CRO except for 0.8 nm and the T* was strongly affected by the thickness of
SFO. The low temperature insulating behavior can be ascribed to the three-dimensional
(3D) weak localization, related to the disorder. Meanwhile the superlattices with t CRO
< 1.6 nm gragually become more insulating which can be explained well by the Motttype and ES-type variable range hopping conduction mechanism. The physical
properties of MITs could be understood within a combined picture of the disorder and
the electron correlation effects. In addition, the signs of magnetoresistance (MR) were
changed at a critical thickness of 1.6 nm of CRO and no matter with the thickness of
SFO. We can’t account for this exactly at present, but a felicitous reason could be the
relaxation of octahedral tilts at the critical thickness. To wit: 1.6nm is the critical
modulated length by octahedral tilts. More research is needed to have an insight into
the physical properties.
Reference:
[1] V. Dobrosavlijevic, G. Kotliar, Phys. Rev. Lett. 78 3943 (1997).
[2] Junwoo Son, James M. LeBeau, S. James Allen, and Susanne Stemmer, Appl.
Phys. Lett. 97.202109 (2010).
[3] Jinwoo Hwang, Junwoo Son, Susanne Stemmer et al, Phys. Rev. B. 87
060101(R) (2013).
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Kondo-Fano resonance in atomic-scale contacts for ferromagnetic
metals
M.S. Islam1, H. Takata1, Y. Ueno1 K. Ienaga2, Y. Inagaki1, H. Tsujii3, T. Kawae1
1Department of Applied Quantum Physics, Kyushu University, Fukuoka, Japan
2Department of Physics, Tokyo Inst. of Technology, Tokyo, Japan
3Department of Education, Kanazawa University, Kanazawa, Japan
The electrical conductance of ferromagnetic atomic-scale contacts prepared by a
Molecular Controllable Break Junction technique has been studied to understand the
origin of Fano resonance observed in ferromagnetic atomic contacts such as Fe [1] and
Ni [2]. In Co atomic-sized contacts, the zero-bias anomaly is well-fitted by the Fano
formula where the Kondo temperature TK is estimated as the fitting parameter.
Moreover, the histogram of TK for more than two hundreds of contacts follows lognormal distribution. These results are consistent with those in ferromagnetic contacts
prepared by a STM technique [1]. We would like to discuss the other transition metals
in the presentation.
Reference:
[1] M. R. Calvo et al., Nature 458, 1150 (2009)
[2] K. Ienaga et al., Phys. Rev. B 86, 064404 (2012)
176
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Modulate metastable states by controlling the reentrance of
antiferromagnetic insulator phase in manganite films
Feng Jin1, Q. Y. Feng3, Q. Y. Lu1,2,3, and W. B Wu1,2,3*
1
Department of Physics, University of Science and Technology of China, Hefei 230026, People’s
Republic of China
2
Technology of China, , Hefei 230026, People’s Republic of China
3
High Magnetic Field Laboratory, Chinese Academy of Sciences, People’s Republic of China
Manganite is one of the prototype strong correlated systems exhibiting intimate
coupling between charge, spin, orbital, and lattice degrees of freedom, resulting in the
delicate energy proximity of different phases. Although the ground state of optimal
doped bulk La2/3Ca1/3MnO3 (LCMO) is FM metal state, LCMO films grown on
NdGaO3(001) suffering anisotropic strain demonstrate a tunable AFM phase or PS state
in a wide temperature range after annealed in O2 atmosphere. Phase separation with the
coexistence of antiferromagnetic insulator phase and ferromagnetic-metal phase (FMM)
was induced in anisotropically strained LCMO/NGO(001) films due to enhanced
orthorhombicity. The reentrance of antiferromagnetic charge-order insulator phase
(AFM-COI) from a saturated ferromagnetic metal phase as functions of magnetic field
and temperature was observed. The reentrance is mediated by the cooperative MnO6
octahedral distortions consistent with the Martensitic-like transformation. The quantity
of the reentrance of the AFM-COI from the saturated FMM can be controlled by
magnetic field and temperature in different processes, however, the resistivity changes
a little in a wide range of temperature. Magnetic force microscopy morphologies exhibit
anisotropically patterns correlating closely with its magnetic and electrical properties.
Reference:
[1] Zhen Huang et al., Phys. Rev. B 86, 014410 (2012).
[2] Haibiao Zhou et al., Nat. Commun. 6, 8980 (2015).
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Effect of interface defects on the magnetoresistance in
Bi4Ti3O12/(La,Sr)Mn1-xO3 heterostructures
Haoliang Huang1, Xiaofang Zhai2, 4, Jianlin Wang3, 4, Dechao Meng2, Yu Yun1, Chao Ma2,
Zhengping Fu1, 2, 4, Yalin Lu1, 2, 3, 4, 5
1
CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and
Engineering, University of Science and Technology of China, Hefei 230026, P. R. China.
2
Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and
Technology of China, Hefei 230026, P. R. China.
3
National Synchrotron Radiation Laboratory, University of Science and Technology of China,
Hefei 230026, P. R. China
4
Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science
and Technology of China, Hefei 230026, P. R. China
5
Laser and Optics Research Center, Department of Physics, United States Air Force Academy,
Colorado 80840, USA.
Heterostructure between bismuth layered ferroelectric oxide Bi4Ti3O12 and
ferromagnetic (La,Sr)Mn1-xO3 is highly interesting due to the need to explore new types
of composite multiferroic systems. But fabricating such heterostructures with high
quality interface is challenging because of the non-isostructural crystal symmetry of the
two constituents. In this work, we constructed two different heterostructures, in which
the Bi4Ti3O12 layers with precisely controlled thickness were deposited on insulating
and conducting (La,Sr)Mn1-xO3 bottom layers, respectively. The results of synchrotron
X-ray absorption and cross-section transmission electron microscopy identified the
intermixing and charge leaking between insulating (La,Sr)Mn1-xO3 and Bi4Ti3O12, but
not between metallic (La,Sr)Mn1-xO3 and Bi4Ti3O12. In the former, the levels of
intermixing and charge leaking are strongly dependent on the thickness of the Bi4Ti3O12
capping layer, which induces capping-layer-thickness dependent magnetoresistance.
These results demonstrate that the interfacial defect is a critical factor for designing
multiferroic heterostructures composed of layered oxide and perovskite oxide.
178
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A paramagnetic ground state in a superconducting multilayer system
U.D. Chacón Hernández1, Carsten Enderlein1, M.A. Sousa1, F.J. Litterst2, E. Baggio-Saitovitch1
1
2
CBPF - Brazilian Center for Research in Physics, RJ, Brazil
Technische Universität Braunschweig Braunschweig, Lower Saxony, Germany
Superconducting spin valves have attracted a lot of attention in recent years. Here,
we present a study on IrMn(15nm)/NiFe(5nm)/Nb(10-50nm)/NiFe(5nm) systems.
Magnetization measurements for systems with a thickness of the superconducting layer
above 30nm reveal a strong response from the superconductor with a hysteresis loop,
which goes in contrary direction of what one would expect from superconducting
systems of such type. Thus, from almost zero magnetization, we find strong
paramagnetism, exhibiting that the hard superconductor Nb compensates for field
changes in the extremely soft ferromagnetic permalloy. This novel effect might pave
the route for the development of future low-temperature electronic devices.
Reference:
[1] Fert, A., Rev. Mod. Phys 80, 1517 (2008)
[2] Chappert, C. and Fert, A. and Van Dau, F. N., Nature Materials 6, 813 (2007)
[3] Gu, J. Y. et al., PRL 89, 267001 (2002)
[4] Moraru, Ion C. and Pratt, W. P. and Birge, Norman O., PRL 96, 037004 (2006)
[5] Zdravkov, V. I. et al., PRB 87, 144507 (2013)
[6] Patiño , E. J. et al. PRB 87, 214514 (2013)
[7] Chacón Hernández , U. D. et al., JMMM 390, 114 (2015)
179
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Measuring the confinement force of vortex-antivortex pairs in a
superconducting Nb film
Ilkyu Yang,1, 2 Jinho Yang,1, 2 Dirk Wulferding,1, 2 Sukmin Chung,2 Roman Movshovich,3 Han
Woong Yeom,1, 2 Ki-Seok Kim,2, 4 and Jeehoon Kim1, 2
1Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science
2Department of Physics, Pohang University of Science and Technology
3MPA-CMMS, Los Alamos National Laboratory
4Institute of Edge of Theoretical Science, Pohang University of Science and Technology
A pair of Abrikosov vortices on the surface of a superconducting medium can be
connected through a quantized magnetic flux inside the superconductor, leading to a
confined vortex-antivortex pair (CVAVP). We describe the creation of CVAVPs using a
novel, home-built magnetic force microscope within a vector magnet, and report the
measurement of the confinement force in CVAVP by supercurrent-induced
manipulation. Applying external magnetic fields to superconductors induces
supercurrents which exert a force onto the vortices, allowing them to overcome their
local pinning potentials. In order to extract the confinement force, we compare pinning
forces of CVAVPs and isolated (unconfined) vortices.
180
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Electromagnetic phase transition in ultrathin LaCoO3 interfacial
layers
Dechao Meng1, Zhicheng Wang1, Haoliang Huang1, Xiaofang Zhai1, Yalin Lu1
1
Perovskite LaCoO3 is a particularly interesting system that bulk LaCoO3 is
diamagnetic at low temperatures1 while tensile-strained LaCoO3 epitaxial films exhibit
ferromagnetic2 ordering near 85 K. This behavior was typically attributed to a strainstabilized spin transition from low-spin to higher-spin (high or intermediate) states3,4.
However, there has been few studies about ultrathin LaCoO3 layers in which the
intricate interactions of interfacial-type of freedoms can potentially induce strong
electronic-phase or magnetic-phase transitions5,6,7. Here high quality LaCoO3 epitaxial
films on TiO2-terminated SrTiO3 substrates with thicknesses from 3 to 30 unit cells
have been synthesized using laser molecular beam epitaxy. Systematic studies of
magnetism, optical spectroscopy and electronic transport have been carried out to
explore the electromagnetic phase transitions enabled by the complex correlation in the
ultrathin interfacial layers. Furthermore, we probe the charge and orbital state using Xray absorption linear dichroism in order to unravel the underlying phase transition
mechanism.
Reference:
[1] P. Raccah et al. PR 155, 932 (1967)
[2] D. Fuchs et al., PRB 75, 144402 (2007)
[3] M. Merz et al., PRB 82, 174416 (2010)
[4] N. Biškup et al., PRL 112, 087202 (2014)
[5] L. Qiao et al., Nano Lett. 15, 4677 (2015)
[6] V. V. Mehta et al., PRB 91, 144418 (2015)
[7] M. Karolak et al., PRL 115, 046401 (2015)
181
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Proximity effect at the interface between the spin-triplet
superconductor Sr2RuO4 and the ferromagnet SrRuO3
M. S. Anwar1, R. Ishiguro2,3,4, Y. Sugimoto1, Y. J. Shin5,6, S. J. Kang5,6, Y. Tano2, S. R. Lee5,6, S.
Yonezawa1, H. Takayanagi2, T. W. Noh5,6, Y. Maeno1
1
Department of Physics, Graduate School of Science, Kyoto University, Kyoto, Japan
2
Department of Applied Physics, Tokyo University of Science, Tokyo Japan
3RIKEN Center for Emergent Matter Science, Saitama, Japan
4
Department of Mathematical and Physical Sciences, Faculty of Science, Women's University,
Japan
5
Center for Correlated Electron Systems, Institute for Basic Science, Seoul, Korea
6
Department of Physics and Astronomy, Seoul National University, Seoul, Korea
Spin-triplet superconducting proximity effect can be generated at an interface
between a spin-singlet superconductor (S) and a ferromagnet (F) but only with the help
of magnetic inhomogeneity at the S/F interface [1]. In such junctions, spin-degree of
freedom is lost. On the other hand, it is difficult to control the complex magnetic
inhomogeneity. These issues can be solved by using a spin-triplet superconductor (T)
and a ferromagnetic hybrid structure. Theoretically, it has been predicted that spintriplet proximity effect at F/T interface can be controlled by magnetization direction of
F relative to the spin direction of the spin-triplet Cooper pairs [2].
We recently developed F/T hybrids by growing epitaxial ferromagnetic SrRuO3 thin
films on the ab-surface of Sr2RuO4 (as a T) single crystals [3,4]. It is observed that
SrRuO3/Sr2RuO4 interface is atomically smooth and highly metallic. Differential
conductance as a function of bias voltage exhibits Andreev reflection feature with
different energy scales. Magnetic field effect reveals the existence of long range
proximity effect without magnetic inhomogeneity. Our work would play an innovative
role in the field of research so called “Superspintronics”.
Reference:
[1] F. S. Bergret et al., Phys. Rev. Lett. 86, 4096 (2001)
[2] P. M. R. Brydon, et al., Phys. Rev. B 88, 054509 (2013)
[3] Y. Maeno, et al., J. Phys. Soc. Jpn. 81, 011009 (2012)
[4] M. S. Anwar, et al., Appl. Phys. Ex. 8, 015502 (2015)
182
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Topological Phases of Proximity-Coupled FerromagnetSuperconductor Junctions
Chien-Te Wu1, Brandon M. Anderson1, Rufus Boyack1, K. Levin1
1
James Franck Institute, University of Chicago, Chicago, IL, USA
Proximity coupled ferromagnet/s-wave superconductor (F/S) junctions have
received much attention due to their applications in the field of cryogenic spintronics.
Although ferromagnetism and s-wave superconductivity are considered to be mutually
exclusive, it is shown both experimentally and theoretically that sz = 1odd-frequency
triplet pairing can be induced by manipulating the orientations of magnetic moments
[1]. The odd-frequency triplet pairing is immune to the pair-breaking exchange field
and its long-range nature offers an avenue to realize superconducting spin valves. The
existence of the odd-frequency triplet pairing has been successfully verified in
experiments via measurements of subgap density of states, superconducting transition
temperatures, and the critical currents in the Josephson junctions. Here we contemplate
the possiblity to generate topological superconductivity in these F/S structures which
has been conjectured to be present [2]. Based on our past work [3,4] using numerical
Bogoliubov-de Gennes formalism on spintronics devices, we study F/S as well as
conical F/S junctions and show that the odd-frequency triplet pairing can coexist with
the px+ipy topological superconducting order in these junctions. Importantly, we discuss
possible experimental signatures such as density of states, I-V curves, and Josephson
currents that help to distinguish these two different triplet pairings. It should be
emphasized that these are a feasible and well studied class of proximity junctions and
should further our understanding of topological superconductors.
Reference:
[1] J. Linder and J. W. A. Robinson, Nat. Phys. 11, 307 (2015).
[2] J. D. Sau, R. M. Lutchyn, S. Tewari, and S. Das Sarma, PRL 104, 040502 (2010).
[3] C.-T. Wu, O. T. Valls, and K. Halterman, PRB 86, 014523 (2012).
[4] C.-T. Wu, O. T. Valls, and K. Halterman, PRB 86, 184517 (2012).
183
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Rigorous analysis of many-electron effects in nanosystems:
Quantum dot - ring nanostructure
A.P. Kądzielawa1, A. Biborski2, A. Gorczyca-Goraj3, E. Zipper3, M. M. Maśka3, and J. Spałek1,2
1
Marian Smoluchowski Institute of Physics, Jagiellonian University, ulica Łojasiewicza 11, 30348 Kraków, Poland
2
Academic Centre for Materials and Nanotechnology, AGH University of Science and Technology,
al. A. Mickiewicza 30, 30-059 Krakow, Poland
3
Department of Theoretical Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice,
Poland
We discuss, on example of quantum dot-ring nanostructure (DRN) [1,2], general
effects coming from the interelectronic Coulomb interactions for Ne=2 and 3 electrons.
Explicitly, we determine many-particle states and calculate accurately also the 3- and
4-state interaction terms, usually omitted in the analysis. For that purpose, the singleparticle wave functions are determined first and represent an input to the subsequent
calculation of the microscopic parameters, which in turn serve as an input in defining
Hamiltonian. The Hamiltonian is diagonalized rigorously with the help of the Lanczos
method [3]. It turns out that both the 3- and 4-state interactions are essential in obtaining
the correct energies for nanosystems, and sometimes, are of comparable magnitude with
the two-state exchange interaction and the so-called correlated hopping terms [4]. With
the increasing size of DRN, the role of two-state interactions becomes dominant. Our
analysis puts on a microscopic basis the Coulomb-blockade effects, as well as
introduces a model system for which we can discuss precisely the role of all terms
representing many-particle interactions in the Hamiltonian.
APK, AB, and JS are supported by the project MAESTRO from Nat. Sci. Centre (NCN),
Grant No. DEC-2012/04/A/ST3/00342, whereas AG-G, EZ, and MMM were supported
by the Grant No. DEC-2013/11/B/ST3/00824.
Reference:
[1] E. Zipper, M. Kurpas, and M.M. Maśka, New J. Phys.14, 093029 (2012).
[2] M. Kurpas, B. Kędzierska, I. Janus-Zygmunt, A. Gorczyca-Goraj, E. Wach, E.
Zipper, and M.M. Maśka, J. Phys.: Condens. Matter 27, 265801 (2015).
[3] A. Biborski, A. P. Kądzielawa, and J. Spałek, Comp. Phys. Commun. 197, 7 (2015).
[4] A. Biborski, A. P. Kądzielawa, A. Gorczyca-Goraj, E. Zipper, M. M. Maśka, and J.
Spałek, in preparation (2016).
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Spin Hall Conductance in Y-shaped Junction Devices
Sudin Ganguly 1, Saurabh Bas1
1
Indian Institute of Technology Guwahati, Assam-781039, India
We study the spin Hall effect in Y-shaped junction devices in presence of Rashba
spin orbit coupling (RSOC). The voltage and the net spin current registered at one of
the arms of the Y-junction are seen to increase, although the spin Hall conductance
(SHC) diminishes as the strength of the RSOC is increased. This implies the voltage
increases faster than that of the current, thereby causing a loss of the RSOC. Various
other characteristic features obtained from our study include, a perfectly asymmetric
behaviour of the spin current and the SHC with respect to the zero bias, while the
voltage shows a symmetric character. Finally, we find that a large RSOC completely
destroys the SHC, owing to a complete disappearance of the local density of states,
thereby reinforcing our earlier claim that RSOC emulates the effect of disorder on the
quantum conductance of junction devices.
185
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Theoretical Study of Effects of Twin Boundary and Metastable
States on Nano-scaled Superconducting Composite Structure (d-dot)
Norio Fujita1, Masaru Kato1, Takekazu Ishida2
1
2
Department of Mathematical Sciences, Osaka Prefecture University, Sakai, Osaka, Japa
Department of physics and Electronics, Osaka Prefecture University, Sakai, Osaka, Japan
A d-dot is a nano-sized composite structure that consists of a d-wave superconductor (SC)
embedded in an s-wave matrix, as shown in Fig.1(a). Due to the superconducting order
parameter symmetry in the d-wave SC, phase difference appears at corner junctions between dand s-wave SCs in d-dot’s. Compensating this phase difference, spontaneous half-quantized
vortices (SHQVs) appear in d-dot’s [1].
But it is pointed out that the SHQVs may not appear if there exist phase differences across
twin boundaries (TBs) in YBa2Cu3O7- δ (YBCO) [2].
In order to analyze effects of TBs on SHQVs, we introduce orthorhombic structure of YBCO
to two-components Ginzburg-Landau(GL) equations [2] in terms of anisotropy of effective
mass in YBCO. Then we derived following modified two-component GL equations.
Using the finite element method [1] and solving these equations self-consistently, we
investigate the effects of TBs on SHQVs. Results show that anisotropy of effective mass
suppress SHQVs [3] and that fractional vortices appear on edges of TB due to supercurrent
jump across TB around the boundaries of d- and s- wave SCs (Fig.1(c) and (d)).
Fig. 1 Schematic diagrams of d-dot (a) without TB and (c) with TB. (b) and (d) are
magnetic field distributions for (a) and (c), respectively.
Reference:
[1] M. Kato, T. Ishida, T. Koyama, M. Machida, Superconductors – Materials,
Properties and Applications. (InTech 2012) Chap. 13.
[2] Hilgenkamp et al., Nature, 422, (2003) 50.
[3] N. Fujita, M. Kato, T. Ishida, Physica C, 518, (2015) 44-46.
186
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Dimensional Crossover from 2D Fermi Liquids to 1D Luttinger
Liquids
Jia-Hua Gu, Kai Sun
Department of Physics, University of Michigan-Ann Arbor, Ann Arbor, Michigan, USA
We demonstrate an analytic theory for the crossover between Fermi liquids and
Luttinger liquids. By deforming the Fermi surface of a 2D Fermi liquid towards perfect
nesting, we show that signatures of Luttinger liquids arise. In the crossover regime,
bosonic particles emerge from the fermionic theory, whose spectral weight
characterizes the crossover towards 1D Luttinger liquids. At perfect nesting, these
bosonic modes recover the bosonization formalism for Luttinger liquids. Spin-charge
separation is also studied.
187
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Correlations between electron localization and magnons in
SrRuO3/SrIrO3 superlattices
Bin Pan1, Lunyong Zhang 1, 2, Y.B. Chen3, Yanfeng Chen1
1
National Laboratory of Solid State Microstructures and Department of Materials Science and
Engineering, Nanjing University, Nanjing 210093, China
2
Max Planck POSTECH Center for Complex Phase Materials and Department of Physics,
Pohang University of Science and Technology, Pohang 790-784, Korea
3
National Laboratory of Solid State Microstructures & Department of Physics, Nanjing
University, 210093 Nanjing, China
SrRuO3 is a particular itinerant ferromagnetic perovskite oxide with unsolved
controversies that if the frequent observed spin glass state in it is a real ground state and
if it is in vicinity of a quantum critical point. Here the transport and magnetic behaviors
of superlattices integrating SrRuO3 and strong spin orbit coupling semimetal SrIrO3
were studied. Strong electron localization, spin wave magnon interactions and Stoner
excitations were revealed accompany with the formation of spin glass state at low
temperature, indicating that disorder would be the driving mechanism of spin glass state.
It was demonstrated the strengths of spin wave magnon interactions , Stoner excitations,
as well as the electron magnon scattering are strong correlated with the electron
localization strength, bearing increase trend with the enhancement of electron
localization, through comparisons in the superlattices with constant SrRuO3 layer
thickness but different SrIrO3 layer thicknesses. These results suggest that electron
localization generates basic quantum scale corrections in itinerant magnets not only to
charge transport processes but also to the spin associated processes such as spin wave
excitations and magnetic ordering states.
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Electrical resistivity of Chromium thin film
M. Ohashi1,2, S. Tateno2, T. Kubota3, K. Takanashi3
1Institute of Science and Engineering, Kanazawa University, Kanazawa, Japan
2
Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan
3
Institute for Materials Research, Tohoku University, Sendai, Japan
We studied the electrical resistance of single-crystal and polycrystalline chromium
films. The ρ(T) curve of single-crystal films decrease with decreasing temperature and
show humps at around 300 K consistent with the bulk chromium being an itinerant
antiferromagnet[1]. On the other hand, semiconducting behavior is observed in the
electrical resistance of polycrystalline films, indicating that the two-dimensional
conductivity is probably important. Moreover, no anomaly was detected by resistance
measurements around room temperature. Such behavior may be attributed to the
suppression of antiferromagnetic interaction by thinning down the chromium element.
Reference:
[1] M. Ohashi, and G. Oomi, Jpn. J. Appl. Phys., 48, 070221 (2009).
189
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Strong charge density wave fluctuation and sliding state in PdTeI
with quasi-1D PdTe chains
Hechang Lei1,2,3, Kai Liu1, Jun-ichi Yamaura3, Sachiko Maki3, Youichi Murakami4, ZhongYi Lu1, and Hideo Hosono2,3
1
Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials
& Micro-nano Devices, Renmin University of China, Beijing 100872, China
2
Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503,
Japan
3
Materials Research Center for Element Strategy, Tokyo Institute of Technology, Yokohama 2268503, Japan
4
Institute of Materials Structure Science, High Energy Accelerator Research
Organitization (KEK), Tsukuba, Ibaraki 305-0801, Japan
In quasi-one-dimensional (quasi-1D) system, the charge density wave (CDW)
transition temperature TCDW is usually lower than the mean-field-theory predicted TMF
and a CDW fluctuation region exists between them. Here, we investigate the physical
properties of PdTeI single crystal containing quasi-1D PdTe chains. Surprisingly, we
find that the carrier concentration decreases gradually before the long-range CDW
ordering state occurring at T1 ~ 110 K, reflecting the existence of strong CDW
fluctuation with possible pseudogap state at T>>T1 because of dynamic charge
separation of Pd ions (Pd3+ → Pd2+ + Pd4+). Moreover, the sliding CDW state appears
below T2 ~ 6 K. Combined such low T2 with the feature of multiple quasi-1D bands,
PdTeI exhibits exotic crossover behavior from negative to huge positive
magnetoresistance under magnetic field and field-induced localization. Thus, PdTeI
provides a novel platform for studying the CDW fluctuation and the interplay between
magnetic field and CDW state.
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Consistent Bosonization-Debosonization: a new path forward
C.J. Bolech Nayana Shah
Department of Physics, University of Cincinnati , Ohio, USA
We critically reexamined the Bosonization-Debosonization (BdB) procedure for
systems including certain types of localized features (more general scenarios are also
possible). By focusing on the case of a tunneling junction out of equilibrium, we have
shown that the conventional approach to BdB gives results that are not consistent with
the exact solution of the problem, even at the qualitative level, and highlighted the
inconsistencies that can adversely affect the results of all types of calculations. We
subsequently introduced a Consistent BdB procedure that we developed to resolve the
aforementioned non-equilibrium transport puzzle and argued that this framework
should be widely applicable [1]. We substantiated the last claim by applying the
updated procedure to the two-lead Kondo problem [2], which besides being a key
theoretical prototype of a strongly correlated system away from equilibrium, is also of
immediate experimental relevance in many ways.
References:
[1] Nayana Shah and C. J. Bolech, arXiv:1508.03078 (to appear in Phys. Rev. B).
[2] C. J. Bolech and Nayana Shah, arXiv:1508.03079 (to appear in Phys. Rev. B).
191
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Non-equilibrium transport in the single impurity Anderson model: a
renormalized dual-fermion approach
E. Muñoz1 and S. Kirchner2
1
2
Physics Institute, Pontificia Universidad Católica de Chile, Santiago, Chile
Center for Correlated Matter and department of Physics, Zhejiang University, Hangzhou, China
Thelow-temperature, low-bias non-linear conductance characteristics in
semiconductor quantum dots and single-molecule transistors present some universal
features, arising as a signature of the local Fermi liquid regime. We have studied the
role of level asymmetry (gate voltage) and local Coulomb repulsion (charging energy)
on the low-temperature and low-field scaling properties of the non-linear conductance
of such a system, as described by the single impurity Anderson model [1-3]. For this
purpose, we used our recently developed method of renormalized perturbation theory
in terms of dual fermions, with a particle-hole symmetric reference system [1,2]. We
have compared our analytical results with numerical renormalization group calculations
[3,4], thus finding perfect agreement at particle-hole symmetry up to the Kondo limit,
and an excellent quantitative agreement even at relatively large finite level asymmetry.
Moreover, our results have recently provided a theoretical framework to fit and interpret
magneto-transport experiments in single-molecule transistors [5].
References:
[1] E. Muñoz, C. J. Bolech and S. Kirchner. Phys. Rev. Lett. 110, 016601 (2013).
[2] E. Muñoz, C. J. Bolech and S. Kirchner. Phys. Rev. Lett. 111, 089702 (2013).
[3] L. Merker, S. Kirchner, E. Muñoz and T. A. Costi. Phys. Rev. B 87, 165132
(2013).
[4] L. Merker, S. Kirchner, E. Muñoz and T. A. Costi, Phys. Rev. B 90, 077102
(2014).
[5] G. D. Scott, D. Natelson, S. Kirchner and E. Muñoz, Phys. Rev. B 241104(R)
(2013).
192
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Superconducting-normal single-molecular junctions - beyond the
Blonder- Tinkham - Klapwijk paradigm
P. Ribeiro1, J. Brand2, N. Néel2, S. Kirchner3, and J. Kröger2
1
CeFEMA, Instituto Superior Técnico, Universidade de Lisboa Av. Rovisco Pais, 1049-001
Lisboa, Portugal
2
Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany
3
Center for Correlated Matter, Zhejiang University, Hangzhou, Zhejiang 310058, China
The Blonder-Tinkham-Klapwijk (BTK) theory [1], originally developed for
superconducting (SC)-normal (N) point contacts in the ballistic transport regime, has
been extended to diffusive point contacts [2] and to the tunnelling spectroscopy of
unconventional superconductors [3]. The dependence of the BTK effective parameters
on the internal structure of the junction, however, remains unclear.
Here, we analyze the differential conductance characteristics of a microscopic model
for SC-N molecular junctions and compare to the predictions of BTK both in the
tunnelling and contact regimes. We find that the BTK results are recovered whenever
the hybridisation of the molecule with either the SC of the N metal is much larger than
the energy scales associated with the internal structure of the junction. For the opposite
regime, we discuss the influence of the hybridisation on the evolution of the currentvoltage curves with bias voltage across the SC gap. Finally, a comparison of our
theoretical results with scanning tunnelling spectroscopy of C_60 spectroscopy of C60
molecules deposited on a Niobium surface highlights the influence of the electrodes’
atomic-scale structure on the charge transport across the SC-N interface, as observed
by the spectral signature of Andreev reflections in these junctions.
Reference:
[1] G. E. Blonder, M. Tinkham, and T. M. Klapwijk, Phys. Rev. B 25, 4515 (1982)
[2] C.W.J. Beenakker, Rev. Mod. Phys. 69, 731 (1997)
[3] Yukio Tanaka and Satoshi Kashiwaya,Phys. Rev. Lett. 74, 3451(1995)
193
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Controlling the Mott insulating state in Ca2RuO4 under
non-equilibrium conditions
C. Sow1, S. Yonezawa1, F. Nakamura2, T. Oka3, 4, S. Kitamura5, K. Kuroki6, and Y. Maeno1
1
2
3
4
Kyoto University, Kyoto, Japan
Kurume Institute of Technology, Kurume, Japan
Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
5
University of Tokyo, Tokyo, Japan
6
Osaka University, Osaka, Japan
Application of electric-field or current can induce novel electronic states in strongly
correlated systems. Our main focus is to induce new phases under non-equilibrium
conditions such as under flowing DC current in correlated systems. In this regard,
Ca2RuO4 (CRO) is a promising candidate in which one can expect new emergent
phenomena especially at low temperatures. CRO is a Mott insulator that becomes a
good metal by suitable stimuli such as chemical doping [1], pressure, temperature or
electric field [2]. It is also shown that the Mott gap decreases with current [3].
In this presentation, we report the results of magnetization and transport
measurements performed on high-quality CRO single crystals. We have made a special
sample holder to be used in a commercial SQUID magnetometer to measure the
resistance and magnetization simultaneously under current. We have placed a
thermometer close to the sample in order to measure the actual temperature of the
sample.
We found that flowing DC current strongly hinders the insulating behavior and
changes the magnetic behavior in CRO.
[1] At 100 K the resistance is reduced by more than 5 orders of magnitude in 5 mA
current.
[2] A small current (< 2 mA) is sufficient to suppress the AFM ordering.
[3] At low temperature (~50 K) a sharp decrease in magnetization is noticed, although
there is no signature of superconductivity down to 20 K.
Such sensitive changes of the Mott insulating state under DC current provide a
promising future direction in the study of strongly-correlated electron systems.
References:
[1] S. Nakatsuji and Y. Maeno, Phys. Rev. Lett. 84, 2666 (2000).
[2] F. Nakamura et al., Sci. Rep. 3, 2536 (2013).
[3] R. Okazaki et al., J. Phys. Soc. Jpn. 82, 103702 (2013).
194
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Giant effect of isovalent doping on magnetism in BaFe2(As1-xPx)2
J. Pelliciari1, Y. Huang1, 2, K. Ishii3, M. Dantz1, P. Olalde Velasco1, V. Strocov1, X. Wang2, L.
Xing2, C. Q. Jin2, X. Lu1, T. Watashige4, S. Kasahara4, T. Shibauchi4,5, T. Das6, and T. Schmitt1
1
2
Swiss Light Source, Paul Scherrer Institut, Villigen PSI, Switzerland
Beijing National Lab for Condensed Matter Physics, Institute of Physics, Chinese Academy
of Sciences, Beijing, China
3
SPring-8, Japan Atomic Energy Agency, Sayo, Hyogo, Japan.
4
Department of Physics, Kyoto University, Kyoto City, Japan
5
Department of Advanced Materials Science, Tokyo University, Chiba,
6
Department of Physics, Indian Institute of Science, Bangalore, India
Superconductivity in iron pnictides was discovered in 2008 [1] and since then a lot
of effort has been devoted to explain their unconventional nature. As in other high
temperature superconductors, magnetism and superconductivity (SC) exhibit proximity,
competition and / or coexistence in the phase diagram, indicating strong connections
between them [2, 3, 4]. In this context, the experimental characterization of static and
dynamic magnetism is of vital importance in constraining advanced theoretical models.
The BaFe2(As1-xPx) 2 series is an interesting case because SC appears with isovalent
doping without changing the number of carriers [2,4].
We present a combined Fe L3 RIXS and Kβ X-ray emission spectroscopy (XES)
study of parent and doped BaFe2(As1-xPx)2 spanning a large portion of the phase
diagram. RIXS measurements reveal the persistence of broad dispersive magnetic
excitations in all doping levels. Remarkably, the energy of such modes is strongly
hardening with doping contrasting the case of hole-doped BaFe2As2 [6]. Additionally,
XES experiments show quenching of the local magnetic moment for increasing P
doping. Employing calculations of spin and charge susceptibility we link this
unconventional evolution of the magnetism to a shift from 2- to 3-dimensional physics
in this system, which is manifested in the phenomenon of Fermi surface warping.
References
[1]Y. Kamihara et al, J. Am. Chem. Soc. 130, 3296 (2008)
[2]G. R. Stewart, Rev. Mod. Phys. 83, 1589 (2011)
[3]D. J. Scalapino, Rev. Mod. Phys. 84, 1383 (2012)
[4]D. C. Johnston, Advances in Physics Vol. 59, No. 6, 803 (2010)
[5]L. J. P. Ament et al, Rev. Mod. Phys. 83, 705 (2011)
[6]K. J. Zhou et al, Nat. Comm. 4, 1470 (2013)
195
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Multiband thermal transport in the iron-based superconductor
Ba1-xKxFe2As2
Marcin Matusiak1,* and Thomas Wolf2
1
Institute of Low Temperature and Structure Research, Polish Academy of
Sciences, ul. Okolna 2, 50-422 Wroclaw, Poland
2
Institute of Solid State Physics (IFP), Karlsruhe Institute of Technology, D76021, Karlsruhe, Germany
We present results of precise measurements of the thermal and electrical transport in
the optimally- and over-doped Ba1-xKxFe2As2 single crystals (x = 0.35, 0.55, 0.88) and
compare them to the previously reported data on Ba(Fe1-yCoy)2As2. A contraction of the
electron pocket is observed upon substitution potassium for barium, but even at the
extreme doping (x = 0.88) there is still a noticeable contribution from negative charge
carriers to the electronic transport. The size of the electron pocket in all K-doped
samples is small enough to cause a significant enhancement of the respective HallLorenz number.
Another observed characteristic is the emergence of a maximum in the transverse
thermal conductivity below the superconducting critical temperature of the optimally(x = 0.35) and slightly over-doped (x = 0.55) samples. The evolution of this anomaly
from the optimally electron-doped Ba(Fe0.94Co0.06)2As2 to hole-overdoped
Ba0.45K0.55Fe2As2 suggests formation of a uniform superconducting gap on the electron
pocket in the former and regions of a depressed gap on the hole-pocket in the latter.
196
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Unusual nematic state in 122-type iron-based superconductor near
optimal doping
Jun Li,1,2,3 Jie Yuan,4,2 Paulo J. Pereira,3,5 Meng-Yue Li,1,2 Yang-Yang Lv, 1 Zi-Quan Lin,6 YongJie Liu,6 Jun-Feng Wang,6 Liang Li,6 Johan Vanacken,3 Liviu F. Chibotaru,5 Victor V.
Moshchalkov,3 Kazunari Yamaura,2,7 Eiji Takayama-Muromachi,2,7 Hua-Bing Wang,1,2 Pei-Heng
Wu1
1
Research Institute of Superconductor Electronics, Nanjing University, Nanjing 210093, China
2
National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
3
4
INPAC-Institute for Nanoscale Physics and Chemistry, KU Leuven, Celestijnenlaan 200 D,
Leuven B-3001, Belgium
National Laboratory for Superconductivity, Institute of Physics, and Beijing National Laboratory
for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100080, China
5
Division of Quantum and Physical Chemistry and INPAC-Institute for Nanoscale Physics and
Chemistry, KU Leuven, Celestijnenlaan 200F, Leuven B-3001, Belgium
6
7
Department of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060 -0810,
Japan
Nematic states are present in many superconductors, breaking the symmetry between
the x and y directions of the crystal. Usually the origin of these nematic states is a
structural or electronic-orbital or spin-fluctuation- instability. In case of iron-based
superconductors, an anti-ferromagnetic phase is present simultaneously to a nematic
state which is presently believed to be of spin fluctuation origin. Here we exhibit a
nematic state found in Ba0.5K0.5Fe2As2 which the origin is none of those mention above
in temperature below the Tc under both static fields and pulsed high magnetic fields up
to 57 T. This nematic state has no manifestation on the normal current state of the
material and arises immediately at the nucleation of superconductivity. The nature of
this state seems to be intrinsically related with the superconducting phenomena.
Moreover, the presence of two degenerate-s-wave and d-wave components of the
superconducting order parameter develops a nematic state with similar characteristics
to those observed experimentally, and we find it as the simplest and best explanation
for this phenomenon.
Reference:
[1] J. Li et al., in preparing.
[2] R. M. Fernandes, A. V. Chubukov, and J. Schmalian, Nat. Phys. 10, 97 (2014
197
Mo-P078
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A unifying phase diagram with correlation-driven
superconductor -to-insulator transition for the 122* series of
iron-chalcogenides
X. H. Niu,1,2 S. D. Chen,1 J. Jiang,1,2 Z. R. Ye,1,2 T. L. Yu,1,2 D. F. Xu,1,2 M. Xu,1,2 Y. Feng,1, 2
Y. J. Yan,1, 2 B. P. Xie,1, 2 J. Zhao, 1, 2 D. C. Gu,3 L. L. Sun,3, 4 Qianhui Mao,5 Hangdong Wang,5
Minghu Fang,5, 2 C. J. Zhang,6, 2 J. P. Hu,3, 4 Z. Sun,7, 2, ∗ and D. L. Feng1, 2, †
1
State Key Laboratory of Surface Physics, Department of Physics,and! Advanced Materials
Laboratory, Fudan University, Shanghai 200433, People’s Republic of China
2
Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People’s Republic of
China
3
4
Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
Collaborative Innovation Center of Quantum Matter, Beijing 100190, People’s Republic of China
5
6
Department of Physics, Zhejiang University, Hangzhou, 310027, People’s Republic of China
High Magnetic Field Laboratory, Chinese Academy of Sciences and Universityof! Science
and Technology of China, Hefei 230026, People’s Republic of China
7
Hefei, Anhui 230029, People’s Republic of China
The 122∗ series of iron-chalcogenide superconductors, for example KxFe2−ySe2,
only possesses electron Fermi pockets. Their distinctive electronic structure challenges
the picture built upon iron pnictide superconductors, where both electron and hole
Fermi pockets coexist. However, partly due to the intrinsic phase separation in this
family of compounds, many aspects of their behavior remain elusive. In particular, the
evolution of the 122∗ series of iron-chalcogenides with chemical substitution still lacks
a microscopic and unified interpretation. Using angle-resolved photoemission
spectroscopy, we studied a major fraction of 122∗ iron-chalcogenides, including the
isovalently ‘doped’ KxFe2−ySe2−zSz, RbxFe2−ySe2−zTez and (Tl,K)xFe2−ySe2−zSz. We
found that the bandwidths of the low energy Fe 3d bands in these materials depend on
doping; and more crucially, as the bandwidth decreases, the ground state evolves from
a metal to a superconductor, and eventually to an insulator, yet the Fermi surface in the
metallic phases is unaffected by the isovalent dopants. Moreover, the correlation-driven
insulator found here with fractional band filling may be a novel insulating phase. Our
study shows that almost all the known 122∗-series iron chalcogenides can be understood
via one unifying phase diagram which implies that moderate correlation strength is
beneficial for the superconductivity.
198
Mo-P079
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Reversible Tuning of the Collapsed Tetragonal Phase Transition in
CaFe2As2 by separate control of chemical pressure and electron
doping
K. Zhao1, C. Stingl1, R. S. Manna1, C.Q. Jin2, 3, and P. Gegenwart1
1
Experimentalphysik VI, Center for Electronic Correlations and Magnetism, Augsburg University,
86159 Augsburg, Germany
2
Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese
3
Single crystals of Ca(Fe1−xRux)2As2 (0≤x≤0.065) and Ca1-yLay(Fe0.973Ru0.027)2As2
(0≤y≤0.2) have been synthesized and studied with respect to their structural, electronic
and magnetic properties. The partial substitution of Fe by Ru induces a decrease of the
c-axis constant leading for x<0.023 to the suppression of the coupled magnetic and
structural (tetragonal to orthorhombic) transitions. At x≤0.023 a first order transition to
a collapsed tetragonal (CT) phase is found, which behaves like a Fermi liquid and which
is stabilized by further increase of x. The absence of superconductivity near xcr is
consistent with truly hydrostatic pressure experiments on undoped CaFe2As2. Starting
in the CT regime at x=0.027 we investigate the additional effect of electron doping by
partial replacement of Ca by La. Most remarkably, with increasing y the CT phase
transition is destabilized and the system is tuned back into a tetragonal ground state at
y≥0.08. This effect is ascribed to a weakening of interlayer As-As bonds by electron
doping. Upon further electron doping filamentary superconductivity with Tc of 41 K at
y=0.2 is observed.
Reference:
[1] K. Zhao et al., PRB 92, 235132 (2015)
199
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Complementary Neutron and X-ray Studies about the Magnetism in
EuFe2As2-based Iron Pnictides
W. T. Jin1, Y. Xiao2, Y. Su1, S. Nandi3, W. H. Jiao4, G. H. Cao5, Th, Brückel1, 2
1
Jülich Center for Neutron Science JCNS at Heinz Maier-Leibnitz Zentrum (MLZ),
Forschungszentrum Jülich GmbH, Garching, Germany
2
Jülich Center for Neutron Science JCNS and Peter Grünberg Institut PGI, JARA-FIT,
Forschungszentrum Jülich GmbH, Jülich, Germany
3
Department of Physics, Indian Institute of Technology, Kanpur, India
4
School of Science, Zhejiang University of Science and Technology, Hangzhou,China
5
Among various parent compounds of the Fe-based superconductors, EuFe2As2 is a
unique member of the ternary “122” AFe2As2 (A = Ba, Sr, Ca, etc) family since it
contains two magnetic sublattices and the A site is occupied by the S-state rare-earth
Eu2+ ion possessing a 4f 7 electronic configuration with an electron spin S = 7/2 [1].
Recently, we have investigated the magnetic ground states in superconducting
Eu(Fe1−xCox)2As 2 (x = 0.18) [2], EuFe2(As1−xPx)2 (x = 0.15 and 0.19) [3, 4], and
Eu(Fe1−xIrx)2As2 (x = 0.12) [5] samples by single-crystal neutron diffraction and x-ray
resonant magnetic scattering (XRMS) measurements, respectively. The Eu2+ moments
were found to be ferromagnetically aligned along the crystallographic c direction in the
ground state, coexisting with the superconductivity. The coexistence of ferromagnetism
and superconductivity is intriguing and a possible spontaneous vortex state might be
responsible for the compromise between such two antagonistic phenomena. In addition,
our recent XRMS measurements on a non-superconducting Eu(Fe1−xIrx)2As2 (x = 0.06)
sample [6] reveals possible interplay between the localized Eu2+ moments and the
conduction d-electrons on the FeAs layers.
Reference:
[1] Y. Xiao et al., PRB 80, 174424 (2009).
[2] W. T. Jin et al., PRB 88, 214516 (2013).
[3] S. Nandi et al., PRB 89, 014512 (2014).
[4] S. Nandi et al., PRB 90, 094407 (2014).
[5] W. T. Jin et al., PRB 91, 064506 (2015).
[6] W. T. Jin et al., accepted by PRB.
200
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Chemical Pressure Effect on the Superconductivity of Iron-based
Superconductors
Kangkang Hu, Bo Gao, Gang Mu*, Xiaoming Xie
State key Laboratory of Functional Materials for Informatics and Shanghai Center for
Superconductivity, Shanghai Institute of Microsystem and Information Technology, Chinese
Academy of Sciences, Shanghai, China
The pressure effect on the superconductivity of iron-based superconductors is an
important issue, which is under debate at present. In the present work, we investigated
the effects of P-substitution induced chemical pressure on the superconductivity of
electron-doped SrFe2-xCoxAs2 series with different Co doping levels. It is found that
the superconducting transition temperature Tc can be scaled to a uniform curve with an
effective doping number xeff=x+y/4.5, where y is the concentration of P doping. Our
results suggest that further P substitution induces a net electron-doping effect in the
present system. A further analysis considering other reports indicates that the pressure
tends to enhance the charge carriers that dominate in this multi-band system.
201
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Vortex pinning and penetration depth in the over-doped
supercond -uctor (B𝑎1−𝑥𝐾𝑥)2A𝑠2
Hoon Kim,1 Ilkyu Yang,1,2 Dirk Wulferding,1,2 Dongil Im,1,2 Bing Shen,3 K. Cho,4 R.
Prozorov,4,5 Han Woong Yeom,1,2 and Jeehoon Kim1,2
1
Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
2
Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, 77
Cheongam-Ro, Nam-Gu, Pohang 790-784, Korea
3
Center for Superconducting Physics and Materials, National Laboratory of Solid State
Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
4
Ames Laboratory, Ames, Iowa 50011, USA
5
Department of Physics & Astronomy, Iowa State University, Iowa 50011, USA
(B𝑎1−𝑥𝐾𝑥)𝐹𝑒2A𝑠2 is a hole-doped 122 iron pnictide superconductor with its
superconducting dome extending across the whole doping range. While it shows
isotropic s-wave superconductivity at the optimal doping x ≈ 0.4 [1], a significant gap
anisotropy emerges in the under-doped regime, due to a competition between and
coexistence of antiferromagnetism/nematicity and superconductivity [2]. In contrast, in
the over-doped regime the superconductivity is characterized by a nodal line in its gap
structure, together with a Lifshitz transition at x ≈ 0.7 [3,4,5]. We present a low
temperature magnetic force microscopy (MFM) study on overdoped samples ( x = 0.47,
0.54, 0.7). Using a comparative method we extract the absolute values of the London
penetration depth λ. In addition, we estimate the pinning force of single Abrikosov
vortices via tip-vortex interaction. Our results show that, at x ≈ 0.7 where a Fermi
surface topography alteration occurs, the pinning force drastically diminishes without
a significant change in λ, violating the commonly observed inversely proportional
relationship between them.
Reference:
[1] K. Cho, et. al., Phys. Rev. B 90, 104514 (2014).
[2] H. Kim, et. al., Phys. Rev. B 90, 014517 (2014).
[3] Sergey L. Bud’ko, et. al., Phys. Rev. B 87, 100509 (2013).
[4] N. Xu., et. al., Phys. Rev. B 88, 220508 (2013).
[5] Halyna Hodovanets, et. al., Phys. Rev. B 89, 224517 (2014).
202
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Complex Fermi surface evolution with temperature in CaFe2 As2
Khadiza Ali1, Swapnil Patil1, Ganesh Adhikary4, Sangeeta Thakur3, Sanjoy Mahatha2, Carlo
Carbone2, G. De Ninno4, L. Petaccia3, A. Thamizhavel1, S. K. Dhar1 and Kalobaron Maiti1
1
2
Tata Institute of Fundamental Research, Mumbai, India
Istituto di Struttura della Materia Consiglio Nazionale delle Ricerche, Trieste, Italy
3
Elettra Sincrotrone Trieste, Strada Statale 14 km 163.5, 34149 Trieste, Italy
4.
University of Nova Gorica, Slovenia
We have carried out Angle Resolved Photoemission (ARPES) measurements on
CaFe2 As2 , which is one of the parent compound studied extensively to understand the
high temperature superconductivity in Fe-based systems. CaFe2 As2 undergoes a
concomitant transition to a spin-density wave (SDW) state and tetragonal to
orthorhombic structure at about 170 K. ARPES measurements showed an evolution
from 2D to 3D Fermi surface across this temperature as a signature of structural change
and Fermi surface nesting representing the SDW phase. Our ARPES results exhibit
signature more complex Fermi surface evolution with temperature with additional
contribution from a collapsed tetragonal phase although the collapsed tetragonal
structure appears only in some special conditions. Evolution of the Fermi surface with
temperature is also anomalous. While the material in orthorhombic phase exhibit
superconductivity at high pressure or with doping, the collapsed tetragonal phase do
not show superconductivity. Thus, our results with the signature of two phases in the
electronic structure suggests that the electronic properties of these systems are complex
and calls for more study in this direction.
203
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Manifestation of electron correlation on spin excitations in
Ba1−𝑥 K 𝑥 Fe2 As2 superconductors
Ke-Jin Zhou1
1
Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0DE, UK
The discovery of superconducting iron-based pnictides and chalcogonides provide
a new route to the understanding of unconventional superconductors (SCs) apart from
cuprates. The week-coupling scenario was proposed initially in which the nesting is
believed to be crucial for the electron. On the contrary, the parent pnictides and
chalcogenides are bad metals with considerable electron correlation thus suggesting
a strong-coupling approach favouring large localized magnetic fluctuating moments.
Recent development of the momentum-resolved resonant inelastic X-ray scattering
(RIXS) technique [1] have enabled investigations of magnetic excitations in cuprates
[2,3,4], which show excellent agreement with results from Inelastic Neutron Scattering.
In this presentation, we report RIXS studies on spin excitations in parent BaFe2 As2 (BFA)
and hole-doped Ba1−𝑥 K 𝑥 Fe2 As2 (x=0.25, 0.4, 0.6) (BKFA0.25, BKFA0.4, and
BKFA0.6) superconductors [5, 6]. For BFA, spin excitations present throughout the
temperature range from 15K to 300K. Clear spin-excitations softening sets in around TN
of 140K when warmed up from the antiferromagnetic ordered phase to the paramagnetic
phase. Upon the hole-doping, spin excitations well persist even for the over-doped
BKFA0.6 accompanied by sizable softening across the probed reciprocal space. Based on
a combined density function theory with dynamical mean field theory, the calculated
dynamical spin susceptibilities show good agreement with the spin-excitations spectra.
We demonstrate that the spin excitations in iron pnictides intimately interact with the
electronic structure (charge and orbital degrees of freedom) with its softening driven by
the strength of electronic correlation [6].
Reference:
[1] G. Ghiringhelli et al., Rev. Sci. Instrum. 77, 113108 (2006); V. N. Strocov et al.,
J. Synch. Radiat. 17, 631 (2010).
[2] J. Schlappa et al., Phys. Rev. Lett. 103, 047401 (2009).
[3] L. Braicovich et al., Phys. Rev. Lett. 104, 077002 (2010).
[4] M. Le Tacon et al., Nature Phys. 7, 725 (2011).
[5] K. J. Zhou et al., Nature Communications 4, 1470 (2013).
[6] K. J. Zhou et al., in preparation.
204
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Spin excitations in optimally P-doped BaFe2(As0.7P0.3)2
superconductor
Ding Hu1, *, Zhiping Yin2, 3, *, Wenliang Zhang1, R. A. Ewings4, Kazuhiko Ikeuchi5, Mitsutaka
Nakamura6, Bertrand Roessli7, Yuan Wei1, Lingxiao Zhao1, Genfu Chen1, Shiliang Li1, 8, Huiqian
Luo1, Kristjan Haule3, Gabriel Kotliar3, and Pengcheng Dai9, 2, †
1
Beijing National Laboratory for Condensed Matter Physics,Institute of Physics, Chinese
2
Department of Physics and the Center of Advanced Quantum Studies, Beijing Normal University,
Beijing 100875, China
3
Department of Physics, Rutgers University, Piscataway, NJ 08854, USA
4
ISIS Facility, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot, OX11 0QX,
United Kingdom
5
Research Center for Neutron Science and Technology,Comprehensive Research Organization for
Science and Society (CROSS), Tokai, Ibaraki 319-1106, Japan
6
Materials and Life Science Division, J-PARC Center, Tokai, Ibaraki 319-1195, Japan
7
Laboratory for Neutron Scattering and Imaging,Paul Scherrer Institut, CH-5232 Villigen,
Switzerland
8
9
Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA
We use inelastic neutron scattering to study temperature and energy dependence of
spin excitationsin optimally P-doped BaFe2(As0.7P0.3)2 superconductor (Tc = 30 K)
throughout the Brillouinzone. In the undoped state, spin waves and paramagnetic spin
excitations of BaFe2As2stem from antiferromagnetic (AF) ordering wave vector QAF =
(±1, 0) and reach zone boundary at (±1,±1)around 200 meV. Replacing 30% As by
smaller P to induce superconductivity, low-energy spin excitationsof BaFe2(As0.7P0.3)2
form a resonance and high-energy spin excitations extend to about 300 meV near
(±1,±1). These results are consistent with calculations from a combined density
functional theory and dynamical mean field theory, and suggest that the decreased
average pnictogenheight in BaFe2(As0.7P0.3)2 reduces the strength of electron
correlations and increases the effectivebandwidth of magnetic excitations.
Reference:
[1] Ding Hu et al.,unpublished
205
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Antiferromagnetism and transport properties in non-superconducting
iron pnictide BaFe2−2xNixCrxAs2
Rui Zhang1, Dongliang Gong1, Xingye Lu1, Shiliang Li1, Mark Laver2, Christof Niedermayer2,
Sergey Danilkin3,Guochu Deng3, Pengcheng Dai4, and Huiqian Luo1,
1
Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
2
Paul Scherrer Institute, CH-5232 Villigen, Switzerland
3
Bragg Institute, Australian Nuclear Science and Technology Organization, Australia
4
Department of Physics and Astronomy, Rice University, USA
Elastic neutron scattering and transport measurements have been done on the Ni and
Cr equivalently doped iron pnictide BaFe2-2xNixCrxAs2. Compared with the electrondoped BaFe2 − xNixAs2, the long-range antiferromagnetic (AF) order in BaFe2 −
2xNixCrxAs2 is gradually suppressed with vanishing ordered moment and Neel
temperature near x = 0.20 without the appearance of superconductivity. A detailed
analysis on the transport properties of BaFe2−xNixAs2 and BaFe2-2xNixCrxAs2 suggests
that the non-Fermi-liquid behavior associated with the linear resistivity as a function of
temperature may not correspond to the disappearance of the static AF order. From the
temperature dependence of the resistivity in overdoped compounds without static AF
order, we find that the transport properties are actually affected by Cr impurity
scattering, which may induce a metal-to-insulator crossover in highly doped BaFe1.7−
yNi0.3CryAs2.
Reference:
[1] R. Zhang et al., Supercond. Sci. Technol. 27, 115003 (2014)
[2] R. Zhang et al., Phys. Rev. B 91, 094506 (2015)
206
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Nematic Quantum Critical Point in BaFe2-xNixAs2
Zhaoyu Liu1, Yanhong Gu1, Wei Zhang1, Dongliang Gong1, Wenliang Zhang1, Tao Xie1, Xingye
Lu1, Xiaoyan Ma1, Xiaotian Zhang1, Rui Zhang1,2, Jun Zhu1, Cong Ren1, Lei Shan1,3, Xianggang
Qiu1,3, Pengcheng Dai2, Yi-feng Yang1,3, Huiqian Luo1& Shiliang Li1,3
1
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese
2
Department of Physics and Astronomy, Rice University, Houston, Texas 77005-1827, USA
3
The presence of nematic quantum critical point (QCP) in iron-based superconductors
has been widely discussed in recent years. However, most of the studies have been
focused on the under-doped region due to the lack of accuracy in their measurements.
Here we report anisotropic resistivity measurements on BaFe2-xNixAs2using a new
uniaxial pressure device. Our results clearly show the hump feature of nematic
fluctuations in over-doped samples missed by previous reports. By combining the
Curie-Weiss-like behavior of nematic fluctuations in under-doped samples, we identify
the presence of nematic QCP in BaFe2-xNixAs2.
Reference:
[1] J.-H Chu et al.,Science337, 710-712 (2012)
[2] R. M. Fernandes et al.,Nat. Phys. 10, 97-104 (2014)
207
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Critical Charge Fluctuations in Iron Pnictide Superconductors
G. Blumberg1 ,V. Thorsmølle1
1
The multiband nature of iron pnictides gives rise to a rich temperature-doping phase
diagram of competing orders and a plethora of collective phenomena. At low dopings,
the tetragonal-to-orthorhombic structural transition is closely followed by a
concomitant spin density wave transition both being in close proximity to the
superconducting phase. A key question is the microscopic mechanism of high-Tc
superconductivity and its relation to orbital ordering and magnetism.
Here we study the 111 and 122 families of iron superconductors using low energy
polarization resolved Raman spectroscopy. The Raman susceptibility shows critical
non-symmetric charge fluctuations across the entire phase diagram. The charge
fluctuations are interpreted in terms of plasma waves of quadrupole intra-orbital
excitations in which the electron and hole Fermi surfaces breath in-phase. We
demonstrate that above the structural phase transition the quadrupolar fluctuations with
long correlation times are precursor to the discrete four-fold symmetry breaking
transition. This is manifested in the critical slowing down of XY-symmetry collective
fluctuations observed in dynamical Raman susceptibility and strong enhancement of
the static Raman susceptibility. Below superconducting transition, these collective
excitations undergo a metamorphosis into a coherent in-gap collective mode of
extraordinary strength and at the same time serve as glue for non-conventional
superconducting pairing.
We acknowledge collaboration with Z. P. Yin, C. Zhang, S. V. Carr, Pengcheng Dai,
P. Richard, H. Ding, Athena S. Sefat, J. Gillett, S. E. Sebastian, Weilu Zhang, M.
Khodas. Research at Rutgers was supported by US Department of Energy, Office of
Basic Energy Sciences, Division of Materials Sciences and Engineering under Award
DE-SC0005463 and by the National Science Foundation under Awards NSF DMR1104884 and NSF DMR-1405303.
Reference:
[1]V. K. Thorsmølle, M. Khodas, Z. P. Yin, C. Zhang, S. V. Carr, Pengcheng Dai, G.
Blumberg. Critical Charge Fluctuations in Iron Pnictide Superconductors. To appear in
Phys. Rev. B (2016). http://ArXiv.org/abs/1410.6456
208
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As NMR studies on the nematic state in the iron pnictide NaFeAs
Masayuki Toyoda1, Yoshiaki Kobayashi1, Masayuki Itoh1
1
Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Japan
In iron pnictide superconductors, broken symmetries of the electronic state within
the Fe-plane have been discussed in connection with orbital/magnetic orders and
superconductivity. The iron pnictide NaFeAs shows a structural transition at T𝑠 ~50 K
and an antiferromagnetic transition at TN ~40 K, in contrast to BaFe2As2 where the two
transitions occur almost simultaneously. In this study, we have measured the magneticfield direction dependences of 75As-NMR spectra and the nuclear spin-lattice relaxation
rate to study the in-plane anisotropies of the electric field gradient (EFG) and the
magnetic fluctuation at the As-site in NaFeAs. We found that the in-plane anisotropy
of the magnetic fluctuation is enhanced in the temperature (T) range from T𝑠 to TN,
whereas the anisotropy of the EFG slightly increases with decreasing T below Ts. We
discuss the in-plane anisotropies of the electronic state in NaFeAs.
209
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Sign-problem-free quantum Monte Carlo study of high-temperature
superconductors
Zi-Xiang Li1, Fa Wang2,3, Hong Yao1,3and Dung-Hai Lee4,5
1
Institute for Advanced Study, Tsinghua University, Beijing 100084, China.
International Center for Quantum Materials, School of Physics, Peking University, Beijing
100871, China.
3
Collaborative Innovation Center of Quantum Matter, Beijing, China.
4
Department of Physics, University of California, Berkeley, CA 94720, USA.
5
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
2
Superconductivity is an emergent phenomena in the sense that the energy scale
associated with Cooper pairing is generically much lower than the typical kinetic
energy of electrons. Addressing the mechanism of Cooper pairing amounts to determine
the effective interaction that operates at low energies. Deriving such an interaction from
a bottom-up approach has not been possible for any superconductor, especially strongly
correlated ones. Top-down approaches, where one assumes an effective interaction, is
plagued with the difficulty of extracting the implied electronic instabilities without
uncontrolled approximations. These facts severely hinder our ability to determine the
pairing mechanism for high temperature superconductors. Here we perform large-scale
sign-problem-free quantum Monte-Carlo simulations on an effective theory, featured
with antiferromagnetic and nematic fluctuations, to study the intertwined
antiferromagnetic, superconducting, and charge density wave instabilities of the
cuprates. Our results suggest the inclusion of nematic fluctuations is essential in order
to produce the observed type of charge density wave ordering. Interestingly we find
that the d-wave Cooper pairing is enhanced by nematic fluctuations [1].
Single unit cell thick FeSe films grown on SrTiO3 substrate [(FeSe)1/STO] show
superconducting gap and gap closing Tc which are almost an order of magnitude larger
than those of the bulk FeSe. We also study the cooperation between electron-phonon
and pure electron mechanisms of pairing by unbiased sign-problem-free quantum
Monte Carlo computation on effective models capturing the low energy physics of
(FeSe)1/STO. Our results clearly indicate that irrespective to the pure electronic driving
force of Cooper pairing and the resulting pairing symmetry, nematicity and especially
forward-focusing
electron-phonon
couplings
significantly
enhance
the
superconductivity [2].
Reference:
[1] Zi-Xiang Li, Fa Wang, Hong Yao and Dung-Hai Lee, arXiv:1512.04541
[2] Zi-Xiang Li, Fa Wang, Hong Yao and Dung-Hai Lee, arXiv:1512.06179
210
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Direct evidence of nodeless superconductivity and
determination of the superfluid density in single-layer FeSe
grown on STO
Pabitra Kumar Biswas, Zaher Salman, Elvezio Morenzoni, Lei Shu, Donglai Feng
ISIS Pulsed Neutron and Muon Source, GB
Bulk FeSe is superconducting with a critical temperature Tc of 8 K and SrTiO3 is
insulating in nature, yet a Tc as high as 109 K has been reported at the interface between
a single-layer FeSe and SrTiO3 . Elucidating the microscopic properties and
understanding the pairing mechanism of single-layer FeSe is of utmost importance as
it is the basic building block of iron-based superconductors. Angle resolved
photoemission spectroscopy and scanning tunnelling microscopy measurements
observe a gap opening at the Fermi surface below Tc of 60 K. However, these
techniques fall short to give definitive evidence whether the gap is only related to
superconductivity. While transport measurements show zero resistivity, they cannot
confirm superconductivity across the full FeSe/ SrTiO3 interface. Moreover,
determining microscopic length scales such as the magnetic penetration depth and
identifying the symmetry of the superconducting gap remain a key issue. Here, we use
the low-energy muon spin rotation/relaxation technique (LE-µSR) to detect and
quantify the existence of superfluid density and determine the gap symmetry in a singlelayer of FeSe grown on SrTiO3 (100). Our µSR measurements rule out any magnetic
ground state in this system, while the temperature dependent measurements show a
broadening of the field distribution below 65 K. The result is clear indication of the
formation a two dimensional vortex lattice existing over the entire FeSe/ SrTiO3
interface thus providing unambiguous evidence for superconductivity in single-layer
FeSe. From the inhomogeneous field distribution, we determine an effective
penetration depth of λ = 112 nm at T = 0 K. The temperature dependence of the
superfluid density, n𝑠 (T) can be well described by a simple BCS s-wave model,
indicating a nodeless superconducting state with a gap of 10.7(9)meV.
211
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Effects of surface electron doping and substrate on the
superconductivity of epitaxial FeSe films
W. H. Zhang1, T. Zhang1,*, D. L. Feng1
1
State Key Laboratory of Surface Physics, Department of Physics, Fudan University, Shanghai
200433, China
* Email: [email protected]
Recently, surface potassium (K) doping has been shown to be able to enhance the
superconductivity of FeSe films. Here by using scanning tunneling microscopy, we
compare the K doping dependence of the superconductivity in FeSe films grown on
two substrates: SrTiO3 (001) and graphitized SiC (0001). We found that for thick films
(20 unit cells (UC)), the optimized superconducting (SC) gaps are of similar size (~9
meV), regardless of the substrate. However, when the thickness is reduced to a few UC,
the optimized SC gap is increased up to ~15meV for films on SrTiO3 , while it remains
unchanged for films on SiC. This clearly indicate that the FeSe/SrTiO3 interface can
further enhance the superconductivity, beyond merely doping electrons. Moreover, we
found that the further enhancement decays exponentially as the thickness increases
(with a short length scale of 2.4 UC), which is unlikely due to the lattice strain and
suggests the interfacial electron-phonon coupling is the possible origin.
212
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Charge transfer effect of FeSe thin films on SrTiO3
Yuanjun Zhou1 and Andrew J. Millis1
1Department of Physics, Columbia University, New York, NY, USA
Monolayer FeSe grown on SrTiO3 (STO) substrate has shown a significant
enhancement in the superconducting transition temperature (Tc) relative to the bulk
material. Monolayers of FeSe are electron doped relative to bulk; we propose that the
doping comes from work-function-mismatch driven charge transfer from STO impurity
bands, modified by out-of-plane polar distortions of the STO. We present a modified
Schottky model combined with density functional calculations substantiating this
picture for monolyaer FeSe films on Nb doped STO. Physically relevant levels of Nb
doping are shown to lead to doping of the FeSe compatible with observation. Adding
polar fluctuations to the model leads to an electron-phonon interaction whose effect on
the transition temperature is investigated.
YZ is supported by National Science Foundation under grant No. DMR-1120296.
AJM is supported by the Department of Energy under No. DOE-ER-046169.
213
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Unconventional superconducting state in FeSe studied by 77Se-NMR
Anlu Shi1, K. Ishida1, A. Böhmer2, T. Wolf2, C. Meingast2
1
Department of Physics, Graduate School of Science, Kyoto University, Kyoto, Japan
2
Department of Physics, Karlsruhe Institute of Technology, Karlsruhe, Germany
The quantum criticality in iron-based superconductors (FeSCs) has long been
attractive due to the interplay between magnetism and superconductivity, and to the
novel mechanism of unconventional superconductivity. Among them, FeSe shows no
magnetic ordering at ambient pressure, but exhibits a lot of intriguing phenomena such
as an extraordinary enhancement of Tc in thin films[1,2], or recently, the emergence of
a new phase under high magnetic fields[3].
To investigate the superconducting properties of this system, particularly how
unconventional superconductivity in FeSe is suppressed by the external fields, we have
conducted 77Se-NMR (Nuclear Magnetic Resonance) experiments on FeSe single
crystals under different magnetic fields along the c axis. Through the measurements of
the nuclear spin-lattice relaxation rate 1/T1 and spectra analysis, we found the
systematic field dependence of T-variation of 1/T1 above Tc as well as below Tc. We
argue the origin of the field dependence of 1/T1 above Tc from the comparison with
other experimental results obtained in FeSe, and with the field dependence of 1/T1 in
other FeSCs.
Reference:
[1] Q. Wang et al., Chin. Phys. Lett. 29, 037402 (2012)
[2] J. Ge et al., Nat. Mater. 14, 285 (2014)
[3] S. Kasahara et al., PNAS 111, 16309 (2014)
214
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Electronic state and superconductivity in FeSe: A multi-orbital
DMFT study
Jun Ishizuka1, Takemi Yamada1, Yuki Yanagi2, Yoshiaki Ōno1
1
2
Department of Physics, Niigata University, Ikarashi, Niigata 950-2181, Japan
Department of Physics, Faculty of the Science and Technology, Tokyo University of Science,
Noda 278-8510, Japan
The iron-based superconductor [1] has been extensively studied as a complex multiorbital system. Despite the numerous efforts, the origin of their superconducting
mechanism remains unknown.
Recently, the angular resolved photoemission spectroscopy (ARPES) and the
quantum oscillations (QO) study of FeSe single crystals reveal that hole-pocket around
the Γ-point due to the dxy orbital is pushed downward under the Fermi energy. To
address this issue, we investigate a correlation effects on the self-energy, the magnetic
and orbital fluctuations and its derived superconductivity in 16-band d-p model on FeSe
within the dynamical mean-field theory. We find that the dissipation of a shallow holepocket occurs by on-site Coulomb interaction which is corresponding to the orbital
depend band lifting observed by the recent ARPES and the QO experiments [2].
Furthermore, inter-site Coulomb interaction between iron d orbitals and chalcogenides
p orbitals drives an electric orbital order in absence of the low-energy commensurate
spin response. We also calculate the superconducting gap structure in orbital ordered
phase by using the linearized Eliashberg equation, and find that s±-wave pairing is
realized where the dzx(yz) orbital component of spin fluctuation is the cause of
superconductivity.
Reference:
[1] Y. Kamihara et al., J. Am. Chem. Soc. 128 10012 (2006)
[2] M. D. Watson et al., Phys. Rev. B 91 155106 (2015)
215
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A high-pressure magneto-transport study on the FeSe single crystal:
Temperature-pressure phase diagram
J. P. Sun1, G. Z. Ye1, J.-Q. Yan2, B. C. Sales2, J.-G. Cheng1
1
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese
2
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge,
Tennessee 37831, USA
Bulk FeSe superconductor with Tc ≈ 8 K adopts the simplest crystal structure among
the iron-based superconductors [1], yet exhibits the most intriguing physical properties
such as the absence of long-range magnetic order below the tetragonal-orthorhombic
structural transition (nematic order) at Ts ≈ 90 K [2], and the proximity to the crossover
regime between the weak-coupling BCS and strong-coupling BES limits [3]. Moreover,
high Tcs over 40 K can be achieved in FeSe via different routes such as the application
of high pressure [4], the intercalation of molecular spacer layer [5], or the fabrication
of monolayer film on SrTiO3 [6]. The underlying mechanism for the high-Tc
superconductivity remains elusive at present. By employing the magneto-transport
measurements under hydrostatic pressures up to 15 GPa, we have established the most
comprehensive temperature-pressure diagram of FeSe single crystal [7]. Our results
uncovered how the high-Tc superconductivity is achieved in bulk FeSe by revealing
explicitly how the competing orders of nematicity, antiferromagnetism, and
superconductivity evolve under pressure.
Reference:
[1]F. C. Hsu, et al., PNAS 105, 14262 (2008)
[2]J. K. Glasbrenner, et al., Nat. Phys. 11, 953 (2015)
[3]S. Kasahara, et al., PNAS 111,16309 (2014)
[4]S. Medvedev, et al., Nat. Mater. 8, 630 (2009)
[5]M. Burrard-Lucas, et al., Nat. Mater. 12, 15 (2013)
[6]J.-F. Ge, et al., Nat. Mater. 14, 285 (2015).
[7]J. P. Sun, et al., ArXiv1512.06951.
216
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A high-pressure Hall coefficient study on the FeSe single crystal
G. Z. Ye1,J. P. Sun1,J.-Q. Yan2,B.C.Sales2,J.-G. Cheng1
1
Academy of Sciences, Beijing100190,China
2
Materials Science and Technology Division, OakRidge National Laboratory, OakRidge,
At ambient pressure, β -FeSe exhibits a tetragonal-to-orthorhombic structural
transition at Ts≈90K followed by a superconducting transition below Tc≈8K[1].
Upon the application of high pressures, Ts is suppressed gradually and vanishes
completely around P ≈ 2GPa. Meanwhile, a long-range antiferromagnetic order
emergesat Tm≈20K underP~1.5GPa, and displays a dome-shaped Tm(P) with two end
points located at the boundaries separating the three plateaus of Tc(P) [2]. Recent
studies on high-quality FeSe single crystals have characterized its normal state as an
almost compensated semimetal accompanied by an additional Dirac-like electron
pocket [3, 4]. Here, we have measured the Hall coefficient of FeSe single crystal under
hydrostatic pressures up to 8GPa to further characterize the evolution of the normal
state from which the complex T-P phase diagram is derived.
Reference:
[1]F. C.Hsu, et al.,PNAS105, 14262(2008)
[2]J. P. Sun, et al.,ArXiv1512.06951
[3]K. K. Huynh, et al.,PRB90,144516(2014)
[4]M. D. Watson, et al.,PRL115, 027006(2015)
217
Mo-P098
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Optical study of high quality FeSe single crystal
H. P. Wang1, Z. R. Ye2, Y. Zhang2 and N. L. Wang2
1
2
Institute of Physic, Chinese Academy of Sciences, Beijing, China
We perform an in-plane optical spectroscopy measurement on high quality FeSe
single crystals grown by a vapor transport technique. Below the structural transition at
∼90 K, the reflectivity spectrum clearly show an gradual suppression around 450 cm-1
and the conductivity spectrum show a peak at the same frequency. This is a common
feature of gap formation. The scale of energy gap (56 meV) is comparable to the width
of band splitting observed by ARPES (50 meV), so this feature should be associate with
the band splitting effect observed by ARPES. The low-frequency conductivity consist
of two Drude components and the overall plasma frequency is smaller than that of the
FeAs-based compounds, suggesting a lower carrier density or stronger correlation
effect. Similar to iron pnictides, a temperature-induced spectral weight transfer is
observed for FeSe.
218
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Nodal superconductivity in FeS: Evidence from quasiparticle heat
transport
T. P. Ying1, X. F. Lai2, X. C. Hong1, Y. Xu1, L. P. He1, J. Zhang1, M. X. Wang1, Y. J. Yu1, F.
Q. Huang2,3, S. Y. Li1,4
1State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced
Materials, Fudan University, Shanghai 200433, China
2Beijing National Laboratory for Molecular Science and State Key Laboratory of Rare Earth
Materials Chemistry and Applications, College of Chemistry and Molecular Engineering,
Peking University, Beijing 100871, China
3CAS Key Laboratory of Materials for Energy Conversion and State Key Laboratory of High
Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics,
Chinese Academy of Sciences, Shanghai 200050, China
4Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai
200433, China
We report low-temperature heat transport measurements on both single crystal and
flake of iron sulfide FeS with T𝐶 ≈ 5 K, which has the same crystal structure and
similar electronic band structure to the superconducting iron selenide FeSe. In zero
magnetic field, a significant residual linear term κ0/T is observed. At low field, κ0/T
increases rapidly with the increase of field. These results provide strong evidence for
nodal superconducting gap in FeS. The origin of this nodal superconductivity in FeS is
discussed, by comparing with other iron-based superconductors with nodal gap.
Reference:
[1] T. P. Ying et al., arXiv:1511.07717
219
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NMR study on electronic and magnetic properties of Fe-based ladder
compounds AFe2Se3 (A = Ba, Cs)
Kaoru Okada,1 Yoshiaki Kobayashi,1 Masayuki Itoh,1 Yasuyuki Hirata,2 Kazuki
Hashizume,3 Takuya Aoyama,3 Kenya Ohgushi3
1
2
Department of Physics, Nagoya University, Nagoya, Japan
3
Department of Physics, Tohoku University, Sendai, Japan
Fe-based ladder insulating systems AFe2X3 (A= Ba, K, Rb, Cs ; X= S, Se, Te) have
attracted much attention, since superconductivity was recently discovered at high
pressure in BaFe2S3 [1]. One of the systems, CsFe2Se3 (BaFe2Se3), was reported to
have an antiferromagnetic (AFM) phase with the stripe-type (block-type) spin
structure similar to those in parent compounds of Fe-based superconductors below T𝑁
= 175 (255) K [2, 3]. However, the coexistence of the paramagnetic and AFM phases
was observed by the Mössbauer experiment [3] and the hole doping into the Se site
was also discussed from the spectroscopic study on CsFe2Se3 with a formal valence of
Fe2.5+ [4]. In this study, we have made 133Cs and 77Se NMR measurements on single
crystals to investigate the electronic and magnetic properties of CsFe2Se3 and
BaFe2Se3. We observed changes of the 133Cs NMR spectrum at T𝑁 and ~150 K in
CsFe2Se3, indicating that a magnetic transition may take place from incommensurate
to commensurate spin structures at ~150 K. We discuss the spin structures and the
electronic states of both the compounds based on the 133Cs and 77Se NMR results.
References:
[1]H. Takahashi et al., Nat. Mater. 14, 1008 (2015)
[2]Y. Nambu et al., PRB 85, 064413 (2012)
[3]F. Du et al., PRB 85, 214436 (2012)
[4]D. Ootsuki et al., PRB 91, 014505 (2015)
220
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STM study on (Li0.8Fe0.2)OHFeSe single crystal
M. Q. Ren
Department of physics
(Li0.8Fe0.2)OHFeSe is a FeSe-derived bulk superconductor with Tc more than 40K.
Here we report a systematical study of single crystal (Li0.8Fe0.2)OHFeSe by scanning
tunneling microscopy (STM). We observed two kinds of surface terminations, namely
FeSe surface and (Li0.8Fe0.2)OH surface. On the FeSe surface, the superconducting state
is fully gapped with double coherence peaks, and the corresponding magnetic vortex
states are observed. With QPI measurements, we found that besides the scatterings
within the electron pockets at the M points, there are scatterings between states around
Г and M near the Fermi energy. Furthermore, we found that all the QPI features behave
similarly under magnetic field, and only magnetic impurities can induce in-gap states.
These results suggest that (Li0.8Fe0.2)OHFeSe is a robust s-wave superconductor
without sign-changing, even in the presence of Г-M coupling.
221
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Evolution of antiferromagnetic spin fluctuations and superconductivity
in iron-pnictides 𝐋𝐚𝐅𝐞(𝐀𝐬𝟏−𝒙 𝐏𝒙 )(𝐎𝟏−𝒚 𝐅𝒚 )
T. Shiota1, H. Mukuda1, M. Uekubo2, M. Yashima1, F. Engetsu1, K. T. Lai2, Y. Kitaoka1,
S. Miyasaka2, S. Tajima2
1
Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan
2
Graduate School of Science, Osaka University, Osaka 560-0043, Japan
Superconducting(SC) transition temperature (Tc) of LaFe(As1−𝑥 P𝑥 )(O1−𝑦 F𝑦 )
exhibits a nonmonotonic variation with x and y[1], which relates with the
antiferromagnetic (AFM) spin fluctuations(SFs) for y≦0.1[2]. Such unexpected AFM
SFs originates from re-emergent AFM order in x=0.6 of LaFe(As1−𝑥 P𝑥 )O[3,4]. Further
electron-doping by hydrogen-substitution in LaFeAs(O1-yHy) uncovered the presence
of another SC dome and AFM phase[5,6]. To reveal the novel evolution of electronic
states over wide x and y compositions in LaFe(As1−𝑥 P𝑥 )(O1−𝑦 F𝑦 ), we have performed
31
P-NMR study in electron-overdoped samples of y=0.14, LaFe(As1−𝑥 P𝑥 )(O1−𝑦 F𝑦 ).
As a result, we have revealed that Tc value is markedly enhanced from x=0 to x=0.4 in
association with the remarkable enhancement of AFMSFs, as well as in the previous
results[2]. However, we unraveled that the characteristic of AFMSFs gradually vary
from y=0 to y=0.14: the AFMSFs for y=0 develop rapidly at low temperature whereas
the latter does gradually upon cooling from higher temperature. According to the
theoretical study[7], such characteristics of AFMSFs may be attributed to the evolution
of orbital dependent AFMSFs, that is, AFMSFs mainly derives from d(xz,yz) orbits at
y=0 to that from d(xy) orbit at y=0.14.
Reference:
[1] K. T. Lai et al., Phys. Rev. B 90, 064504 (2014).
[2] H. Mukuda et al., Phys. Rev. B 89, 064511 (2014).
[3] S. Kitagawa et al., J. Phys. Soc. Jpn 83, 023707 (2014) .
[4] H. Mukuda et al., J. Phys. Soc. Jpn. 83, 083702 (2014).
[5] S. Iimura et al., Nat. Commun. 3, 943 (2012).
[6] M. Hiraishi et al., Nat. Phys. 10, 300 (2014).
[7] H. Usui et al., Sci. Rep. 5, 11399 (2015).
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Searching for a general trend of orbital differentiation
tuning in FeAs-based superconductors
Matheus Radaelli1, Mario Moda Piva1, Camilo Bruno Ramos de Jesus1 , Guilherme Gorgen
Lesseux1 , Dina Tobia1 , Ricardo Rodrigues Urbano1 , Pascoal G. Pagliuso1
1
Universidade Estadual de Campinase-mail: [email protected]
FeAs-based superconductors are an interesting playground to understand the
interplay between superconductivity and magnetism. The tuning of a Spin Density
Wave (SDW) phase to lower temperatures seems to play an important role in the
emergence of superconductivity in these classes of compounds. So to further
understand the microscopic mechanism of such suppression can shed some light on the
pairing mechanism of these superconductors.
Previous reports concerning studies of spin dynamics by Electron Spin Resonance
(ESR) technique in Ba1-xEuxFe2As2 and Ba1Fe2-x(Cu,Mn)xAs2 [1-2] provide evidence
for the role of the Fe 3d bands orbital differentiation in the suppression of the
antiferromagnetic SDW phase in this class of materials [2].
Therefore, in these work, we will discuss how this interpretation can be extended to
Sr1-xEuxFe2As2 and Sr1Fe2-x(Cu,Mn)xAs2. To achieve our goal we have performed xray powder diffraction, elemental analysis (EDS, WDS), resistivity, magnetization,
magnetic susceptibility DC and specific heat measurements on In-flux grown [3] single
crystals of these compounds.
Reference:
[1] Rosa P F S et al. 2014 Sci. Rep. 4 6543;
[2] Rosa P F S et al. 2012 PRB 86, 16513;
[3] Garitezi T M et al. 2013 Braz. J. Phys. 43 223;
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BiS2 Superconductors: an Ab-Initio Panorama
Corentin Morice,1 Emilio Artacho,1 3 Sian E. Dutton,1 Ryosuke Akashi,4 Ryotaro Arita,5
Daniel Molnar,1 Hyeong-Jin Kim1 and Siddharth S. Saxena1
1
Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
2
Nanogune and DIPC, Tolosa Hiribidea 76, 20018 San Sebastian,´Spain
3
Basque Foundation for Science, Ikerbasque, 48011 Bilbao, Spain
4
Department of Physics, University of Tokyo, Tokyo, Japan
5
RIKEN, Wako, Saitama 351-0198, Japan
The discovery of superconductivity in Bi4 O4 S3 , quickly followed by the one in
La(O, F)BiS2 , opened up a new research field on novel BiS2 superconductors. The two
main series of compounds studied so far are Bi3O2S3 and LnO𝑥 F1−𝑥 BiS2 . We studied
these two series of compounds using density functional theory. Our results demonstrate
that in Bi3 O2 S3 , the S2 layers dope the BiS2 bands, and that the conduction electrons
are accumulated in the BiS planes, not the full BiS2 layer. We find that CeO0.5 F0.5 BiS2
has a ferromagnetic tendency, confirming experimental results, but also that it is very
close to an instability towards a phase with weak antiferromagnetic coupling. We show
that PrO0.5 F0.5 BiS2 has a strong tendency for magnetic order, which can be
ferromagnetic or antiferromagnetic depending on subtle differences in 4f orbital
occupations. We demonstrate NdO0.5 F0.5 BiS2 has a stable magnetic ground state with
weak tendency to order. We show that the change of rare earth does not affect the Fermi
surface, and predict that CeOBiS2 should display a pressure induced phase transition
to a metallic, if not superconducting, phase under pressure. Finally, we discuss the
possibility of charge density wave instability and estimate the superconducting
transition temperature of LaO0:5F0:5BiS2 using first-principles techniques.
Reference:
[1] Corentin Morice, Emilio Artacho, Sian E. Dutton, Daniel Molnar, HyeongJin Kim and Siddharth S. Saxena, Effects of stoichiometric doping in
superconducting Bi-O-S compounds, J. Phys.: Condens. Matter 27 (2015)
135501
[2] Corentin Morice, Emilio Artacho, Sian E. Dutton, Daniel Molnar, Hyeong-Jin
Kim and Siddharth S. Saxena, Electronic and magnetic properties of
superconducting LnO1 xFxBiS2 (Ln = La, Ce, Pr, and Nd) from first principles,
arXiv:1312.2615
224
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Superconductivity and Eu Valence Instability in Undoped
Eu3Bi2S4F4
Huifei Zhai
-abstractWe recently synthesized a novel bismuth sulfofluoride, EuBiSF2,[1] a CDW-like
transition occurs at 280 K, below which SC emerges at 0.3 K. The Eu ions show an
anomalously mixed valence about +2.2. With structural design, we successfully
synthesized a new europium bismuth sulfofluoride, Eu3Bi2S4F4.[2] The compound
crystallizes in a tetragonal lattice (space group I4/mmm, a = 4.0771(1) Å, c = 32.4330(6)
Å, and Z = 2), in which CaF2-type Eu3F4 layers and NaCl-like BiS2 bilayers stack
alternately along the crystallographic caxis. There are two crystallographically distinct
Eu sites, Eu(1) and Eu(2) at the Wyckoff positions 4e and 2a, respectively. Our bond
valence sum calculation, based on the refined structural data, indicates that Eu(1) is
essentially divalent, while Eu(2) has an average valence of +2.64(5). This anomalous
Eu valence state is further confirmed and supported, respectively, by Mössbauer and
magnetization measurements. The Eu3+ components donate electrons into the
conduction bands that are mainly composed of Bi 6px and 6py states. Consequently,
the material itself shows metallic conduction and superconducts at 1.5 K without
extrinsic chemical doping.
[1] Hui-Fei Zhaiet al.,Phys. Rev. B90, 064518 (2014).
[2] Hui-Fei Zhaiet al.. J. Am. Chem. Soc. 2014, 136, 15386 −15393.
225
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Superconductivity in the heavy electron Ni-Chalcogenide,
TlNi2Se2
E.Jellyman1, Dr E. Blackburn1, R. Riyat1, Prof. E. M. Forgan1 and Dr M. Fang2
1.
School of Physics and Astronomy, University of Birmingham, B15 2TT, United Kingdom
2.
TlNi2Se2 is a Type-II heavy-electron superconductor with a tetragonal structure and
no structural transitions below 300K. TlNi2Se2 becomes superconducting at Tc = 3.7 K
with an upper critical field of Hc2 = 0.802 T. Previous results by Want et al. [1] and
Hong et al. [2] demonstrate a heavy electron mass of m* = (14 – 20)me. In [1] the
material was fitted by a BCS two-gap model with a smaller superconducting gap
predicted in [2] to be fully suppressed at ~ 0.29 T. An investigation into the flux lines
of TlNi2Se2 was conducted at the Paul Scherrer Institute (PSI) using small-angle
neutron scattering in order to probe the change in the form factor (FF) of the flux lines
with respect to field changes at a fixed temperature of 0.1K. This kind of investigation
is useful for characterising the superconductor as it can lead to an accurate
measurement of the penetration depth of the superconductor as well as reveal any Paulilimiting [3] or anisotropic flux lattice (FL) behaviour. From this we can make
comparisons to other known and characterised superconductors.
So far some measurements have been gathered from PSI on SANS-I at four fields
from 0.2 T to 0.6T at 0.1K. These measurements show a rapid drop in FF for the FL
above 0.2 T and then an increase in FF above 0.4 T. If this increase is persistent up to
higher fields this could be evidence of Pauli limiting. The drop above 0.2T, which
becomes much more obvious above 0.3T, is likely indicative of the suppression of the
smaller superconducting gap at 0.29T, which creates a drop in the superfluid density of
the Cooper pairs and an increase in the penetration depth. There is also an observed
rotation of the domains with respect to each other and field strength. However no
conclusions have yet been drawn regarding this and more study is required of the
material.
Reference:
[1] Hong et al. PRB 90, 060504(2014)
[2] Wang et al. PRL 111, 207001(2013)
[3] Zocco et al. PRL 111, 057007 (2013)
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Electronic structure of the titanium-based oxypnictide
superconductor Ba0.95Na0.05Ti2Sb2O and direct observation of its
charge density wave order
Q. Song
Department of physics
The unconventional superconducting ground state usually emerges in proximity to a
spin or charge ordering state, such as that in cuprates, iron-based superconductors and
layered chalcogenides. This unique character offers a platform for searching
unconventional superconductivity in analogous layered compounds. Recently,
superconductivity has been achieved in Ba1-xNaxTi2Sb2O with maximum Tc at 5.5 K,
which makes this material more interesting[1]. Here we perform high resolution angleresolved photoemission spectroscopy and scanning tunneling microscopy studies on the
titanium-based oxypnictide superconductor Ba0.95Na0.05Ti2Sb2O. The electronic
structure shows both multi-orbital and three-dimensional nature, consistent with the
theoretical calculations. The observed Fermi surface is well nested along the (π,π)
direction, which might probably be the driving for ce of the CDW transition. This is
further proved by the scanning tunneling microscopy result, which directly observed a
CDW wave vector at (π,π) direction. However, due to the weak CDW coupling, we
didn’t observe the CDW gap here. Our results give a comprehensive picture of the
electronic structure and direct observation of the CDW order in Ba0.95Na0.05Ti2Sb2
227
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X-ray PhotoEmission and Absorption Study of the Bismuth Oxide
Family
Shadi Balandeh1,Robert Green1,Kateryna Foyevtsova1,Shun Chi1,George A.Sawatzky1
1
The University of British Columbia, Vancouver, BC, Canada
Electronic structures of the both pure barium bismuth oxide semiconductor and the
potassium substituted superconducting single crystals have been studies with the x-ray
photoemission and absorption techniques at Canadian Light Source and described by
Density Functional Theory and Configuration Interaction Cluster calculations.
The results reveal new information on the material’s properties and the importance
of the ligand oxygens involved.
Reference:
[1] Kateryna Foyevtsova et al. PHYSICAL REVIEW B 91, 121114(R) (2015)
228
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Specific heat and electrical resistivity at magnetic fields in
antiferromagnetic heavy fermion CeAl2
T. Ebihara1, M. Tsuchiya1, Y. Saitoh, J. Jatmika1, M. Tsujimoto2, Y. Shimura2, Y. Matsumoto2, S.
Nakatsuji2
1
2
Departmnet of Physics, Shizuoka University, Shizuoika, Japan
Institute for Solid State Physics, The University of Tokyo , Chiba, Japan
CeAl2 is a prototype heavy fermion compound ordering antiferromagnetically at 4
K. Below TN, the Sommerfeld coefficient (γ) is 135 mJ/K2mol, which is 10 times larger
than that of corresponding material LaAl2.[1] The Fermi surfaces are well clarified
using de Haas-van Alphen effect above metamagnetic transition at 5 T. In field induced
ferromagnetic state, Fermi surface of CeAl2 is closely similar to that of LaAl2. The
effective masses (m*s) of CeAl2 are in a range from 1 to 17 me, thus m* is enhanced
comparing to that of LaAl2. [2] The mass enhancement values range 5 to 10. Although
specific heat was measured at magnetic fields up to 5 T, specific heat measurements
were not performed in field induced ferromagnetic state. Because specific heat
measurement is absent above critical field, we have not been possible to directly
compare the effective mass to γ in CeAl2 above critical field.
We measured specific heat and electrical resistivity as a function of magnetic field
up to 8 T. At the metamagnetic transition around 5 T, γ reduces to 80~100 mJ/K2mol.
We also determined the slope A of ρ~ AT2 to compare γ. The field dependence of slope
A is similar to that of γ. These results imply γ above 5 T explains mass enhancement
above 5 T and there exists magnetically insensitive contribution to enhancement of γ in
CeAl2.
Reference:
[1] C. D. Bredlet al., Z. Phys, B 29, 327 (1978)
[2] P. H. P Reindeers and M. Springford, J. Mag. Mag. Mat. 79, 295 (1989)
229
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Single Crystal Growth and Magnetism of New Compounds
RRh2Cd20 (R : rare earth metals)
Y. Hirose1, H. Doto2. T. Kawano2, F. Honda3, A. Miyake4, M. Tokunaga4, R. Settai1
1
Department of Physics, Niigata University, Niigata 950-2181, Japan
Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan
3
4
The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581,Japan
2
RT2X20 (R: rare earth metals, T: transition metals, X: Al, Zn) crystallizes in the cubic
CeCr2Al20 type structure. In this system, some interesting phenomena are reported such
as super heavy-fermion state in YbCo2Zn20 and the coexistence of the quadrupolar
ordering and superconductivity in PrTi2Al20 and PrIr2Zn20[1,2,3].
We succeeded in growing new compounds RRh2Cd20 (R = La, Ce, Pr, Sm) by the Cd
self- flux method. The crystal structure is found to be the cubic CeCr2Al20 type by the
powder X-ray diffraction technique. We measured the electrical resistivity, magnetic
properties, and specific heat. The electrical resistivity of SmRh2Cd20 indicates an abrupt
decrease at 3 K, corresponding to a magnetic transition. Except for SmRh2Cd20,
RRh2Cd20 shows no anomalies down to 0.8 K in the resistivity.
Reference:
[1] M.S. Torikachvili et al., PNAS 104, 9960 (2007).
[2] A. Sakai et al., J. Phys. Soc. Jpn. 81, 083702 (2012).
[3] T. Onimaru et al., PRL 106, 177001 (2011).
230
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Magnetic Order and Heavy Fermion Behavior in Caged Compound
Ce3Ru4Sn13
Jiahao Zhang1, Sile Hu1, Hongji Shi1, Hengcan Zhao1, Frank Steglich2, Peijie Sun1
1
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics,Chinese
2
We have for the first time successfully synthesized the single crystal Ce3Ru4Sn13 and
measured the magnetic, thermodynamic and transport properties. Combined specific
heat and magnetic measurements show that Ce3Ru4Sn13 is a heavy fermion compound
with a low Kondo temperature of about 3K, below which an antiferromagnetic ordering
also emerges. The low-temperature thermodynamic properties are determined by
competition among crystal field effect, Kondo effect and magnetic correlation, all of
which are of similar energy scale. Specific heat and electrical resistivity measurements
in magnetic field indicate a field induced quantum phase transition at around 8T.
Reference:
A. Ślebarski et al, Journal of Alloys and Compound 615 (2014) 921-928
231
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Vibron states in tetragonal Ce-based intermetallic compounds
M. Klicpera1,2, M. Boehm2, P. Čermák3, P. Javorský1
1Charles University in Prague, Faculty of Mathematics and Physics, Department of Condensed
Matter Physics, KeKarlovu 5, 121 16 Prague 2, Czech Republic
2Institut Laue-Langevin, 71 avenue des Martyrs - CS 20156, 38042 Grenoble Cedex 9, France
3Jülich Centre for Neutron Science JCNS, ForschungszentrumJülich GmbH, Outstation at MLZ,
Lichtenbergstraße 1, 85747 Garching, Germany.
CeTX3 and CeT2X2 compounds, where T is a transition element d-metal and X a pmetal, form a relatively large family of tetragonal intermetallics with a variety of
interesting electronic properties. The electronic ground state in these compounds
strongly depends on the competition between the RKKY and Kondo interaction, but
also on the influence of the crystal electric field (CF) on the single 4f electron of Ce3+.
Both CeCuAl3 and CePd2Al2 order antiferromagnetically below 2.7 K adopting
amplitude modulated magnetic structures with magnetic moments confined within the
basal plane. The inelastic neutron scattering spectra of these compounds show three
CF-like (magnetic) peaks, while only two CF excitations are expected for Ce-based
compounds. Moreover, the first CF excitation in CePd2Al2 is shifted to higher energy
due to a structural transition to an orthorhombic structure, while the other two
excitations remain untouched. We interpret these results as experimental evidence for
a vibron quasi-bound state [1,2], due to strong interactions between crystal field
excitations and phonons.
Reference:
[1] D. T. Adroja, A. del Moral et al., Phys. Rev. Lett., 108, 216402 (2012).
[2] L.C. Chapon, E.A. Goremychkin, et al., Physica B 378-380, 819 (2006).
232
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Low-temperature STM/STS study of heavy fermion system CeB6
Yasuo Yoshida1, Howon Kim1, Masahiro Haze1, Yoshinori Miyata1, Hiroyuki
Suzuki1,2, Fumitoshi Iga3,4, Yukio Hasegawa1
1
Institute for solid state physics, University of Tokyo, Kashiwa,Japan
2
National Institute for Material Science, Tsukuba, Japan
3
Graduate school of engineering and science, University of Ibaraki, Ibaraki,Japan
4
Collage of Science, University of Ibaraki, Ibaraki, Japan
We conducted scanning tunneling microscopy and spectroscopy measurements at
low temperatures and in magnetic fields to investigate the (001) surface of the heavy
fermion compound CeB6. By cleaving the sample in ultrahigh vacuum and at room
temperatures, we obtained flat and wide terraces separated by an atomic size step. We
observed various types of reconstructed and non-reconstructed surfaces, which are
similar to ones observed on cleaved surfaces of SmB6 [1, 2]. The reconstructed surfaces
have strong bias-voltage dependence indicating the semiconducting characters of the
surfaces. We also observed a Fano-like peak structure in the tunnel spectra of the nonreconstructed Ce-terminated surface as expected for Kondo systems. We will report the
details of the experimental results in the presentation.
Reference:
[1] S. Rossler et al., Proc. Natl. Acad. Sci. USA 111, 4798 (2014).
[2] W. Ruan et al., Phys. Rev. Lett. 112, 136401 (2014).
233
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Structural, Thermodynamic and Electrical Transport Properties of a
Novel Cerium Gallide CeRh2Ga2
D. Gnida1, S. Nesterenko2, A. Tursina2, V. Avzuragova2, D. Kaczorowski1
1Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O.B. 1410,
50-950 Wrocław, Poland
2Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia
The formation of a novel ternary compound CeRh2Ga2 was established in the course
of our investigation of the phase equilibria in the Ce-Rh-Ga system. Its crystal structure
at room temperature was determined from the single-crystal X-ray diffraction data to
be of the CaBe2Ge2-type. The refined value of the tetragonal lattice parameters ratio c/a
implies a possible instability towards a lower symmetry structure. Indeed, the structural
phase transition occurs at Ts = 265 K, and manifests itself as distinct anomalies in the
temperature variations of the heat capacity and the electrical resistivity. Below Ts, the
compound exhibits unusual behavior of the electrical transport with a non-monotonous
rise of the resistivity with decreasing temperature. At Tm = 1 K, both C(T) and (T)
show maxima of magnetic origin. Above Tm, CeRh2Ga2 is a Curie-Weiss paramagnet
with fairly stable 4f electronic shell. The thermodynamic and electrical transport data
concomitantly indicate a heavy-fermion character of the compound studied.
234
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A novel hybridized crystal field - phonon excitation in the noncentrosymmetric heavy fermion compound CeAuAl3
Petr Čermák1, Astrid Schneidewind1, Christian Franz2,3, Rudolf Schönmann2, Oleg Sobolev2,4, and
Christian Pfleiderer2
1
Jülich Centre for Neutron Science, MLZ, Garching, DE
Physik-Department, TechnischeUniversitätMünchen, Garching, DE
3
FRM II, TechnischeUniversitätMünchen, Garching, DE
4
Institute for Physical Chemistry, Georg-August-University, Göttingen, DE
2
Hybridized excitations that comprise of well-understood collective modes have
received increasing interest as the possible origin of unconventional materials
properties and novel functionalities. In strongly correlated electron systems the effects
of electron-phonon interactions are typically neglected, being deemed not important for
an overall understanding. However, recently neutron time-of-flight spectroscopy on
polycrystalline CeCuAl3 have provided putative evidence for a vibron, i.e., a combined
crystal field – optical phonon excitation [1], whereas no such excitation could be
detected in the isostructural sister compound CeAuAl3 [2]. This raises the question to
what extent such hybrid modes represent a generic property of the series of CeTAl3
compounds (T: transition metal element) or even f-electron systems in general. To
pursue this question we have revisited the properties of CeAuAl3 using triple axis
neutron spectroscopy on a float-zoned high-quality single-crystal. In contrast with early
conjectures, we find two pieces of strong evidence suggesting strong crystal field –
phonon interactions and the formation of a novel hybrid mode. First, at the zone center
there is clearly a hybridized excitation between the crystal-field and phonons, which
appears to be in general agreement with vibronic bound state reported for CeCuAl3 [1].
However, in our single-crystal study of CeAuAl3 we can clearly attribute this mode to
the interaction of the crystal field with acoustic phonons at the zone boundary. Second,
we observe a distinct anticrossing of the transverse acoustic phonon with the Γ7(1)
crystal field level. To the best of our knowledge such an anti-crossing has not been
reported before. Both phenomena are in agreement with observed dominant phonon
scattering processes by the localized 4f electrons [3]. Taken together, our results
suggest that strongly hybridized crystal field – phonon excitations may, in fact, be
rather common in f-electron compounds.
References:
[1] D.T. Adroja, A. Moral, C. Fuente, A. Fraile, E. A. Goremychkin, J. W. Taylor, A.
D. Hillier, and F. Fernandez-Alons, Phys. Rev. Lett. 108, 216402 (2012).
[2] D.T. Adroja, C. de la Fuente, A. Fraile, A. D. Hillier, A. Daoud-Aladine, W.
Kockelmann, J. W. Taylor, M. M. Koza, E. Burzurí, F. Luis, J. I. Arnaudas, and A.
Moral, Phys. Rev. B 91, 134425 (2015).
[3] Y. Aoki, M. A. Chernikov, H. R. Ott, H. Sugawara, and H. Sato, Phys. Rev. B 62,
87 (2000).
235
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Ce-based Antiferromagnetic Compound CePd2Ga Probed by Ga-NMR
Y. Kishimoto1, H. Kotegawa1, H. Tou1, E. Matsuoka1, and H. Sugawara1
1
Department of Physics, Graduate School of Science, Kobe University, Kobe 657-8501, Japan
Cerium-based compound CePd2Ga (space group: Pnma, No.62) is known to show
an antiferromagnetic ordering at TN~3 K, from electric resistivity, magnetic
susceptibility and heat capacity measurements [1]. However, microscopic
measurements such as nuclear magnetic resonance (NMR) and nuclear quadrupole
resonance (NQR) have not been done. In order to investigate magnetic properties of
CePd2Ga, we have tried to prepare high quality single crystals. Single crystals used in
this studies were grown by Czochralski method and annealed at several different
conditions to reveal an effect of annealing. From the results of ac resistivity
measurements, the effect of annealing will be discussed. Furthermore, we carried out
Ga-NMR for this single crystal in order to investigate the physical properties from a
microscopic view points.
Reference:
[1] K. Terayama et al., J. Phys: Condense. matter7 6899 (1995).
236
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Kondo behavior in antiferromagnetic CePt3P
J. Chen,1 Z. Wang,1 S. Y. Zheng,1 Z. X. Shen,1 C. M. Feng,1 Z.A.Xu1,2
1
2
Department of Physics, Zhejiang University, Hangzhou 310027, China
Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
CePt3P, crystallizing in an antiperovskite-based tetragonal structure, which is closely
related to that of the heavy fermion superconductor CePt3Si [1], was first synthesized
and the physical property was studied by means of magnetization, electrical resistivity,
magnetoresistivity and specific heat measurements. Different from the other candidates
in the family of APt3P (A = Sr, Ca, La) which show superconductivity [2,3], CePt3P
orders antiferromagnetically at TN = 3.0 K due to the presence of well localized Ce-4f
magnetic moments which are partly screened via a Kondo mechanism. The electrical
behavior is governed by the interplay between the Ruderman-Kittel-Kasuya-Yosida
and Kondo interactions and modified by crystalline electric field effect [4,5]. The
Kondo temperature is of same order of magnitude as TN. A magnetic-field-induced
spin-flop transition was observed below TN. A huge frustration parameter f = Θw/TN is
observed. The Sommerfeld coefficient of electronic specific heat exhibits some
enhancement with γ = 86 mJ/mol·K2 indicating the formation of moderate-heavy
quasiparticles in the antiferromagnetic state. Based on the variation of the physical
properties with magnetic field, the magnetic phase diagram has been constructed, which
needs further verification, e.g., by neutron diffraction or Mössbauer spectroscopy.
References:
[1] E. Bauer, G. Hilscher, H. Michor, Ch. Paul, E.W. Scheidt, A. Gribanov, Yu. Seropegin, H.
Noël, M. Sigrist, and P. Rogl, Phys. Rev. Lett. 92(2), 027003 (2004).
[2] T. Takayama, K. Kuwano, D. Hirai, Y. Katsura, A. Yamamoto, and H. Takagi, Phys. Rev.
Lett. 108, 237001 (2012).
[3] H. Chen, X. F. Xu, C. Cao, and J. H. Dai, Phys. Rev. B 86, 125116 (2012).
[4] F. Steglich, J. Arndt, O. Stockert, S. Friedemann, M. Brando, C. Klingner, C. Krellner, C.
Geibel, S. Wirth, S. Kirchner, and Q. Si, J. Phys.: Cond. Matt. 24, 294201 (2012).
[5] Q. Si, F. Steglich. Science, 329 (5996), 1161-1166 (2010).
237
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Development of in-gap states in the antiferromagnetic Kondo
semiconductor CeOs2Al10 by doping of 5d electrons and holes
J. Kawabata1, T. Ekino2, Y. Yamada1, A. Sugimoto2, Y. Muro4, T. Takabatake1,3
1
Graduate School of Advanced Sciences of Matter,
Graduate School of Integrated Arts and Sciences
3
Inst. for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima, Japan
4
Faculty of Engineering, Toyama Prefectural University, Izumi, Japan
2
The Kondo semiconductor CeOs2Al10 exhibits an antiferromagnetic (AFM) order at
rather high temperature TN = 28.5 K [1,2]. On cooling, a hybridization gap V1 = 400
mV, an AFM gap VAF = 200 mV, and another hybridization gap V2 = 100 mV
successively open in the density of states, as observed by the break junction technique
[3]. The 5d hole and electron doping in Ce(Os1-yRey)2Al10 and Ce(Os1-xIrx)2Al10 result
in the asymmetric decrease of TN in the phase diagram [4]. Here, we report on the
tunneling study of these systems. The tunneling spectra dI/dVs show the development
of in-gap states at the Fermi level in concomitant with the disappearance of V2. By the
5d hole doping, both V1 and VAF decrease for y≤ 0.02 and disappear at y = 0.05.
However, for 5d electron doping at high level x = 0.15, the two gaps still exist together
with the diminished TN = 7K. These facts indicate that the presence of the hybridization
gap V1 is necessary for the AFM order in CeOs2Al10.
Reference:
[1] T. Nishiokaet al., JPSJ 78，123705，2009.
[2] Y. Muroet al., PRB 81，214401，2010.
[3] J. Kawabata et al., PRB 92, 201113(R), 2015.
[4] J. Kawabata et al., PRB 89, 094404, 2015
238
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Uniaxial pressure effects on the unusual antiferromagnetic transition
in the Kondo semiconductor CeOs2Al10
K. Hayahsi1, K. Umeo2, Y. Yamada1, J. Kawabata1, Y. Muro4, T. Takabatake1.3
1
AdSM, 2N-BARD, 3IAMR, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
4
Faculty of Engineering, Toyama Prefectural University, Imizu 939-0398, Japan
The orthorhombic Kondo semiconductor CeOs2Al10 exhibits strong magnetic
anisotropy (a>c>b) and undergoes an unusual antiferromagnetic (AFM) order at TN=
28.5 K, higher than those in ROs2Al10 (R = Pr, Nd, Sm, and Gd) [1,2]. In order to reveal
the relation between the c-f hybridization and the AFM order, we have measured the
magnetic susceptibility (B // P) and specific heat under uniaxial pressures up to 0.3 GPa
applied along the principal axes. For P // a and P // c, the peak temperatures of a(T) and
c(T), respectively, shift to higher temperatures, while TN hardly changes. On the
contrary, TN increases up to 30 K for P // b with the expansion of the lattice in the a-c
plane. The contrasting effects suggest that the increasing TN under P // b originates in
the suppression of hybridization in the a-c plane. This fact supports the argument that
the unusual AFM order in CeOs2Al10 is caused by the strong c-f hybridization in the ac plane.
References
[1] T. Nishioka et al., J. Phys. Soc. Jpn. 78, (2009) 123705.
[2] Y. Muro et al., J. Phys. Soc. Jpn. 80, (2011) SA021.
239
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Semiconducting behaviour of Ce3Cu3Sb4 revisited
Jerzy Goraus1, Piotr Witas1, Andrzej Ślebarski1, Marcin Fijałkowski1, Lech Kalinowski1
1
Institute of Physics, University of Silesia, 40-007 Katowice, Poland
We present the studies involving band structure calculations and experimental
characterization of Ce3Cu3Sb4 compound, as well as the Ce3Cu3-x NixSb4 series where
Cu atom was substituted by its neighbor Ni in periodic system. Ce3Cu3Sb4 was
previously reported as ferromagnetic semiconductor [1] or semimetal with significant
thermopower at room temperature [2]. Basing on our calculations, we show that it has
some residual density of states at the Fermi level and relatively broad band gap just
below Fermi level. We present calculations performed within virtual crystal
approximation which simulate the doping and the vacancies as well as the calculations
for the reduced unit cell which simulate the effect of hydrostatic pressure onto the
bandgap in the density of states. We show that 4f electron correlations have tremendous
influence on the shape and location of band-gap. The calculations also show the shift
of the bandgap in respect to the Fermi level as a result of external pressure or change
of the stoichiometry. In consequence of the change of these parameters, Ce3Cu3Sb4
would became a unique wide bandgap Ce based semiconductor. We also present
thermopower, thermal conductivity, resistivity, Hall effect, and magnetic results
obtained for the system Ce3Cu3-x NixSb4. Thermoelectric figure of merit reaches value
ZT ~ 0.3 at 350 K for Ce3Cu2.75Ni0.25Sb4, which qualifies these materials for
thermoelectric applications.
Reference:
[1] S. Patil, Z. Hossain, P.L. Paulose, R. Nagarajan, L.C. Gupta, C. Goddard,
Solid State Commun. 99 (1996) 419.
[2] P. Wachter, L. Degiorgi, G. Wetzel, H. Schwer, Phys. Rev. B 60 (1999) 9518.
240
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Scaling behavior of the temperature dependent thermopower in
CeAu2Si2 under pressure
Z. Ren1, G. W. Scheerer1, G. Lapertot2, D. Jaccard1
1
DQMP-University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland
2
SPSMS, UMR-E CEA/UJF-Grenoble 1, INAC, Grenoble, F-38054, France
In addition to hosting pressure-induced superconductivity [1], CeAu2Si2 also offers
us a rare opportunity to extensively study unusual features in thermopower from weak
Kondo to intermediate valence regime in a single compound due to its large PC ~ 22GPa.
Here we present the results of thermopower and resistivity measurements on highquality CeAu2Si2 crystals at temperatures down to 1.3 K and pressures up to 27.8 GPa.
It is found that, over a broad pressure range below PC, the normalized thermopower
above a certain temperature T* can be scaled to a universal function f(T/T*). By
comparing with resistivity results, we show that the normalization factorand T* are
essentially governed by the Kondo coupling and crystal-field splitting, respectively.
Below T*, signatures of the Kondo and crystal-field effects are also observed. These
results establish thermopower as a useful probe of high-temperature energy scales in
Ce-based Kondo lattice systems under pressure.
Reference:
[1] Z. Ren et al., PRX 4, 031005 (2014).
241
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ARPES and XAS Study of the Fermi surface reconstruction in
the f-electron Charge Density System of RTe2 and RTe3
(R=Ce, Pr)
J.-S. Kang1, Eunsook Lee1, D. H. Kim1, Hyun Woo Kim1, J. D. Denlinger2, B. H.
Min3, Y. S. Kwon3, Heejung Kim4, Junwon Kim4, Kyoo Kim4, B. I. Min4
1
Department of Physics, The Catholic University of Korea, Bucheon 420-743, Korea
Advanced Light Source (ALS), Lawrence Berkeley Laboratory, Berkeley, CA. 12345
3
Department of Emerging Materials Science, DGIST, Daegu 711-873, Korea
4
Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
2
The electronic structures of quasi-two dimensional f-electron charge-density-wave
(CDW) systems of RTe2 and RTe3 (R=Ce, Pr) have been investigated by employing
angle-resolved photoemission spectroscopy (ARPES) and soft X-ray absorption
spectroscopy (XAS) experiment and first-principles band structure calculations. R 3d
XAS spectra indicate that Ce and Pr ions are trivalent in RTe2 and RTe3. In the
measured Fermi surface (FS) of CeTe2, the zigzag features having the four-fold
rotational symmetry are observed near the X point, which can be described as the
CDW-induced FS reconstruction due to the 4x4 CDW supercell structure [1,2]. In
contrast, the two-fold symmetric features are observed in the measured FS of PrTe3, in
agreement with the calculated FS for the assumed 7x1 CDW supercell structure. The
metallic states crossing the Fermi level (EF) are observed in ARPES even in the CDW
states, indicating that the metallic states remain under the CDW transition with the
remnant ungapped FSs. The shadow bands and the corresponding very weak FSs are
observed in the CDW states, which arise from the band folding due to the interaction
of Te sheets and R-Te layers and also due to the CDW-induced FS reconstruction. The
photon-energy maps for the Fermi-level states exhibit the straight vertical dispersions,
which demonstrates the dominant two-dimensional character in RTe2 and RTe3 (R=Ce,
Pr).
Reference:
[1] J.-S. Kang, et al., Phy. Rev. B 85, 085104 (2012).
[2] Eunsook Lee, et al., Phy. Rev. B 91, 125137 (2015).
242
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Possible Ferromagnetic Quantum Critical Point in CeSi1.82 Under
Pressure
C. Y. Guo1, B. Shen1, Y. F. Wang1, Y. H. Chen1, W. B. Jiang1, Y. Chen1 , X. Lu1 , H. Q. Yuan1
1Center for Correlated Matter and department of Physics, Zhejiang University, Hangzhou, China
The ferromagnetic quantum phase transition has attracted enormously attentions in
recent years. Except the transition metal compounds, there are also a lot of interesting
kondo lattice compounds that have been studied. But except for YbNi4(P1-xAsx)2[1], in
most of the cases, instead of quantum critical points at zero temperature, the tricritical
points happen at non-zero temperatures seem to be the general features for those
compounds. For further exploring the ferromagnetic quantum critical phenomena, we
studied CeSix, a Ce-based ferromagnet under pressure. CeSix (1.6<x<2) is believed to
be the first case of a ferromagnetic dense Kondo system[2], the curie temperature(TC)
can be various with different x. The strongly reduced effective moment of the system
is the result of Kondo screening in the lattice. A dc susceptibility study under pressure
show that when x~1.82, TC is decreasing under pressure and can be suppressed
continuously down to 2 K at about 13 kbar[3], and further measurements we have done,
including resistivity, ac heat capacity and ac susceptibility measurements under
pressure indicate that there might be a ferromagnetic quantum critical point in that
system.
Reference:
[1] A. Steppke et al., Science 339,933 (2013)
[2] Sato et al., JPSJ 57, 1384 (1988)
[3] S. Drotziger et al., PRB 73, 214413 (2006)
243
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Tu 13:30-15:30
Incommensurate magnetism near quantum criticality in the Kondo
lattice CeNiAsO
Shan Wu1, W.Adam Phelan1,2, L.Liu3, Neuefeind J.C.4, Feygenson M.4, M. B. Stone4, Gerald
Morris5 , Jennifer Morey1, David Tam6, Sarah Dunsiger7, Tyrel Mcqueen1 , Y. J. Uemura3 , and C.
Broholm1
1
Department of Physics and Astronomy and Institute for Quantum Matter, Johns Hopkins
University , Baltimore, Maryland 21218, USA
2
Department of Physics, Louisiana State University, Baton Rouge, Louisiana, USA
3
Department of Physics, Columbia University, New York, New York 10027, USA
4
Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
5
Canada's national laboratory for particle and nuclear physics, Vancouver, BC, Canada
6
Department of physics, Rice University, Houston, Texas, USA
7
Department of Physics, Ohio State University, Columbus, Ohio 43210, USA
CeNiAsO is isotructural to the 1111 Fe-based superconductors but exhibits Rareearth based heavy fermion magnetism near a pressure driven critical point at 6.5 kbar
[1]. At ambient pressure CeNiAsO has two phase transitions at TN1 ~ 9.3K and TN2 ~
7.3K that we have probed by neutron scattering and zero field muon spin relaxation
measurements. We find an incommensurate uniaxial spin density wave for T < TN1 .
TN2 is an incommensurate to commensurate transition where spins also re-orientate
within the ab plane to form a non-collinear spin structure. In inelastic neutron scattering
meausrements we find broad crystal field like excitations that evidence an easy-plane
spin system, consistent with the ordered structure.
Reference:
[1] Luo, Y. et al. Nature Material 13,777-781(2014)
244
Tu-P017
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Tu 13:30-15:30
Electronic structure and lattice dynamics of α, β, γ and δ-Ce
investigated by DFT+DMFT method
Haiyan Lu1, Li Huang2, Xi Dai*1
1Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese
2Institute of Materials, China Academy of Engineering Physics, P.O. Box 919-71, Mianyang,
China
The electronic structure and lattice dynamical properties of α, β, δ and γ phases of
cerium have been systematically investigated by using the charge self-consistent
combination of density-functional theory (DFT) and dynamical mean-field theory
(DMFT)[1]. The band structure, partial density of states, Fermi surface and atomic
multiplets of α, β, δ and γ-Ce have been comprehensively studied by employing the
DFT+DMFT method. The calculated band structure and partial density of states are
consistent with experimental results. The electronic structure shows the increasing
correlation of f electron from α to γ-Ce. Moreover, the lattice dynamics not only gives
the dynamical stability of α, β, δ and γ-Ce, but also provides the thermal dynamical
properties.
Reference:
[1] K. Hauleet al., Phys. Rev. B 81, 195107 (2010)
245
Tu-P018
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Tu 13:30-15:30
Delayed Kondo coherence with dilute carrier density in Cerium
based nickel pnictides
Peng Zhang1, Jianhui Dai2, K. Haule3
1
Department of Applied Physics, Xi'AnJiaotong University, Xi'An 710049, China
3
Department of Physics, Rutgers University, Piscataway, New Jersey 08854, USA
2
Recent experiment1 indicates a novel quantum phase transition in the Cerium based
nickel pnictides CeNi2−δAs2 (δ≈0.28). At increased external pressure, the
antiferromagnetic phase in the CeNi2−δAs2 is replaced by a disordered phase exhibiting
the delayed Kondo coherence. Using the density functional theory and dynamical
mean-field theory (DFT+DMFT)2, we calculated the respective electronic structures of
CeNi2As2 and CeNi2P2. We find a rather small contribution of Ni 3d orbitals to the
carrier density in the both cases and a significant Kondo resonance peak in the case of
CeNi2P2. We discuss how the Nozieres exhaustion scenario3 could be related to a
similar unconventional local-moment type of quantum phase transition driven by
chemical pressure via isovalence As/P substitution4, considering the dilute conduction
electron density in these CeNi2−δAs2/ CeNi2−δ P2 materials.
Reference:
[1] Yongkang Luo, et al. PNAS, 122, 13520 (2015).
[2] Kotliar, G. et al. Rev. Mod. Phys. 78, 865–951 (2006).
[3] Ph. Nozières, Eur. Phys. J. B 6, 447(1998).
[4] Jian Chen et al., unpublished, 2015.
246
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Exchange field effect in the crystal-field ground state of CeMAl4Si2
K. Chen1, F. Strigari1, M. Sundermann1, S. Agrestini2, E. D. Bauer3, J. L. Sarrao3, J.
D. Thompson3, E. Otero4, A. Tanaka5, and A. Severing1
1
Institute of Physics II, University of Cologne, Zülpicher Strasse 77, 50937 Cologne, Germany
2
Max Planck Institute for Chemical Physics of Solids, Nöthnizer Strasse 40, 01187 Dresden,
Germany
3
Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
4
Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, 91192 Gif-sur-Yvette, France
5
Department of Quantum Matter, AdSM, Hiroshima University, Higashi-Hiroshima 739-8530,
Japan
The crystal-field ground state wave functions of the tetragonal Kondo lattice
materials CeMAl4Si2 (M=Rh, Ir and Pt) are determined with low-temperature linearly
polarized soft x-ray absorption spectroscopy, and estimates for the crystal-field splitting
are given from the temperature evolution of the linear dichroism. Surprisingly, at T <
20 K, which is far below the first excited crystal-field level at T ~ 200K, a change in
linear dichroism, was observed that cannot be accounted for by population of crystalfield states. Adding an exchange field to the ionic full multiplet calculations below 20
K, leads to a splitting of the ground state doublet and a modification of the Jz admixture,
thus accounting for the change in the low-temperature linear dichroism. The direction
of the required exchange field is along c-axis for the antiferromagnetic Rh and Ir
compounds, and perpendicular to c-axis for the ferromagnetic CePtAl4Si2.
247
Tu-P020
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Tu 13:30-15:30
Substitution Effect of Zn-site in a Heavy Fermion Compound
YbCo2Zn20
R. Kobayashi1, H. Takamura2, Y. Higa2, H. Iwashita1, K. Kakazu1,2, T. Oooka1, K.
Matsubayashi3,4, Y. Uwatoko3, and N. Aso1
1Faculty of Science, University of the Ryukyus, Nishihara, Okinawa, Japan
2Graduate School of Engineering and Science, University of the Ryukyus, Nishihara, Okinawa,
Japan
3Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba, Japan
4Graduate School of Informatics and Engineering, the University of Electro-Communications,
Chofu, Tokyo, Japan
The heavy fermion compound YbCo2Zn20 (γ = 8 J/mol・K2) shows pressure-induced
antiferromagnetic transition at PC~1.5GPa which is relatively low value in Yb
compounds[1]. The existence of such huge γ and low PC indicates that this compound
is located near quantum critical point (QCP). Recently, we have succeeded in growing
single crystals of YbCo2(Zn1-xXx)20 (X = Cu, Ga, and Cd) systems and to detect the
slightly change of their lattice constant due to the substitution effect. In Ga and Cd
substituted systems, the magnetic component of electrical resistivity ρmag decreases
with increasing x, which implies that these systems go away from QCP. On the
otherhand, the increase of ρmag with increasing x is observed in Cu substituted
system,which suggests that this system may be close to QCP. This difference is
consistentwith their change of the lattice constant.
Reference:
[1] Y. Chen et al., PRL 114, 146403 (2015)
248
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Neutron Scattering Study in Single-Crystalline YbCo2Zn20
Naofumi Aso1, Yasuyuki Higa2, Riki Kobayashi1, Kazuyuki Matsubayashi3, Yoshiya
Uwatoko4, Hideki Yoshizawa4, Adam A. Aczel5, Tao Hong5
1Faculty of Science, University of the Ryukyus, Nishihara, Okinawa, Japan
2Graduate School of Engineering and Science, University of the Ryukyus, Okinawa, Japan
3Graduate School of Informatics and Engineering, University of Electro-Communications,
Chofu, Tokyo, Japan
4Institute for Solid State Physics, University of Tokyo, Kashiwa, Japan
5Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
Inelastic neutron scattering experiments on a heavy fermion Yb compound
YbCo2Zn20 were performed to investigate a nature of its magnetic excitations. We
succeeded in observing wavevector k-dependent magnetic excitations using a large
“single” crystal. Crystal-field excitation centered around 0.7 meV has k-dependent
intensities with little k-dependent excitation energies, implying none-existence of the
magnetic correlation characterized by the wave vector τ = (0 0 1), which corresponds
to the wave vector of the pressure-induced antiferromagnetic phase. No distinct 2.0
meV crystal-field excitation observed in this work. Quasi-elastic magnetic peaks has
also k-dependent intensities, which probably indicating that the moments fluctuate with
polarization along the a-axis.
249
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Tu 13:30-15:30
XANES study on Mg-doped valence transition compound YbInCu4
Tao Zhuang1, K. Matsumoto1, K. Hiraoka1, M. Kurisu1, K. Konishi1, T. Kamimori1, I. Nakai2
1
Graduate School of Sci. and Eng., Ehime University, Bunkyoucho-3, Matsuyama, Ehime 7908577, Japan
2Graduate School of Eng., TiFREC, Tottori University, koyamacyominami 4-101, Tottori city,
Tottori 680-8552, Japan
First-order valence phase transition compound YbInCu4 (Tv = 42 K) was found by
I. Feiner and I. Nowik [1]. We synthesized Mg-doped YbIn1-xMgxCu4 (0<x<1)
compounds by flux method in order to clarify the valence phase transition mechanism
and all of them were single crystal except YbMgCu4. The crystal structure of YbIn1xMgxCu4
(0<x<1) are confirmed C15b type one by XRD results. Yb-LIII XANES(X-
ray Absorption Near Edge Structure) measurements show that the Yb valence of YbIn1xMgxCu4 (0<x<0.9) decrease linearly from 2.87+0.02 to 2.78+0.02 with increasing x
at 295 K and have weak temperature dependence. The valence of Yb in YbMgCu4
shows 2.56+0.02 at 295K and 2.53+0.02 at 11K. It suggests that Mg-doping for
YbInCu4 causes valence fluctuating state of Yb ion.
Reference:
[1] I. Feiner and I. Nowik, Phys. Rev. B 33 (1986)
250
Tu-P023
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Tu 13:30-15:30
Different Valence States of Tm in YB6 and YbB6
H. Sato1, H. Nagata2, F. Iga3, Y. Osanai4, K. Mimura5, H. Anzai5, K. Ichiki5, S. Ueda6, T.
Takabatake7, A. Kondo8, K. Kindo8, K. Shimada1, H. Namatame1, M. Taniguchi1
1Hiroshima Synchrotron Radiation Center
2Graduate School of Science,
3College of Science,
4Graduate School of Science and Engineering, Ibaraki University, Mito, Ibaraki
5Graduate School of Engineering, Osaka Prefecture University, Sakai, Japan
6Synchrotron X-ray Station at SPring-8, National Institute for Materials Science, Hyogo,
Japan 7Graduate School of Advanced Sciences of Matter, Hiroshima University, HigashiHiroshima, Japan
8Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba
Rare-earth hexaborides RB6 exhibit a wide variety of physical properties depending
on R such as antiferroquadrupole order in CeB6 and valence fluctuation in SmB6.
Although TmB6 has not been synthesized so far, the lattice parameters of La1-xTmxB6
and Yb1-xTmxB6 suggested that TmB6 would be a valence fluctuation compound [1].
In this study, we have investigated the Tm valence states of Y1-xTmxB6 and Yb1xTmxB6 by means of hard x-ray photoemission spectroscopy (HAXPES) at hν = 5.95
keV carried out at BL15XU of SPring-8.
We found that the Tm valence state changes depending on the host material either
YB6 or YbB6. The Tm 3d HAXPES spectra of Y0.75Tm0.25B6 exhibit both Tm2+
and Tm3+ components clearly, which directly reveals the strong fluctuation of the Tm
valence. The Tm2+ (Tm3+) component increases (decreases) on cooling as often
observed in the Yb-based valence fluctuation compounds. The Tm valence deduced
from the spectra decreases from 2.68 at 300 K to 2.60 at 20 K. On the other hand, the
spectrum of Yb0.8Tm0.2B6 shows only Tm3+ components, indicating that Tm is
substituted for Yb in a trivalent state. From the Yb 3d spectra, the Yb valence remains
in a divalent state as in YbB6. The Yb2+ 4f7/2 peak just below the Fermi level is shifted
to the deeper binding-energy side, indicating that the Yb2+ state is stabilized by the Tm
substitution.
Reference:
[1] M. Kasayaet al., J. Magn. Magn.Mater.31, 389 (1983)
251
Tu-P024
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Tu 13:30-15:30
Photoemission study on Kondo lattices Yb2Pt6X15 (X=Al, Ga)
A.Rousuli1, H. Sato2, S. Nakamura3, Y. Matsumoto4, T. Ueda4, S. Ohara4, T.
Nagasaki1, K. Mimura5, H. Anzai5, K. Ichiki5, S. Ueda6, K. Shimada2, H.
Namatame2, M. Taniguchi2
1
2
3
4
Hiroshima Synchrotron Radiation Center,
Faculty of Science, Hiroshima University, Higashi-Hiroshima, Japan
Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, Japan
5
6
Graduate School of Science,
Graduate School of Engineering, Osaka Prefecture University, Sakai, Japan
Synchrotron X-ray Station at SPring-8, National Institute for Materials Science, Hyogo, Japan
Recently, we investigated electronic structure of the Kondo lattices YbNi3X9 (X=Al,
Ga) by means of hard x-ray photoemission spectroscopy [1]. YbNi3Al9 with an
antiferromagnetic ordering below 3.4 K and YbNi3Ga9 with no magnetic ordering with
the Kondo temperature of 570 K [2] occupy opposite sides in the Doniach phase
diagram across a quantum critical point. The Yb valence of YbNi3Al9 is close to be v~3,
while that of YbNi3Ga9strongly fluctuates with v~2.6. The Ni 2p and Yb3+ 4f peaks of
YbNi3Al9 are shifted to higher and lower binding-energy sides, respectively, compared
to YbNi3Ga9. In this study, we have investigated the electronic structure of Yb2Pt6X15
with analogous crystal structure to YbNi3X9, by means of photoemission spectroscopy
with hard x-ray and ultraviolet regions. The Somerfield coefficients are estimated to be
330 mJ/mole K2/Yb-ion for Yb2Pt6Al15 [3] and 13 mJ/mole K2/Yb-ion for Yb2Pt6Ga15
[4] and the X dependence is similar to YbNi3X9 with 100 (YbNi3Al9) and 30 (YbNi3Ga9)
mJ/mole K2 [2]. The experiments were done at BL15XU of SPring-8 and BL-7 of
Hiroshima Synchrotron Radiation Center.
The Yb 3d spectra of Yb2Pt6Al15 show both Yb2+ and Yb3+-derived structures,
indicating strong valence fluctuation. The Yb valence is estimated to be v~2.90 at 250
K and gradually decreases to v~2.83 with on cooling to 20 K. On the other hand, the
Yb 3d spectrum of Yb2Pt6Ga15 with v~2.43 at 300 K exhibits almost no temperature
dependence. The Pt 5d, Pt 4f and Pt 4d5/2 spectra of Yb2Pt6Al15 are shifted to higher
binding-energy side compared to Yb2Pt6Ga15, while the Yb3+ 4f spectra to opposite side.
These trends are just similar to those observed for YbNi3X9 [1]. The same results are
also obtained for antiferromagnetic YbNiSi3 and non-magnetic YbNiGe3 [5]. The Yb3+
4f energy shift indicates that the Yb hole level of Yb2Pt6Al15 is closer to the Fermi level
(EF) compared to Yb2Pt6Ga15 and the Yb valence of Yb2Pt6Ga15 gets closer to Yb2+.
The charge transfer from the conduction-band to Yb 4f states causes the energy shift of
EF in the conduction-band density of states, which is observed as the energy shifts of
the Pt core states.
Reference:
[1]
[2]
[3]
[4]
[5]
Y. Utsumiet al., Phys. Rev. B 86, 115114 (2012).
T. Yamashita et al., J. Phys. Soc. Jpn. 81, 034705 (2012).
M. Deppeet al., New J. Phys 10, 093017 (2008).
Y. Matsumoto et al., to be published in J. Phys. Conf. Series.
H. Sato et al., Phys. Stat. Solidi C 12, 620 (2015).
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Optical study of the mix-valence compound YbFe2Al10
J.L.Lv1, H. P. Wang1, R.Y.Chen,2 N. L. Wang2
1
2
Institute of Physics, Chinese Academy of Sciences, Beijing, China
We present an optical spectroscopy study on YbFe2Al10 single crystal which exhibits
a mixed-valent nature. The compound crystallized in a cagelike structure with space
group Cmcm was grown using an aluminum self-flux method. The measurements
reveal a gradual suppression of low frequency spectral weight below 900 cm-1 and a
formation of strong dip near 200 cm-1 in optical conductivity at low temperature.
Meanwhile a narrow Drude component develops at low frequency. The suppressed
spectral weight is transferred to the region between 900 cm-1 and 1800 cm-1, resulting
in a peak in the mid-infrared region. The observed features are common to heavy
fermion compounds. The relatively higher energy scale of the mid-infrared peak, being
associated with the effect of hybridization between f-electrons of Yb and conduction
electrons, is attributed to the stronger hybridization strength in the mixed-valent state.
253
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Magnetic order of YbMn2Sb2 single crystals studied by μSR
Julian Munevar1, Fernanda P. Vieira2, Raquel A. Ribeiro2, Elvezio Morenzoni1
1
Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, Villigen, Switzerland
2
Quantum Materials Group, Federal University of ABC, Santo André, Brazil
Intermetallic layered compounds have been subject of research due to their wide
range of physical properties, such as superconductivity, quantum criticality, heavy
fermion systems and in general strongly correlated systems. Here we present
preliminary magnetic studies on the YbMn2Sb2 single crystals grown by the flux
method. It has been observed from magnetization and heat capacity measurements a
magnetic transition at 570 K, followed by a second transition at 116 K. It is likely, from
these measurements, that the Mn moments are aligned along the c axis and suffer a spin
canting. However, from ZF muon spin rotation experiments, it is not observed any
precession above 130 K, whereas a asymmetry loss is observed at 5 K. All the possible
explanations of the data will be discussed.
254
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Probing the magnetic structure of EuPtIn4 via x-ray resonant
magneticscattering
J. R. L. Mardegan1, S. Francoual1, P.F.S. Rosa2,3, M. Saleta3, C.B.R. de Jesus3, J. Strempfer1, Z.
Fisk2, P.G. Pagliuso3, and E. Granado3
1
DeutschesElektronen-Synchrotron DESY, Hamburg - HH, Germany
3
Instituto de Física “GlebWataghin,” UniversidadeEstadual de Campinas, Campinas – SP, Brazil
2
High quality EuPtIn4 single crystals were investigated at low temperature
usingmagnetic X-ray resonant scattering. At the resonant energy of the Eu ions (7617
eV – L2 edge), magnetic incommensurate reflections of type (1/2, 1/2, τ) with τ = 0.427
were measured. A temperature dependence performed at the (1/2, 23/2, 0.427) peak
reveals an AFM coupling below TN = 13.13(4) K with a critical exponent of β = 0.42(3).
The temperature dependence does not show any magnetic anomaly related to a second
phase transition as suggested in previous macroscopic measurements [1-2]. Possible
evidence for the divalent state of the Eu ions, suggesting an intermediate valence state,
was not observed in our investigation in which the fluorescence measurements only
report one feature around the energy edge for the magnetic Eu2+ ions. In order to
determine the magnetic structure at low temperature, full polarization analysis method
[3] were carried out at selected magnetic reflections and at several temperatures. For
the wholetemperature range below TN, the measurements suggest that the Eu ions are
lying in the ac-plane with a cycloidal structure propagating along the c-axis. The
incommensurate and cycloidal phase can be addressed due to the RKKY interaction
between the first Eu neighbors in which the Eu ions present the same distance but with
different coupling parameters.
Reference:
[1] P.F.S. Rosa, et al., JMMM 371, 5-9 (2014).
[2] P. Kushwaha, et al., Cryst. Growth Des. 14, 2747 (2014).
[3] C. Detlefset al., Eur. Phys. J. Special Topics 208, 359 (2012).
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Pressure Evolution of Characteristic Electronic States in EuRh2Si2
F. Honda1, K. Okauchi1, A. Nakamura1, D.X. Li1, D. Aoki1, H. Akamine2, Y. Ashitomi2,
M. Hedo2, T. Nakama2, and Y. Onuki2
1
2
Institute for Materials Research, Tohoku University, Oarai, Ibaraki, 311-1313 Japan
Faculty of Science, University of the Ryukyus, Senbaru 1, Nishihara, Okinawa, 903-0213, Japan
Most of Eu compounds are in the divalent electronic state and order magnetically,
while some Eu compounds are in the trivalent electronic state. Eu-valence can be
changed against temperature, magnetic field, and pressure. Especially, a pressureinduced valence transition has been attracted much attention in the characteristic
electronic state. EuT2X2 (T: transition metal, X: Si, Ge) compounds exhibit the valence
transition at ambient and/or high pressures [1-3]. EuRh2Si2 is well known to reveal the
valence transition at about 1 GPa. The previous studies were carried out using
polycrystalline samples. We have succeeded in growing single crystals of several
EuRh2Si2 by the Bridgman method and studied electronic properties measuring the
electrical resistivity under pressure. EuRh2Si2 indicates a first–order valence transition
between 1 and 2 GPa with a large hysteresis in the temperature dependence of the
electrical resistivity. At higher pressures, the first– order valence transition is changed
into the second-order one and the temperature dependence of the electrical resistivity
shows a typical behavior for a intermediate valence state. Finally, at 5 GPa, the
resistivity reveals a normal metallic behavior in the nearly trivalent electronic state.
This is the first report on pressure evolution of the electronic states from the
antiferromagnetically ordered state to the intermediate valence state via the first-order
valence transition. We also present the similar experimental results of EuNi2Ge2 and
EuIr2Si2.
Reference:
[1] B. K. Cho et al.: J. Phys. Soc. Jpn. 71, Suppl. 252 (2002)
[2] H. J. Hesse et al.: J. Alloys Compd. 246, 220 (1997)
[3] A. Mitsuda et al.: J. Phys. Soc. Jpn. 81, 023709 (2012)
256
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Temperature-Dependent Electronic Structure of EuNi2P2
Revealed by Angle-Resolved Photoemission Spectroscopy
H. Anzai1, K. Ichiki1, Eike F. Schwier2, H. Iwasawa2, K. Shimada2, H. Namatame2, M.
Taniguchi2, A. Mitsuda3, H. Wada3, and K. Mimura1,2
1
2
Graduate School of Engineering, Osaka Prefecture University, Sakai, Japan
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Japan
3
Graduate School of Science, Kyushu University, Fukuoka, Japan
Mixed-valent EuNi2P2 shows a large electronic specific heat coefficient γ ~ 100
mJ/(K2·mol) and is known as a heavy-fermion compound [1]. In this system, the
temperature variation of 4f-electron contribution to the volume thermal expansion
scales well with that of the Eu mean valence [2]. This implies that the charge transfer
of Eu 4f electrons is relevant to the heavy-fermion behavior. Hence, the temperature
dependence of electronic structure may provide important insights into the mechanism
of the heavy-fermion state in EuNi2P2.
In our work, a sudden increase of the spectral intensity for Ni 3d states below 180 K
was found from angle-resolved photoemission spectroscopy measurements. This
upturn of the intensity is considered that the Eu 4f electrons transfer to the Ni 3d states
and is consistent with the shrinkage of the 4f-electron contribution to the volume
thermal expansion at low temperature. Our results suggest that the hybridization effect
plays an essential role for the heavy-fermion state in EuNi2P2.
Reference:
[1] R. A. Fisher et al., Phys. Rev. B 52, 13519 (1995).
[2] Y. Hiranakaet al., J. Phys. Soc. Jpn. 82, 083708 (2013).
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Magnetic Transitions in the Chiral Armchair-Kagome System
Mn2Sb2O7
Darren C. Peets,1, 2 Hasung Sim,1, 2 Seongil Choi,1, 2 Maxim Avdeev,3 Seongsu Lee,4 Su Jae Kim,4
Hoju Kang,5 Docheon Ahn,5 and Je-Geun Park1, 2
1
Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 151-747, Korea
2
3
Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia
4
Neutron Science Division, Korea Atomic Energy Research Institute, Daejeon 305-353, Korea
5
Beamline Department, Pohang Accelerator Laboratory, 80 Jigokro-127-beongil, Nam-gu,
Pohang 790-784, Gyeongbuk, Korea
Mn2Sb2O7 [1–3] forms in a chiral kagome-based structure, similar to that of the
trigonal Weberites, in which a fourth member is added to the kagome-plane triangles
to form an armchair unit and link adjacent kagome planes. This structural motif may be
viewed as intermediate between the triangles of the kagome network and the tetrahedra
encountered in a pyrochlore lattice. Previous reports on Mn2Sb2O7 have indicated bulk
magnetic order below 13 K, with history dependence evident in the magnetization to
much higher temperatures [4]. We show that the material actually exhibits two distinct
magnetic phase transitions, at 11.1 and 14.2 K, at least one of which has a weak ferromagnetic component. This is preceded by an onset of short-range spin correlations
around 50 K, but without history dependence. The propagation vector describing the
magnetic Bragg peaks does not appear to change through the lower transition,
suggesting a metamagnetic transition or a transition involving a multi-component order
parameter. Although previously reported in the P 3121 space group, the material
actually crystallizes in the P 2 space group, which allows ferroelectricity, and we show
clear evidence of magnetoelectric coupling suggestive of multiferroic order.
Reference:
[1] H. G. Scott, J. Solid State Chem. 66, 171 (1987).
[2] H. G. Scott, Z. Kristallogr. 190, 41 (1990).
[3] L. Chelazzi, T. B. Ballaran, G. O. Lepore, L. Bindi, and P. Bonazzi, Solid State
Sci. 21, 85 (2013).
[4] J. N. Reimers, J. E. Greedan, C. V. Stager, M. Bjorgvinnsen, and M. A.
Subramanian, Phys. Rev. B 43, 5692 (1991).
258
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Resonating-Valence-Bond physics is not always governed by the
shortest tunneling loops
Arnaud Ralko1 and Ioannis Rousochatzakis2
1
2
Institut Néel, University Grenoble Alpes & CNRS, Grenoble, France
School of Physics and Astronomy, University of Minnesota, Minneapolis, USA
It is well known that the low-energy sector of quantum spin liquids and other
magnetically disordered systems is governed by short-ranged resonating-valence bonds.
Here [1], we show that the standard minimal truncation to the nearest-neighbor valencebond basis fails completely even for systems where it should work the most, according
to received wisdom. This paradigm shift is demonstrated for the quantum spin-1/2
shuriken (square-kagome), where the strong geometric frustration, similar to the
kagome, prevents magnetic ordering down to zero temperature. The shortest tunneling
events bear the strongest longer-range singlet fluctuations, leading to amplitudes that
do not drop exponentially with the length of the loop L, and to an unexpected loop-six
valence-bond crystal, which is otherwise very high in energy at the minimal truncation
level. The low-energy effective description gives in addition a clear example of
correlated loop processes that depend not only on the type of the loop but also on its
lattice embedding, a direct manifestation of the long-range nature of the virtual singlets.
Reference:
[1] A. Ralko & I. Rousochatzakis, PRL 115, 167202 (2015)
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Uniaxial-pressure effect on the magnetic frustration in the Ybbased triangular lattice antiferromagnet YbCuGe
K. Umeo1, D. Watanabe2, K. Araki3, K. Katoh3, T. Takabatake4
1
N-BARD,2AdSM, 4IAMR, Hiroshima Univ., Higashi-Hiroshima, Japan 3Dept. Appl. Phys. NDA,
Yokosuka, Japan
We report the uniaxial and hydrostatic pressure effects on the antiferromagnetic
order of YbCuGe with a triangular lattice of Yb ions in the c plane of the hexagonal
LiGaGe-type structure. The antiferromagnetic order takes place at TN=4.2 K, in which
the magnetic frustration effect manifests itself in a pronounced tail of the specific heat
in the temperature range up to 2TN [1]. Under hydrostatic pressure up to 1.34 GPa and
uniaxial pressure P//c up to 0.15 GPa, where the Yb triangular lattice is hold, the TN
hardly changes. On the contrary, for P//a up to 0.17 GPa, where the Yb triangular lattice
is distorted, the TN increases up to 4.5 K. These contrasting responses indicate that the
distortion under P//a releases the magnetic frustration and stabilizes the
antiferromagnetic order in YbCuGe.
Reference:
[1] K. Katoh et al., J. Alloys Compd. 520, 122 (2012).
260
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Novel geometrically frustrated magnetic effects in Gd3Ru4Al12 and
Dy3Ru4Al12
Venkatesh Chandragiri1, Kartik K Iyer1 and E.V. Sampathkumaran1
1
Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
The rare-earth (R) family of the type R3Ru4Al12 is an interesting one among
intermetallics, as the structure contains layers, triangular lattice and Kagome lattice [1]
favoring magnetic frustration. The reports on the magnetic behavior of the members of
this rare-earth family is sporadic over a period of nearly two decades. Even the
prototype Gd member was not subjected to any magnetic investigation. Dy member
was reported to order antiferromagnetically below (TN=) 7 K [2]. We carried out ac and
dc magnetic susceptibility (χ) studies as well as isothermal magnetization (M) on these
two compounds. We show for the first time that the Gd member undergoes long range
antiferromagnetic ordering below 18.5 K far below its paramagnetic Curie temperature
(θp=+80 K), thereby indicating geometrically frustrated magnetism; antiferromagnetic
ordering prevails, despite exchange interaction between Gd ions, as indicated by the
sign of θp, is ferromagnetic (similar to that known for Dy compound (θp= +20 K)). A
new finding being reported (for Dy compound as well) is that there is an evidence for
another magnetic feature near 55 and 18 K for Gd and Dy compounds respectively,
which behaves like Griffiths phase. This finding suggests that the magnetic frustration
fights against an intermediate phase containing ferromagnetic clusters with lowering
temperature, before settling for long range antiferromagnetic order in these materials.
Finally, we find a distinct difference in the behavior of antiferromagnetic phases of Gd
and Dy members. That is, in the former, there is no evidence for any spin-glass features,
whereas, in the latter, some signatures of spin-glass below 7 K (frequency dependence
of ac χ, slow decay of isothermal remnant magnetization, and bifurcation of zero-fieldcooled and zero-field-cooled low-field dc χ) could be found. The results overall reveal
that it would be fruitful to subject this family of Kagome layered materials for further
studies to explore manifestations of geometrical frustration.
References:
[1]J. Niermann and W. Jeitschko, Z. Z. Anorg. Allg. Chem. 628, 2549 (2002).
[2]D.I. Gorbunov et al, Phys. Rev. B 90, 094405 (2014).
261
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Ultrasonic Study on the Hexagonal Antiferromagnet Dy3Ru4Al12
I. Ishii1, K. Takezawa1, H. Goto1, S. Kamikawa1, A. V. Andreev2, D. I. Gorbunov3, M. S.
Henriques2, T. Suzuki1,4,5
1
Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima, Japan
2
Institute of Physics, Academy of Sciences, Prague, Czech Republic
3
Dresden High Magnetic Field Laboratory, Helmholtz-Zentrum Dresden-Rossendorf, Dresden,
Germany
4
Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima, Japan
5
Cryogenics and Instrumental Analysis Division, N-BARD, Hiroshima University, HigashiHiroshima, Japan
The distorted kagome lattice antiferromagnet Dy3Ru4Al12 has the hexagonal
Gd3Ru4Al12-type structure (space group P63/mmc) with TN = 7 K [1]. The magnetic
susceptibility follows the Curie-Weiss law above 100 K and the effective magnetic
moments estimated are close to the value of the free Dy3+ ion. Dy3Ru4Al12 possesses
an almost localized character of 4f-electrons at high temperatures and the crystal
electric field (CEF) effect. To investigate the phase transition at TN and the CEF effect,
we performed ultrasonic measurements on a single-crystalline Dy3Ru4Al12 sample. At
high temperatures, both the longitudinal elastic modulus C11 and the transverse
modulus C44 increase monotonically with decreasing the temperature. Below 60 K a
characteristic elastic softening is observed in C44 in contrast to C11 without the softening.
We carried out the Curie-Weiss-type fitting for the softening and obtained a negative
parameter: Θ which is proportional to a quadrupole-quadrupole coupling constant
under the hexagonal CEF. With further decreasing the temperature, both moduli exhibit
abrupt elastic hardening at TN.
Reference:
[1] D. I. Gorbunov et al., PRB 90, 094405 (2014).
262
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Elastic softening in the metallic antiferromagnet YbCuGe
Xiaojuan Xi1, Isao Ishii1, Yoshihito Noguchi1, Hiroki Goto1, Shuhei Kamikawa1, Koji Araki2
Kenichi Katoh2, and Takashi Suzuki1,3,4
1
Department of Quantum Matter, ADSM, Hiroshima University, Higashihiroshima, Japan
2
Department of Applied Physics, National Defense Academy, Yokosuka, Japan
3
Institute for Advanced Materials Research, Hiroshima University, Higashihiroshima, Japan
4
Cryogenics and Instrumental Analysis Division, N-BARD, Hiroshima University, Higashihi roshima, Japan
The Yb-based compound YbCuGe with a hexagonal structure is reported as a
metallic antiferromagnet with TN= 4.2 K. It is also proposed that this compound
contains geometrical magnetic frustration due to the competition of exchange
interaction within the quasi-two dimensional Yb plane, which forms the triangle of Yb
ions. Recent research suggested that its magnetic anisotropy can be ascribed to the
crystalline electric field (CEF) effect on a single Yb ion. In order to investigate the
magnetic phase transition and the CEF effect in YbCuGe, ultrasonic measurements and
related theoretical calculation have been performed. The transverse elastic modulus C44
exhibits a large softening which begins at 120 K and stops at about 30 K. On the other
hand, in the temperature range higher than TN, the longitudinal modulus C33 mode
shows a continuous hardening. We carried out the theoretical strain-susceptibility
fitting of the transverse elastic modulus. The CEF parameters obtained by Katoh et al.
[1]
were used for the calculation. The fitting results indicate that the softening at high
temperature range can be explained by the quadrupole interaction between the ground
and excited Kramers doublets under the hexagonal CEF. Both the elastic moduli C33
and C44 show elastic softening below TN, suggesting a strong coupling between a strain
and a magnetic order parameter.
Reference:
[1] K. Katoh et al., J. Alloys Compd. 520, 122 (2012)
263
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Collinear and non-collinear magnetic order on the Cairo lattice
A.Tsirlin1, D. Batuk2, A. M. Abakumov2,3
1
2
Experimental Physics VI, EKM, University of Augsburg, 86159 Augsburg, Germany
EMAT Center for Electron Microscopy, University of Antwerp, 2020 Antwerp, Belgium
3
Skolkovo Institute of Science and Technology, 143026 Moscow, Russia
Pentagonal Cairo lattice is one of the less-known frustrated geometries, where
frustration is generated by antiferromagnetic interactions on closed loops with an odd
number of magnetic sites. Real-world manifestations of the Cairo-lattice magnetism
remain scarce. The best Cairo material available so far is Bi2Fe4O9, where orthogonal
magnetic order has been observed below TN ~ 242 K, in agreement with theoretical
predictions for the Cairo lattice.
In this talk, we will present a new Cairo-lattice frustrated antiferromagnet
Bi4Fe5O13F [1] investigated by thermodynamic measurements, neutron diffraction,
Mössbauer spectroscopy, and band-structure calculations. This compound shows Cairo
-like geometry of spin -5/2 Fe3+ ions in the plane as well as additional, weakly coupled
Fe3+ ions between the planes. It reveals three magnetic transitions at T1 = 62 K, T2 =
71 K, and TN = 180 K.
The magnetic state below T1 is orthogonal, akin to Bi2Fe4O9 and in agreement with
exchange couplings derived from density-functional calculations. The transitions at T1
and T2 are accompanied by a large release of entropy. Upon approaching T1 from below,
magnetic moments on the in -plane Fe sites re-orient toward a collinear configuration
that is observed between T1 and T2. Above T2, the in-plane moments re-orient again
toward another orthogonal configuration that is similar but not equivalent to the one
below T1.
These observations are intriguing in the light of theoretical predictions for the
quantum spin model on the Cairo lattice [2], where collinear phase stabilized by
quantum fluctuations is expected. This phase is, however, quantum in nature and thus
hard to reconcile with the largely classical spin-5/2 nature of Bi4Fe5O13 F. We will
discuss whether quantum or thermal fluctuations are responsible for the stabilization
of the collinear phase in this material, and which anisotropy effects can be relevant.
Reference:
[1] A. M. Abakumov et al. Phys. Rev. B 87, 024423 (2013).
[2] I. Rousochatzakis et al. Phys. Rev. B 85, 104415 (2015).
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NMR study on two dimensional spin-1/2 triangular-lattice
antiferromagnet YbMgGaO4
Ping Zhou1, Y. Li1, P. S. Wang1, W. Song1, T. R. Li1, Q. M. Zhang1, W. Yu1
1
Department of Physics, Renmin University of China, Beijing 100872
YbMgGaO4 is a two dimensional spin-1/2 triangular antiferromagnet with
anisotropic exchange interactions (~4 K) in the spin space, where site-mixing magnetic
defects and DM interactions are absent. This material offers a candidate spin liquid
state at low temperatures.
Here we report our 71Ga NMR study of the low-temperature magnetism on
YbMgGaO4 single crystals. We find no magnetic ordering from the NMR spectra and
the spin-lattice relaxation rate, with field from 0.48 Tesla to 6 Tesla and with
temperature down to 35 mK. In fact, both the Knight shift and the spin-lattice relaxation
rate saturate at constant values at the zero temperature limit, suggesting a gapless
ground state with strong spin fluctuations. Therefore, our data gives a strong support
for a gapless spin liquid state in YbMgGaO4.
265
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Magnetic Phase Diagram in Hyperkagome Iridate Na4Ir3O8
Tomonari Mizoguchi1, Yong Baek Kim2,3,
1
2
Department of Physics, University of Tokyo, Tokyo, Japan
Department of Physics and Center for Quantum Materials, University of Toronto, Toronto,
Canada
3
School of Physics, Korea Institute for Advanced Study, Seoul, Korea
Hyperkagome iridate Na 4Ir3O8[1] has attracted a great attention as a
candidate for a spin liquid state. In this material, Ir 4+ ions possess the
psudospin jeff=1/2, and they are on a hyperkagome lattice (i.e., the cornersharing triangles in three-dimensions), which is geometrically frustrated. So
far, it has been shown that anisotropic spin exchange interactions play an
important role in determining the classical ground state of this material[2-4].
In this presentation, we first derive a generic local-moment model, namely
the J-K-Gamma-D model, by taking into account multiorbital interactions and
the spin-orbit coupling for t2g orbitals. Then we discuss the magnetic phase
diagram of this model obtained by the Luttinger-Tisza approximation and the
simulated annealing (Fig. 1). We find that there are three major q=0 states: Z2,
Z62p, and Z61p states. We also discuss how the spin configurations of three
q=0 states can be understood in terms of the underlying lattice symmetries.
FIG. 1 Magnetic phase diagram in J-K-Gamma-D model with (a) D>0 and (b) D<0.
Reference:
[1] Y. Okamoto, et. al., Phys. Rev. Lett. 99, 137207 (2007).
[2] G. Chen, et. al., Phys. Rev. B 78, 094403 (2008).
[3] I. Kimchi, et. al., Phys. Rev. B 89, 014414 (2014).
[4]R. Shindou, arXiv: 1509.01002 (2015).
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Evolution of a magnetic order in the quasi-kagome lattice system
CeRh1-xPdxSn
C. L. Yang1, K. Umeo2, T. Takabatake1,3
1ADSM, 2N-BARD, 3IAMR, Hiroshima University, Higashi-Hiroshima, Japan
The equiatomic compound CeRhSn with a quasi-kagome lattice of Ce atoms displays
a non-Fermi liquid behaviors at low temperatures [1-3]. Recently, it has been reported
that the alloys CeRh1-xPdxSn retain the hexagonal structure up to x = 0.8 keeping the
ground state in a valence fluctuation state down to 2.5 K [4]. We have studied how the
ground state changes with x in this alloy system by measuring the specific heat C,
magnetic susceptibility , and resistivity  for polycrystalline samples of CeRh1-xPdxSn
(0 ≤ x  0.8). With increasing x, the hexagonal lattice parameters a and c increase almost
linearly, and the absolute value of paramagnetic Curie decreases, as was reported [4].
The resistivity for x = 0.2 and 0.5 turns up on cooling below 30 K, whereas that for x =
0.8 shows a metallic behavior with a sharp decrease at T = 3 K. At this temperature,
both  and C exhibit peaks, indicating the evolution of a long-range antiferromagnetic
order. Much sharper peaks in C were observed at 1.5 K and 1.0 K for x = 0.7 and x =
0.5, respectively. Our results indicate that the doping of 4d electrons in CeRhSn
destroys the coherence of the quasi-kagome lattice and weakens the hybridization
between the 4f state and conduction bands, leading to the evolution of antiferromagnetic
order in the vicinity of x  0.3.
Reference:
[1] A. Slebarski et al., Phil. Mag. B 82, 943 (2002).
[2] M. S. Kim et al., Phys. Rev. B 68, 054416 (2003).
[3] Y. Tokiwa et al., Sci. Adv. 1:e1500001 (2015).
[4] O. Niehaus et al., Z. Naturforsch. 70 b, 253 (2015).
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Anisotropic magnetic and transport properties of CePd1-xNixAl
Hengcan Zhao1, Jiahao Zhang1, Yosikazu Isikawa2, Frank Steglich3, Peijie Sun1
1
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese
2
Graduate School of Science and Engineering, University of Toyama, Toyama 930-8555, Japan
3
Max Plank Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
CePdAl is known as an antiferromagnetic (TN = 2.7 K) heavy-fermion compound
with geometrically frustrated Ce moments on a distorted Kagome lattice. Neutron
diffraction investigation has revealed that only two-third of the Ce moments are
magnetically ordered, with an incommensurate propagation vector. Previous
investigations on polycrystalline samples have indicated a quantum critical point
emerging when 14% Pd is substituted by Ni. These make CePdAl a good system for
studying interplay between quantum criticality and magnetic frustration. In this work
we have grown single crystals of CePd1-xNixAl with x =0, 0.1, 0.2 and 0.4 by
Czochralski method. Magnetic and electrical resistivity measurements reveal a striking
anisotropy in all the compounds. Multiple metamagnetic transitions were observed in
both low-temperature magnetization and magnetoresistance measurements. We will
discuss the impact of magnetic frustration on these features.
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Single crystal growth and magnetic properties of new pseudokagome lattice RRhPb (R = Nd, Sm, Gd)
Y. Matsumoto1, R. Goto1, S. Ohara1, Y. Haga2 and Z. Fisk2,3
1
Department of Engineering Physics, Electronics and Mechanics, Nagoya Institute of Technology,
Nagoya, Aichi, Japan
2
Advanced Science Research Center, Japan Atomic EnergyAgency,Tokai,Ibaraki, Japan
3
The hexagonal ZrNiAl-type structure with pseudo-kagome lattice is one of the
intensively studied system in the highly correlated f electron system. We have firstly
synthesized the RRhPb (R = Nd, Sm, Gd). The crystal structure was confirmed by
powder and single crystal X-ray diffraction method and the composition was
determined by EPMA. We have measured the resistivity, magnetic properties and heat
capacity of RRhPb (R = Nd, Sm, Gd). It is found that the RRhPb (R = Nd, Sm, Gd) are
antiferromagnet with two magnetic phase transitions.
269
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Interplay between charge and spin degrees of freedom induced by
charge frustration of electrons on a kagome lattice
K. Ferhatg1, A.Ralkog1
1
UniversitéGrenoble Alpes et CNRS, Grenoble, FR-38042 France
2
Los Alamos National
Geometrical frustration is at the center of intense theoretical and experimental
research activity of nowadays condensed matter, thanks to the extremely rich and exotic
quantum magnetic phases unravelled these last years. Together with the correlations,
the frustration also affects the charge degrees of freedom, and by competing with the
spins, makes room for unconventional physics. This is particularly true on the Kagome
lattice, the most frustrated two-dimensional lattice.
At 1/3 filling and under correlations, electrons on such a geometry obey local "icerule" constraints that make the classical ground state to be massively degenerated. We
show that the interplay between the charges and the spins, together with the frustration
allow for unconventional physics. In particular, we establish the presence of two
peculiar states of matter driven by the strong quantum fluctuations. The first one
consists of polarized droplets of metal standing on the hexagons of the lattice, and an
enlarged kagome pinned charge order, inversely polarized, on the remaining sites. The
second, obeying a local ice-rule type constraint on the triangles of the kagome site, is
driven by an antiferromagnetically coupling of spins and is constituted of disconnected
6-spin rings.Those phases perfectly illustrate the importance of the frustration on
charge ordered systems, as well as the strong resulting interplay with the spins.
The thermodynamic limit spectral properties of the two reported intriguing phases
are investigated. We obtain a very accurate description of the kinetic effects, expected
to play a crucial role in such parameter regimes. We discuss the main features and
photoemission characteristics that one would expect in ARPES experiments.
Reference:
[1] K.Ferhat and A. Ralko, Phys. Rev. B 89, 155141 (2014)
[2] K.Ferhat and A. Ralko, work in preparation (2016)
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Geometric Spin Frustration in Zn1-xNixCr2O4 System
H. Suzuki, H. Kaneko, A. Khan and S. Naher
Department of Physics, Kanazawa University, Kanazawa, Japan
Geometric frustration is one of the most interesting topics in the study of condensed
matter systems. Frustrated interactions often cause extensive degeneracy in the ground
state of the system and prevent any ordering down to low temperatures. The ground
state of a frustrated system is quite intriguing and can be modified into a novel and
interesting state, such as a spin liquid, associated with quantum fluctuations. The
degenerated states, however, remove its degeneracy in general by a broken symmetry,
such as a crystal distortion at low temperatures. A spinel compound ZnCr2O4 is known
to be the most typical material which shows the geometric frustration. At room
temperature, it has a cubic Fd3 m crystal structure where Cr3+ (S = 3/2) ions form a
network of corner-sharing tetrahedral. The Curie-Weiss temperature is -390 K
indicating strong antiferromagnetic frustration, yet Cr spins remain in a cooperative
paramagnetic phase down to TC = 12.8 K. There, a first order phase transition from a
cubic paramagnet to a tetragonal antiferromagnet signals the end of distinct spin and
lattice degree of freedom. In this distorted structure and magnetic ordered phase, the
resonating mode due to the frustrated fluctuation spread over the large scale molecule,
such as hexamer and heptomer, defined as antiferromagnetic spin correlations confined
in the molecule units was observed by the inelastic neutron scattering experiments. On
the other hand NiCr2O4 compound distorts from cubic to tetragonal structure at 310 K,
due to the Jahn-Teller Ni2+ ion. Though the geometric frustration should be suppressed
due to the distorted structure, the geometric frustration gives some effect on the
magnetic properties. The frustration index, θCW/TC = 7.2. The magnetic spin structure
and the crystal structures show the interesting phase transitions.
In the lowest phase of NiCr2O4 the
resonated mode due to the frustrated
fluctuation can bealso observed by the
neutron inelastic scattering experiments.
Due to the competition between the
geometric frustration interaction and the
Jahn-Teller interaction Zn1-xNixCr2O4
system can be expected to show the
interesting features. We investigated by the
SQUID and the low temperature x-ray
diffraction. In the figure the frustration
index vs. Ni concentration x is shown
271
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Magnetic-Field Effect on the Phase Transition of Classical
Heisenberg Model
Miso Yun and Gun Sang Jeon*
Department of Physics, Ewha Womans University, Seoul, Republic of Korea
Two-dimensional triangular-lattice Heisenberg model with nearest-neighbor
antiferromagnetic interaction is considered. Extensive Monte Carlo calculation is
performed to examine the effects of the single-ion anisotropy of an easy-plane type.
Particular attention is payed to the critical behavior on the boundaries of a variety of
phases. We also reveal the change in phase boundaries by the anisotropy strength.
272
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Signatures of indirect K-edge resonant inelastic x-ray scattering on
magnetic excitations in triangular lattice antiferromagnet
Dao-Xin Yao1, Cheng Luo1, Trinanjan Datta2
1
School of Physics, Sun Yat-Sen University, Guangzhou, China
2
Augusta University, Georgia, USA
We compute the K-edge indirect resonant inelastic x-ray scattering (RIXS) spectrum
of a triangular lattice antiferromagnet in its ordered coplanar 3-sublattice 120 degree
magnetic state. By considering the first order self-energy corrections to the spin wave
spectrum, magnon decay rate, bimagnon interactions within the ladder approximation
Bethe-Salpeter scheme, and the effect of three-magnon contributions up to 1/S- order
we find that the RIXS spectra is non-trivially affected. For a purely isotropic triangular
lattice model, the peak splitting mechanism and the appearance of a multipeak RIXS
structure is primarily dictated by the damping of magnon modes. At a scattering
wavevector corresponding to the zone center Γpoint and at the roton point q=M, where
the magnon decay rate is zero, a stable single peak forms. At the Γpoint, the contribution
is purely trimagnon at the 1/S level and occurs approximately at the trimagnon energy
of 6JS. The roton peak occurs at a lower energy of 4JS. The K-edge single peak RIXS
spectra at the roton momentum can be utilized as an experimental signature to detect
the presence of roton excitations. A unique feature of the triangular lattice K-edge RIXS
spectra is the nonvanishing RIXS intensity at both the zone centerΓpoint and the
antiferromagnetic wavevector K point. This result is in sharp contrast to the vanishing
K-edge RIXS intensity of the collinear magnetic phases on the square lattice. We find
that including XXZ anisotropy leads to additional peak splitting, including at the roton
scattering wavevector where the single peak destabilizes towards a two-peak structure.
The observed splitting is consistent with our earlier theoretical prediction of the effects
of spatial anisotropy on the RIXS spectra of a frustrated quantum magnet on square
lattice.
Reference:
[1] Cheng Luo, Trinanjan Datta, Zengye Huang, Dao-Xin Yao, Phys. Rev. B 92,
035109 (2015).
[2] Cheng Luo, Trinanjan Datta, Dao-Xin Yao, Phys. Rev. B 89, 165103 (2014)].
[3] Cheng Luo, Trinanjan Datta, Dao-Xin Yao, to be submitted.
273
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Evolution of Structural and Magnetic Properties in Hole Doped
Sr2IrO4
Imtiaz Noor Bhatti1* and A. K. Pramaink1
1
School of Physical Sciences, Jawaharlal Nehru University,
New Delhi,India. *[email protected]
Recently 5d transition metal oxides (TMOs) specially iridates and osmates have
received extensive attention of researchers due to potential for exotic physics driven by
competing interactions viz. crystal field effect (CFE), spin-orbital interaction (SOI) and
onsite Coulomb interaction (U). Moreover, crystallographic structure of material also
plays vital role. Over the past several years the most comprehensively studied iridate is
Sr2IrO4; being isostructure and iso electronic to high TC cupric superconductor
La2CuO4. The Sr2IrO4 draw interest as it has been theoretically predicted to be
superconductor electrons/hole doping. The layered perovskite Sr2IrO4 believed to
stabilize in Jeff = ½ ground state and it is a magnetic insulator. The Sr2IrO4 belongs to
K2NiF4 family of compound and crystallize in reduced tetragonal structure with space
group I41/acd. The reduced symmetry is due to rotation of IrO6 octahedral around caxis and play key role in physical properties of Sr2IrO4. The magnetic ground state in
Sr2IrO4 is believed to be canted type antiferromagnetic (AFM) which gives
ferromagnet component with magnetic ordering around 240 K to this material. The spin
canting is rendered by Dzyaloshinskii-Moriyam anti-symmetric interaction driven by
SOI and rotated IrO6 octahedra. We endeavor to tune SOI and U in Sr2IrO4 by
substituting Ru4+ (4d4 S = 1) for Ir4+ (5d5 Jeff = 1/2). Since Ru4+ has four electrons in
4d orbital hence not only reduces the SOI but also introduce a hole in t2g band. We
have studied the effect of Ru doping on structural and magnetic properties. We observe
compression in unit cell thereby decreasing both a and c lattice parameters in the
meantime Ir-O-Ir bond angle also increases justify decrease in octahedral rotation
(θOct). Further, our magnetization study shows suppress in transition (TC) reduction in
coercivity and remanence with Ru doping. Thus we observe introduction of hole in
Sr2IrO4 prominently effect the structural and magnetic properties.
References:
[1]B. J. Kim et al., Phys. Rev. Lett. 101 076402 (2008)
[2]Moon S. J. et al., Phys. Rev. Lett. 101 226402 (2008)
[3]Yang Y et al., Phys. Rev. B 89 094518 (2014)
[4]Bhatti et al., J. Phys.: Condens. Matter 27, 016005 (2014)
[5]Crawford M. K. et al., Phys. Rev. B 49 9198 (1994)
[6]Bhatti et al., arXiv:1512.02041 (2015)
274
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Nuclear magnetic resonance and nuclear quadrupole resonance
study on superconducting Sr2 RuO4
Masahiro Manago1, Takayoshi Yamanaka1, Kenji Ishida1, Zhiqiang Mao1, Yoshiteru Maeno1
1
Department of Physics, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan
A layered ruthenate Sr2 RuO4 exhibits unconventional superconductivity and is a
candidate of spin-triplet, equal-spin pairing. However, some unresolved issues remain
in the SC state of Sr2 RuO4 . One is anomalous behavior of nuclear spin-lattice
relaxation rate 1/T1 measured by in-plane 17O-nuclear quadrupole resonance (NQR) in
the SC Sr2RuO4 in zero magnetic field. This suggests the presence of low-energy
magnetic fluctuations along the c axis [1]. Although this result might be crucial for
determining the intrinsic SC state under zero field, there have been no other reports
suggesting such anomalous magnetic fluctuations. Therefore additional experiments
are desired for clarifying the physical origin of the magnetic fluctuations in the SC state.
Another issue is suppression of the upper critical field H𝐶2 in the field parallel to the
RuO2 plane. According to the NMR Knight-shift results, H𝐶2 in this field direction is
expected to be determined only by the orbital effect due to the absence of the Pauliparamagnetic effect. However, the in-plane H𝐶2 of Sr2 RuO4 is strongly limited, and
the SC-normal transition is of first-order below 0.8 K [2] accompanied by a sharp
magnetization jump at low temperatures [3]. The orbital limit leads to the second-order
transition, and thus it seems that this first-order transition (FOT) cannot be explained
in the present spin-triplet scenario.
We carried out measurements of 101Ru-NQR in zero field and 17O-NMR under inplane high fields on a single-crystal Sr2 RuO4 to clarify the above unresolved issues.
We found that nuclear spin-spin relaxation rate 1/T2 measured by 101Ru-NQR is
enhanced in the SC state. The origin of the enhancement is considered as identical one
in the previous 17O-NQR result. Enhancement of 1/T2 in the SC state is quite unusual
since 1/T2 decreases in the SC state in most superconductors due to the spin-singlet
pairing. We suggest that the enhancement of 1/T2 is further evidence of the presence of
spin degrees of freedom in the SC state of Sr2 RuO4 . We also found that the 17O-Knight
shifts are unchanged even across the FOT line. This shows the invariance of the spin
susceptibility in the SC state. We suggest that the origin of the FOT in magnetic field
is not ascribed to the Pauli-paramagnetic effect, but to other effects including orbital
degrees of freedom of Cooper pairs in Sr2 RuO4 .
References:
[1] H. Mukuda, K. Ishida, Y. Kitaoka, K. Miyake, Z. Mao, Y. Mori, and Y. Maeno,
Phys. Rev. B 65, 132507 (2002).
[2] S. Yonezawa, T. Kajikawa, and Y. Maeno, Phys. Rev. Lett. 110, 077003 (2013).
[3] S. Kittaka, A. Kasahara, T. Sakakibara, D. Shibata, S. Yonezawa, Y. Maeno, K.
Tenya, and K. Machida, Phys. Rev. B 90, 220502(R) (2014).
275
Tu-P048
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Knight Shift of Sr2 IrO4 in Pseudospin Singlet Superconductivity
Induced by Large Spin-Orbit Coupling
Kazutaka Nishiguchi1, Tomonori Shirakawa 2, Hiroshi Watanabe3, Ryotaro Arita4,
Seiji Yunoki1, 2, 5
1
2
Computational Condensed Matter Physics Laboratory, RIKEN, Saitama, Japan
Computational Quantum Condensed Matter Research Team, RIKEN CEMS, Saitama, Japan
3
Waseda Institute for Advanced Study, Waseda University, Tokyo, Japan
4
First-Principles Materials Science Research Team, RIKEN CEMS, Saitama, Japan
5
Computational Materials Science Research Team, RIKEN AICS, Hyogo, Japan
5d transition metal oxide Sr2 IrO4 has been focused both experimentally and
theoretically because of the unexpected properties and novel phenomena arising from
not only its electron correlation but also highly entangled spin and orbital degrees of
freedom due to the large spin-orbit coupling (SOC). Several experiments have revealed
that an antiferromagnetic insulating state appears at low temperatures, and very recently,
a pseudogap-like structure has been observed experimentally in the electron-doped
Sr2 IrO4 , whose properties are analogous to high-Tc cuprates. On the other hand, some
theoretical studies have proposed that pseudospin singlet pairing superconductivity is
favored due to the large SOC once mobile carriers are introduced. To reveal such an
exotic superconducting (SC) state, especially, nuclear magnetic resonance (NMR) is
considered to be important because NMR experiment enables us to obtain the
information about SC states. Thus the theoretical studies of the experimental responses
of the pseudospin singlet pairing are still awaited.
To understand the effects of the large SOC on NMR experiments for carrier-doped
Sr2 IrO4 , we have investigated an effective t2g three-orbital Hubbard model on the
square lattice with a large SOC. In this study, based on the linear response theory, we
first derive the theoretical expression for the Knight shift in the presence of the large
SOC, and then we analytically and numerically study the dynamical correlation
functions related to the Knight shift in a normal and SC state. We here assume that dx2y2- and s±-wave pseudospin singlet pairing are favored in carrier-doped Sr2 IrO4 . We
derive an analytical expression for the spin susceptibility from the BCS Hamiltonian
with the SOC. We also numerically calculate some dynamical correlation functions
related to the Knight shift with the random phase approximation. Our results show that
the Knight shift in the presence of the large SOC decreases below Tc but does not go
to zero at T=0. We also find that its low-T behavior for the dx2-y2-pairing is linear,
whereas that for the s±-wave pairing is exponential.
Reference:
[1] H. Watanabe, T. Shirakawa, and S. Yunoki, Phys. Rev. Lett. 110, 027002 (2013).
[2] K. Nishiguchi, H. Watanabe, and S. Yunoki, JPS Conf. Proc. 3, 015037 (2014).
[3] K. Nishiguchi, T. Shirakawa, H. Watanabe, R. Arita, and S. Yunoki, (in
preparation).
276
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Sr2 RuO4 at high uniaxial strain
Alexander Steppke1, Lishan Zhao1,2, Clifford Hicks1, Daniel Brodsky1,2, Mark
Barber1,2, Alexandra Gibbs3, Yoshiteru Maeno4, Andrew Mackenzie1,2
1
2
University of St Andrews, UK
3
Max Planck Institute for Solid State Research, Stuttgart, Germany
4
Kyoto University, Japan
We applied high anisotropic strains to high-quality single crystals of the
superconductor Sr2 RuO4 , to gain information on the influence of anisotropic Fermi
surface distortions on its superconductivity. Due to proximity to a van Hove singularity,
one of the Fermi surfaces distorts particularly strongly in response to anisotropic strain
[1]. The superconducting properties also vary strongly: we show susceptibility and
resistivity data indicating that Tc more than doubles as strain is applied, and passes
through a sharp peak. Similarly, the upper critical field Hc2 for fields both parallel and
perpendicular to the crystallographic c axis increases substantially. For fields
perpendicular to the c axis, there is strongly hysteretic behavior at low temperatures,
that may be due to Pauli limiting.
Reference:
[1] C. W. Hicks et al., Science 344, 283 (2014)
277
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Superconductivity mediated by polar phonons in 𝐒𝐫𝐓𝐢𝐎𝟑
S. E. Rowley1,2,, C. Enderlein1,2, J. Oliveira1,3, F. Dinóla-Neto2,4, S. S. Saxena2, G. G. Lonzarich2
and E. Baggio-Saitovitch1
1
2
Centro Brasileiro de Pesquisas Físicas, MCTI, Rio de Janeiro, Brazil;
Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE,
England;
3
4
Universidade Estadual do Rio De Janeiro, Rio de Janeiro, Brazil;
Uninorte, Rua Huascar de Figueiredo 290, Centro, Manaus, Amazonas, Brazil
Weakly electron doped SrTiO3 is well known as the most dilute superconductor.
The mere fact that superconductivity occurs at charge carrier densities at least as low
as 1017 /cm3 can be seen as proof of an exorbitant interaction strength generating an
attractive force between the electrons. Thus, although the material exhibits a critical
temperature of approximately 1 K or less, it is of great interest in the search for
superconductors with higher transition temperatures. Here, we present a combined
experimental and theoretical work, which clearly demonstrates that polar optical
phonons might act as the glue between electrons. Our measurements of Tsc under
pressure shows a behaviour that agrees very well with the predictions of our theory of
electron pairing via polar modes that exist close to a ferroelectric quantum critical point.
These results provide routes to discovering new superconductors that exhibit the same
or similar pairing mechanisms.
278
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Magnetic and electric properties of the Laves Phases La2CoAl3
and Ce2CoAl3
Jenq-Wei Chen1, Ding-En LIn1, Wei-Yi Yu1, G. Narsinga Rao1
1
Department of Physics, National Taiwan University, Taipei, Taiwan, R. O. C.
We investigated the crystal structure, electrical, and magnetic properties of the Laves
phase R2CoAl3(R = La and Ce) using the powder X-ray diffraction, ac electrical
resistivity ρ, and magnetic susceptibility χ measurements. Powder X-ray diffraction
patterns reveal that both samples crystallize in the MgCu2 -type structure with space
group Fd-3m The obtained values of the lattice parameters are a = b = c = 0.8096(1)
and 0.7970(6). nm for R = La and Ce, respectively. The occurrence of diamagnetic
transition in the χ(T) curve and a drop off in the ρ (T) curve to zero value at ~5.8 K
indicate that La2CoAl3 becomes cuperconducting for T < 5.8 K. The isothermal
magnmetization curve at T = 2 K reveals that La2CoAl3 is a type II superconductor.
The appearance of a peak at ~ 10 K in the (T) curve indicates that Ce2CoAl3 is
antiferromagnetic with TN = 10.1 K.
279
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Formation of Molecular-Orbital Bands in a Twisted Hubbard Tube:
Implications for Unconventional Superconductivity in K2Cr3As3
Hanting Zhong,1Xiao-Yong Feng,1,2,* Hua Chen,3,4 and Jianhui Dai1,2,†
1Condensed Matter Group, Department of Physics, Hangzhou Normal University,
2Hangzhou Key Laboratory of Quantum Matter, Hangzhou Normal University, Hangzhou
310036, China
3International Center for Quantum Materials and School of Physics, Peking University,
Beijing 100871, China
4Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
We study a twisted Hubbard tube modeling the [CrAs]∞ structure of quasi-onedimensional superconductors A2Cr3As3(A=K,Rb,Cs).The molecular -orbital bands
emerging from the quasi-degenerate atomic orbitals are exactly solved. An effective
Hamiltonian is derived for a region where three partially filled bands intersect the Fermi
energy. The deduced local interactions among these active bands show a significant
reduction compared to the original atomic interactions. The resulting three-channel
Luttinger liquid shows various interaction-induced instabilities including two kinds of
spin-triplet superconducting instabilities due to gapless spin excitations, with one of
them being superseded by the spin-density-wave phase in the intermediate Hund’s
coupling regime. The implications of these results for the alkali chromium arsenides
are discussed.
Reference:
[1]. J.-K. Bao et al., Phys. Rev. X 5, 011013 (2015).
[2]. Z.-T. Tang, J.-K. Bao, Y. Liu, Y.-L. Sun, A. Ablimit, H.-F.Zhai, H. Jiang, C.-M. Feng, Z.-A. Xu,
and G.-H. Cao, Phys.Rev. B 91, 020506(R) (2015).
[3]. Z.-T. Tang, J.-K. Bao, Z. Wang, H. Bai, H. Jiang, Y. Liu,H.-F. Zhai, C.-M. Feng, Z.-A. Xu, and
G.-H.Cao, Sci.China Mater. 58, 16 (2015).
[4]. H. Jiang, G. Cao, and C. Cao, Sci. Rep. 5, 16054 (2015).
[5]. X. Wu, C.-C. Le, J. Yuan, H. Fan, and J.-P. Hu, Chin. Phys.Lett. 32, 057401 (2015).
[6]. H. Z. Zhi, T. Imai, F. L. Ning, J.-K. Bao, and G.-H. Cao,Phys. Rev. Lett. 114, 147004 (2015).
[7]. G. M. Pang, M. Smidman, W. B. Jiang, J. K. Bao, Z. F.Weng, Y. F. Wang, L. Jiao, J. L. Zhang,
G. H.Cao, and H. Q. Yuan, Phys. Rev. B 91, 220502(R) (2015).
[8]. W. Wei, J. Cheng, K. Matsubayashi, P. Kong, F. Lin, C. Jin,N. Wang, Y. Uwatoko, and J. Luo,
Nat.Commun. 5, 5508(2014).
[9]. H. Kotegawa, N. Nakahara, H. Tou, and H. Sugawara,J. Phys. Soc. Jpn. 83, 093702 (2014).
[10]. Y. Zhou, C. Cao, and F. C. Zhang, arXiv:1502.03928.
[11]. X. Wu, F. Yang, C. Le, H. Fan, and J. Hu, Phys. Rev. B 92,104511 (2015).
[12]. J. Solyom, Adv. Phys. 28, 201 (1979).
[13]. T. Giamarchi, Quantum Physics in One Dimension (Oxford University Press, Oxford, UK, 2003).
[14]. E. Arrigoni, Phys. Lett. A 215, 91 (1996).
[15]. H.-H. Lin, L. Balents, and M. P. A. Fisher, Phys. Rev. B 56,6569 (1997).
[16]. Y. A. Krotov, D.-H. Lee, and S. G. Louie, Phys. Rev. Lett.78, 4245 (1997).
280
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High Magnetic Field Study of Pressure-induced Superconductor
CrAs
Qun Niu1, K. Y. Yip1, W. C. Yu1, H. Kotegawa2, H. Sugawara2, H. Tou2, S. K. Goh1
1
Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories,
Hong Kong, China
2
Department of Physics, Kobe University, Kobe 658-8530, Japan
Recently, superconductivity is observed in CrAs single crystal above a critical
pressure pc ~ 0.7 GPa, where the helimagnetic transition is completely suppressed. As
pressure increases beyond pc, both the upper critical field and the temperature
coefficient A in the resistivity decrease [1,2]. We study the magnetoresistance (MR) of
CrAs as a function of pressure up to 14 T at temperature as low as 15 mK, and calculate
its bandstructure using density functional theory. The pressure evolution of MR will be
presented and its implications will be discussed in the context of quantum criticality of
the system.
Reference:
[1] H. Kotegawa et al., Journal of the Physical Society of Japan 83, 093702 (2014)
[2] W. Wu et al., Nature communications 5, 5508 (2014)
281
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Impurity Effect on Superconducting Transition Temperature in
K 2 Cr3 As3
Y. Liu1,2 , J. K. Bao1,2 , A. Ablimit1,2 , Z. T. Tang1,2 , H. F. Zhai1,2 , P. Zhang1,2, G. H. Cao1,2,3*
1
2
Department of Physics, Zhejiang University, Hangzhou 310027, China;
Collabortative Innovation Center of Advanced Microstructures, Nanjing 210093, China;
3
State Key Lab of Silicon Materials, Zhejiang University, Hangzhou 310027, China
Impurity scattering is an important probe for detecting superconducting properties.
Here we report the impurity effect on superconducting transition temperature 𝑇𝐶 in the
newly discovered Cr-based superconductor K 2 Cr3 As3 [1]. We find that the apparent
weak sensitivity of T𝐶 to the residual resistivity is due to the fact that the samples are
mostly in a clean limit. We also demonstrate that both magnetic and nonmagnetic
impurities suppress the 𝑇𝐶 , basically following the generalized Abrikosov-Gorkov
pair-breaking theory. The result suggests a non-s-wave superconducting order
parameter for K 2 Cr3 As3 .
Reference:
[1] J. K. Bao et al., PRX 5, 011013 (2015).
282
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Electronic structure of quasi-one-dimensional K 𝑥 Cr3 As3 from
first-principles
Hao Jiang2, Guanghan Cao2, Jianhui Dai1, Chao Cao1
1
Department of Physics, Hangzhou Normal University, Hangzhou, China
2
Despite of their similar composition and structure, the quasi-one-dimensional
K 2 Cr3 As3 and KCr3 As3 exhibit quite different physical properties. By performing
first principles calculations on these materials, we discover that the ground state of
K 2 Cr3 As3 is paramagnetic with one 3D Fermi surface sheet and two quasi-1D sheets.
Despite of the relatively small atomic numbers, the antisymmetric spin-orbit coupling
splitting is sizable (≈60 meV) on the 3D Fermi surface sheet as well as on one of the
quasi-1D sheets. The imaginary part of bare electron susceptibility shows large peaks
at Γ, suggesting the presence of large ferromagnetic spin fluctuation in the compound.
For KCr3 As3 , the ground state is interlayer antiferromagnetic. The magnetic Fermi
surface involves 3 one-dimensional sheets only, manifesting the reduced
dimensionality. By fitting a twisted spin tube model, the magnetic frustrations are found
to be relaxed, leading to gapless spin excitations. A frustration-induced transition to the
disordered low block-spin state is expected upon increasing the intralayer exchange
interaction.
Reference:
[1] Hao Jiang et al., Sci. Rep. 5, 16054 (2015)
[2] Chao Cao et al., Phys. Rev. B 92, 235107 (2015)
283
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Second-Order Structural Transition in Superconductor La3Co4Sn13
Yiu Wing Cheung1, Y. J. Hu1, J. Z. Zhao1, J. Y. Zhu1, W. C. Yu1, M. Imai2,
K. Yoshimura2,3, S. K. Goh1
1
Department of Physics, The Chinese University of Hong Kong, China
Department of Chemistry, Graduate School of Science, Kyoto University, Japan
3
Research Center for Low Temperature and Materials Sciences, Kyoto University, Japan
2
The family of the superconducting quasiskutterudite with general chemical formula
R3T4Sn13 (R = Ca, Sr; T = Rh, Ir) was recently found to feature a structural transition at
T*, which can be tuned to a structural quantum critical point by chemical and/or
physical pressure, around which a dome-shaped variation of the superconducting
transition temperature Tc is found [1-3]. Similar behavior was found in the isostructural
compound La3Co4Sn13 [4], although there is currently a dispute in the literature
regarding the nature of T* transition [5,6]. To shed light on the interplay of structural
instability and superconductivity, we measure the resistivity and specific heat of
La3Co4Sn13, focusing particularly on their temperature dependence around T*. Our
results, in combination with lattice dynamics calculations, are more consistent with the
second-order nature of the phase transition at T*.
Reference:
[1] L. E. Klintberg et al., Phys. Rev. Lett. 109, 237008 (2012)
[2] S. K. Goh et al., Phys. Rev. Lett. 114, 097002 (2015)
[3] W. C. Yu, Y. W. Cheung et al., Phys. Rev. Lett. 115, 207003 (2015)
[4] A. Ślebarski et al., Phys. Rev. B 89, 125111 (2014)
[5] H. F. Liu et al., Phys. Rev. B 88, 115113 (2013)
[6] P. Neha et al., J. Alloys Compd. (In Press, 2016)
284
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Optical study of the charge density wave order in Sr3 Rh4 Sn13 and
(Ca0.5 Sr0.5 )3 Rh4 Sn13
W. J. Ban1, H. P. Wang1, C. W. Tseng2, C. N. Kuo2, C. S. Lue2, N. L. Wang3
1
Institute of Physics, Chinese Academy of Sciences, Beijing
Department of Physics, National Cheng Kung University, Tainan, Taiwan
3
2
(Ca1−𝑥 Sr𝑥 )3 Rh4 Sn13 belongs to a family with Yb3 Rh4 Sn13 -type structure showing
interesting coexistence of structural phase transition and superconductivity. The
structural phase transition leads to the formation of a superlattice modulation, which
has a lattice parameter twice of that in the high temperature phase. It has been further
argued that this superlattice transition is associated with a charge density wave (CDW)
transition of the conduction electron system. We perform optical spectroscopy
measurements across the structural phase transition on single-crystal samples of
Sr3 Rh4 Sn13 and (Ca0.5 Sr0.5 )3 Rh4 Sn13 . Clear energy gap formation were observed for
both single-crystal samples when they undergo the charge-density wave transitions. The
existence of a Drude component in optical conductivity below T𝐶𝐷𝑊 indicates that the
Fermi surface is only partially gapped in the CDW state. The obtained 2Δ/(k 𝐵 T𝐷𝑊𝐶 )
values are roughly 13 for Sr3 Rh4 Sn13 and 20 for (Ca0.5 Sr0.5 )3 Rh4 Sn13 , respectively.
The values are considerably larger than the mean-field value based on the weakcoupling BCS theory. The observed spectral features in (Ca1−𝑥 Sr𝑥 )3 Rh4 Sn13 resemble
to those seen in many other CDW systems.
285
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Effect of atomic disorder and Ce doping on superconductivity of
skutterudite-related Ca3Rh4Sn13
A. Ślebarski1, J. Goraus1, M. M. Maśka1, P. Witas1, M. Fijałkowski 1, M. B. Maple2
2
1Institute of Physics, University of Silesia, Katowice, Poland
Department of Physics, University of California, San Diego, La Jolla, California, USA
Ca3Rh4Sn13 has been reported to be a paramagnetic compound and superconductor
with Tc ≈ 8.4 K. However, the superconducting state of this material was proposed [1]
to be strongly dependent on the atomic disorder which, when is quenched, leads to
strong decreasing of Tc. On the other hand, there are known examples of analogous
skutterudite-related superconductors (La3Rh4Sn13, La3Ru4Sn13[2]) which show
evidence of nanoscale disorder over length scale similar to the coherence length as a
bulk property, leading to an inhomogeneous superconducting state with the critical
temperature Tc* > Tc. This behavior has also been observed in other strongly correlated
f -electron superconductors and, we believe, will attract future attention. With this
motivation we present the magnetic and electrical transport investigations of
Ca3Rh4Sn13 doped with Ce. The Ce-doping drives Ca3Rh4Sn13 through a Tc vs x
superconducting dome between x = 0 and ~0.8, similar to that documented for high-Tc
cuprates, and forms a spin-glass-like phase in coexistence with superconducting one.
The superconductivity is enhanced by this magnetic state from Tc = 4.8 K for the parent
sample to ~8 K for Ca2.8Ce0.2Rh4Sn13. For Ca3Rh4Sn13 the measured negative dρ/dP
value of the resistivity ρ change under pressure P well correlates with the calculated
decrease of the density of states (DOS) at the Fermi energy vs P. Basing on our band
structure calculations performed vs pressure, we demonstrate how the change of DOS
would change Tc of Ca3Rh4Sn13 under various lattice pressure, when the sample is
strongly defected by quenching. The resistivity, specific heat and susceptibility data
suggest in the system of Ca3-xCexRh4Sn13 compounds (x < 0.8) a granular
superconductivity, a form of inhomogeneous superconductors.
Reference:
[1]J. P. A. Westerveld et al., J. Phys. F: Met. Phys. 17, 1963 (1987).
[2]A. Ślebarski et al., Phys. Rev. B 89, 125111 (2014)
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Superconductivity in the new cubic strongly correlated compound
Yb3Pd4Sn13
R.F. Djoumessi1, A.M. Strydom1, F. Gastaldo2, I. Čurlík3, M. Reiffers3, and M. Giovannini2
1
Highly Correlated Matter Research Group, Physics Department, University of Johannesburg,
PO Box 524, Auckland Park 2006, South Africa
2
Department of Chemistry, University of Genova, Via Dodecaneso 31, 1-16146 Genova, Italy
3
Faculty of Humanities and Natural Sciences, University of Prešov, 17. novembra 1, SK 081
16 Prešov, Slovakia
The cubic ternary intermetallic system with nominal stoichiometry R3T4X13 forms
most commonly with rare-earth elements R, d-electron elements T, and p-electron
elements X=Sn and Ge. It has presented an exceptionally profitable study field for
cooperative phenomena such as superconductivity and magnetic order, as well as
electron correlation and the heavy fermion ground state. As part of a study into Yb-PdSn phases, we demonstrate here that Pd is also adopted as a d-electron element in the
R3T4X13 structure. We report on the synthesis and crystal structure analysis of the
compound Yb3Pd4Sn13. The magnetic susceptibility at intermediate temperatures
indicate that Yb is in the magnetic trivalent state, but with a strongly reduced effective
magnetic moment compared to the free-ion Yb3+ value. The compound is found to
become superconducting below 3K, with clear superconducting phase transition
anomalies consistently found in the magnetic susceptibility, electrical resistivity, and
specific heat. However, the superconducting phase transition is superimposed upon a
large and temperature-dependent background of heat capacity. When viewing the
electronic specific heat as Cp(T)/T, this reaches 700 mJ/mol•K2 at 0.4 K, following a
power-law divergence that persists up to 4 K. We discuss the field dependencies of the
superconductivity and the low-temperature specific heat.
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NMR studies of coexistence of superconductivity and CDW in
LaPt2Si2
T. Aoyama1, T. Kubo1, H. Matsuno1, H. Kotegawa1, H.Tou1, A. Mitsuda2, Y. Nagano2, N.
Araoka2, Y. Wada2, Y. Yamada3
1
2
Department of physics, Kobe University, Kobe, Hyogo
Departmentofphysics,Kyushu University, Hukuoka 8190395,Japan
3
Department of physics, Niigata University, Niigata 950-2181
LaPt2Si2 exhibits a structural transition at around 110K and a superconductivity at
around Tc=2K. The structural transition is expected to be a formation of a charge density
wave (CDW) with CDW nesting vector 𝐪𝑪𝑫𝑾 =(1/3,0,0) or (2/3,0,0) from various
measurements, electron resistivity, magnetic susceptibility, XRD and SAED for a
polycrystalline LaPt2Si2. Thus the superconductivity of LaPt2Si2 is expected to be
coexistence with CDW state. LaPt2Si2 has two types of Pt2Si2 layers, [Pt2Si2] layers
consisting of PtSi4 tetrahedra and [Si2Pt2] layers consisting of SiPt4 tetrahedra. The
band calculations by S. Kim et al and H. Hase et al point out the CDW occurs in [Pt2Si2]
layers. In order to investigate the CDW state in LaPt2Si2, we have carried out 195PtNMR and 139La-NMR for single crystalline. Present our NMR results strongly suggest
that [Si2Pt2] layers are normal metal at all temperature and the partial density of states
in [Pt2Si2] layers decreases below 110K.
References:
[1] Y. Nagano, N. Araoka, A. Mitsuda, H. Yayama, H. Wada, M. Ichihara, M. Isobe
and Y. Ueda, J.Phys. Soc. Jpn. 82, 064715 (2013).
[2] S. Kim, K. Kim and B. I. Min Sci Rep. 2015:vol5:15052.
[3] Hase, T. Yanagisawa, Physica C 484, 59 (2013).
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Interplay between multiple charge-density waves and the
relationship with superconductivity in Pd3HoTe3
Rui Lou1, 2, Yipeng Cai1, 2, Zhonghao Liu3, Tian Qian4, Lingxiao Zhao4, Yu Li5, Kai Liu1, 2,
Zhiqing Han1, 2, Dandan Zhang1, 2, Junbao He4, Genfu Chen4, 6, Hong Ding4, 6, Shancai Wang1,
2
1
Department of Physics, Renmin University of China, Beijing 100872, China
Beijing Key Laboratory of Opto-electronic Functional Materials & Micro-nano Devices,
Renmin University of China, Beijing, China
3
Institute for Solid State Research, IFW Dresden, Dresden 01171, Germany
4
5
Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA
6
2
HoTe3 , a member of the rare-earth tritelluride (RTe3 ) family, and its Pd-intercalated
compounds, PdxHoTe3, where superconductivity (SC) sets in as the charge-density
wave (CDW) transition is suppressed by the intercalation of a small amount of Pd, are
investigated using angle-resolved photoemission spectroscopy (ARPES) and electrical
resistivity. Two incommensurate CDWs with perpendicular nesting vectors are
observed in HoTe3 at low temperatures. With a slight Pd intercalation (x = 0.01), the
large CDW gap decreases and the small one increases. The momentum dependence of
the gaps along the inner Fermi surface (FS) evolves from orthorhombicity to near
tetragonality, manifesting the competition between two CDW orders. At x = 0.02, both
CDW gaps decreases with the emergence of SC. Further increasing the content of Pd
for x = 0.04 will completely suppress the CDW instabilities and give rise to the maximal
SC order. The evolution of the electronic structures and electron-phonon couplings
(EPCs) of the multiple CDWs upon Pd intercalation are carefully scrutinized. We
discuss the interplay between multiple CDW orders, and the competition between CDW
and SC in detail.
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Interplay between Time Reversal Symmetry Breaking and
Superconducting Transition Temperatures in La-doped Filled
Skutterudite Superconductors Pr1−𝑥 La𝑥 Pt 4 Ge12
Jian Zhang1, K. Huang1, Z. F. Ding1, C. Tan1, A. D. Hillier2, and Lei Shu1,3
1
State Key Laboratory of Surface Physics, Department of Physics, Fudan University, Shanghai,
China
2
ISIS facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation
Campus, Chilton, Didcot, Oxon. UK
3
Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai,
China
Zero-field muon spin relaxation measurements were performed on La-doped filled
skutterudite superconductors Pr1−𝑥 La𝑥 Pt 4 Ge12 (x = 0.3, 0.5, 0.7, 0.9) to investigate
the effect of La doping on broken time reversal symmetry (TRS) in the superconducting
state. These alloys have very close superconducting transition temperatures (Tc),
varying from ~ 7.8K to ~ 8.1 K. Broken TRS in them is signaled by the onset of a
spontaneous static local magnetic field Bs below Tc with an amplitude of ~1 G.
Different from their isostructural Pr1−𝑥 La𝑥 Pt 4 Ge12 and Pr1−𝑥 Ce𝑥 Pt 4 Ge12 alloy
series which both exhibit the proportional decrease of Bs with the decrease of Pr
concentration, broken TRS was found to vanish suddenly with x ~ 0.9 in
Pr1−𝑥 La𝑥 Pt 4 Ge12 .
*More heat capacity measurement results and discussions will be presented.
Reference:
[1] M. Sigrist and K. Ueda, Rev. Mod. Phys. 63, 239 (1991).
[2] A. Maisuradze, et al, Phys. Rev. B 82, 024524 (2010).
[3] L. Shu, et al, Phys. Rev. B 83, 100504(R) (2011).
[4] R. Gumeniuk, et al, Phys. Rev. Lett. 100, 017002 (2008).
[5] A. Maisuradze, et al, Phys. Rev. B 103, 147002 (2009).
[6] Y. Aoki, et al, Phys. Rev. Lett. 91, 067003 (2003).
[7] J. Zhang, et al, Phys. Rev. B 91, 104523 (2015)
[8] J. L. Zhang, et al, Phys. Rev. B 92, 220503(R) (2015)
290
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Broken time-reversal symmetry probed by muon spin relaxation in
the caged type superconductor Lu5Rh6Sn18
A.Bhattacharyya,1, 2 D.T. Adroja,1, 2 J. Quintanilla,1, 3 A. D. Hillier,1 N. Kase,4 A.M. Strydom,2
and J. Akimitsu4
1
2
ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot Oxon, OX11 0QX, UK
Highly Correlated Matter Research Group, Physics Department,University of Johannesburg, PO
Box 524, Auckland Park 2006, South Africa
3
SEPnet and Hubbard Theory Consortium, School of Physical Sciences, University of Kent,
Canterbury CT2 7NH, UK
4
Department of Physics and Mathematics, Aoyama-Gakuin University,Fuchinobe 5-10-1,
Sagamihara, Kanagawa 252-5258, Japan(Dated: January 14, 2016)
It is a major theoretical challenge in strongly correlated electron systems to understand the pairing
mechanism in unconventional superconductors [1, 2]. In conventional `s wave' superconductors,
only gauge symmetry is broken. If the pairing is not conventional then some other symmetries of
the Hamiltonian may be broken below the super-conducting transition. Symmetries which might be
broken include lattice point and translation group operations and spin rotation symmetries, in
addition to the global gauge symmetry that is responsible for the Meissner effect, flux quantization,
and the Josephson effects. The nature of the broken symmetry in the pairing state is reflected in the
symmetry properties of the order parameter. Superconductors whose crystal structure features a
center of inversion, can be classified via the parity of Cooper pair state: the spin-singlet pair state
(S = 0) corresponds to an orbital pair wave function Ψ(k)~Ψ(-k) with even parity [i.e., Δ(k) = Δ(k)]; The spin-triplet state (total spin S = 1) has a superconducting order parameter with odd
parity[Ψ(k) ~ -Ψ (-k)] [3]. A few compounds have been reported to be spin-triplet superconductors,
for example the 4d-electron system Sr2RuO4, and the 5f-electron systems UPt3 and UNi2Al3.
Caged type structures have received considerable attention due to their fascinating properties [4].
Three cage compounds have been comprehensively studied over the past decade as “rattling-good"
materials: Ge/Si clathrates, lled skutterudites (RT4X12), and pyrochlore oxides (AOs2O6) [4].
Usually they possess three dimensional skeletons encompassing large atomic cages, inside of which
moderately small atoms are positioned and can “rattle" with large atomic excursions owing to the
virtual size discrepancy, weak structural coupling, and strong electron phonon (rattler) coupling,
leading to a substantial anharmonicity for rattling vibration. For instance, rattling of the A atoms in
the OsO6 cages induce extremely strong-coupling superconductivity in AOs2O6. A strong interplay
between quadrupolar moment and superconductivity has been pointed out in RT4X12 and RT2X20.
R5Rh6Sn18 (R = Sc, Y, Lu), which can also be categorized as the cage compounds, exhibit
superconductivity with the transition temperature Tc = 5 K (Sc), 3 K (Y), and 4 K (Lu). These
compounds have a tetragonal structure with the space group I41/acd and Z = 8, where R occupies
two sites of different symmetry.
The superconducting state of the caged type compound Lu5Rh6Sn18 has been investigated by
using magnetization, heat capacity, and muon-spin relaxation or rotation (μSR) measurements [57]. Our zero- field μSR measurements clearly reveal the spontaneous appearance of an internal
magnetic eld below the transition temperature, which indicates that the superconducting state in this
material is characterized by the broken time-reversal symmetry. Further the analysis of temperature
dependence of the magnetic penetration depth measured using the transverse field μSR
measurements suggest an isotropic s-wave character for the superconducting gap. This is in
agreement with the heat capacity behavior and we show that it can be interpreted as in terms of an
non unitary triplet state with point nodes and an open Fermi surface.
Reference:
[1].
[2].
[3].
[4].
[5].
J. Bardeen, L. N. Cooper, and J. R. Schrie er, Phys. Rev. 108, 1175 (1957).
M. Sigrist and K. Ueda, Rev. Mod. Phys. 63, 239 (1991).
C. Tsuei and J. R. Kirtley, , Rev. Mod. Phys. 72, 969 (2000).
Z. Hiroi, J. Yamaura, and K. Hattori, J. Phys. Soc. Jpn. 81, 011012 (2012).
Bhattacharyya, D.T. Adroja, J. Quintanilla, A. D. Hillier, N. Kase, A.M. Strydom, and J. Akimitsu,
Phys. Rev. B 91, 060503(R) (2015).
[6]. Bhattacharyya, Devashibhai Adroja, Naoki Kase, Adrian Hillier, Jun Akimitsu and Andre
Strydom, Scienti c Reports 5, Article number: 12926 (2015).
[7]. D. T. Adroja, A.Bhattacharyya, M. Telling, Yu. Feng, M. Smidman, B. Pan, J. Zhao, A. D. Hillier,
F. L. Pratt, and A. M. Strydom Phys. Rev. B 92, 134505 Published 8 October 2015
291
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Superconductivity in noncentrosymmetric La4RuAl
Y. F. Wang1, M. Smidman1, C. Y. Guo1, B. Shen1, Z. F. Weng1,G. M. Pang1 ,W. B. Jiang1,
Y. J. Zhang1, H. Lee1 , H. Q. Yuan1,*
1.
Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou
310058, China
We have synthesized polycrystalline La4RuAl by arc-melting, which belongs to a
large family of noncentrosymmetric intermetallic compounds. After annealing, the
crystal structure and composition were characterized using x-ray diffraction and
energy-dispersive x-ray spectroscopy. Our results indicate that La4RuAl is a
noncentrosymmetric superconductor with a Tc of 1.8K, which is confirmed by
resistivity and specific heat measurements. The zero temperature upper critical field
Hc2(0) is estimated to be 1.2T, which is below the Pauli limit, while the temperature and
field dependence of the specific heat is consistent with a fully opened gap. This suggests
that at present there is not yet evidence for significant singlet-triplet mixing in this
system, arising from the effects of the antisymmetric spin-orbit coupling.
292
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Odd-parity superconductivity in transition metal dichalcogenides
Y. Nakamura1, and Y. Yanase2
1
Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan
2
Since the discovery of the non-centrosymmetric superconductor CePt3Si[1], novel
physical prop-erties arising from broken inversion symmetry are attracting interest.
This subject has been extended to so-called locally non-centrosymmetric
superconductivity. For instance, the superconductivity in multi-layer systems is subject
to various study, and some novel superconducting phases have been dis-covered. The
pair-density wave (PDW) state, in which order parameter shows phase shift between
two outer layers is one of those superconducting phases[2]. As shown by previous
research[2,3], when anti-symmetric spin-orbital coupling(ASOC) is lager than an inter
layer hopping, the inhomogeneous the Rashba-type ASOC stabilizes PDW state in the
high magnetic field region.
Transition metal dichalcogenide (TMDC) has been attracting widespread attention
as novel two dimensional materials. Recently, it was reported that TMDC’s surface
becomes superconducting by electron doping with using the electric-double-layer
transistor[4,5,6]. It has been shown that a few layer contribute to the
superconductivity[5,7]. Interestingly, monolayer TMDC is lacking inversion center in
the crystal structure, which is represented by D3h point group symmetry. In this case,
the Zeeman-type ASOC arising from the intrinsic inversion symmetry breaking gives
rise to a high critical magnetic field beyond paramagnetic limit[7]. On the other hand,
the point group of bi-layer TMDC is D6h, and then the system is centrosymmetric, but
the local symmetry of transition metal ions remains to be D3h. We propose an exotic
superconducting state induced by this locally non-centrosymmetric structure in bi-layer
TMDC.
We find that the staggered Zeeman-type ASOC arising from the local violation of
inversion symmetry stabilizes an odd-parity PDW state in high magnetic field region.
In this system, an inter layer hopping is linearly decreased as it approaches the K and
K’ point because of the non-symmorphic crystal structure of bulk TMDC. Then, the
ASOC significantly affects the superconducting state and stabilizes the PDW state. We
also show the rules of Rashba-type ASOC and Josephson vortex on the phase diagram.
References
[1]E. Bauer, et al.: Phys. Rev Lett. 92 (2004) 027003.
[2]T. Yoshida, M. Sigrist, and Y. Yanase.: Phys. Rev. B 86 (2012) 134514.
[3]T. Watanabe, Y. Yoshida, and Y. Yanase.: arXiv 1508. 01333 (2015).
[4]J. T. Ye, et al.: Science 338, (2012) 1193.
[5]D. Costanzo, et al.: arXiv 1512. 03222(2015).
[6]W. Shi, et al.: Sci. Rep. 5 12534 (2015).
[7]Y. Saito, et al.: Nat. Phys. 3580 (2015).
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Superconductivity in magnetic multipole state
S. Sumita1 ,Y. Yanase1
1
Department of Physics, Kyoto University
In noncentrosymmetric systems, antisymmetric spin-orbit coupling (ASOC)
entangles the spin and orbital motion of electrons. Under the external magnetic field,
the Fermi surface of each helicity asymmetrically deforms. Thus, Fulde-Ferrell-LarkinOvchinnikov (FFLO) state [1, 2] may be realized. Then, the Cooper pairs are condensed
with finite center-of-mass momentum. For instance, Agterberg and Kaur discussed the
stability of magnetic-field-induced FFLO (helical) state in Rashba superconductors [3].
However, it has been shown that the helical state cannot be distinguished from a vortex
state [4].
Alternatively we propose exotic superconducting states stabilized in the antiferromagnetic or ferromagnetic state in a 1D zigzag chain which preserves global
inversion symmetry, but breaks local inversion symmetry. The antiferromagnetic
moment parallel to the g-vector of ASOC is regarded as magnetic quadrupole based on
the multipole expansion, while the antiferromagnetic moment perpendicular to the gvector is a magnetic monopole.
As a result of a staggered ASOC in this system, magnetic quadrupoles make the band
structure asymmetric despite the absence of the external magnetic field [5]. Therefore,
the FFLO state is stabilized at low temperatures. We demonstrate that the center-ofmass momentum of the Cooper pair continuously changes when the antiferromagnetic
moment is small, while it discontinuously changes when the moment is large.
On the other hand, we shows that the center-of-mass momentum of the Cooper pair
is zero in the magnetic monopole state. Then, the conventional Bardeen-CooperSchrieffer (BCS) state is stable. In the BCS state the order parameter is uniform in two
sublattices. On the other hand, in the magnetic dipole state (ferromagnetic state), the
pair-density wave (PDW) state [6] is stabilized. This situation resembles the
ferromagnetic superconductor UGe2. Contrary to the BCS state, the sign of the order
parameter varies between two sublattices in the PDW state.
Reference:
[1] P. Fulde and R. A. Ferrell, Phys. Rev. 135, A550 (1964).
[2] A. I. Larkin and Yu. N. Ovchinnikov, Sov. Phys. JETP 20, 762 (1965).
[3] D. F. Agterberg and R. P. Kaur, Phys. Rev. B 75, 064511 (2007).
[4] Y. Matsunaga et al., Phys. Rev. B 78, 220508 (2008).
[5] Y. Yanase, J. Phys. Soc. Jpn. 83, 014703 (2014).
[6] T. Yoshida et al., Phys. Rev. B 86, 134514 (2012).
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Nodeless superconducting gaps in noncentrosymmetric
superconductor PbTaSe2 with topological bulk nodal lines
M. X. Wang1, Y. Xu1, L. P. He1, J. Zhang1, X. C. Hong1, P. L. Cai1, Z. B. Wang1, J. K. Dong1,
and S. Y. Li1,2
1
State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of
Advanced Materials, Fudan University, Shanghai , China
2
Collaborative Innovation Center of Advanced Microstructures, Fudan University,
Shanghai , China
Low-temperature thermal conductivity measurements were performed on single
crystal of PbTaSe2, a noncentrosymmetric superconductor with topological bulk nodal
lines in the electronic band structure. It is found that the residual linear term κ0/T is
negligible in zero magnetic field. Furthermore, the field dependence of κ0/T exhibits an
S-shaped curve. These results suggest that PbTaSe2 has multiple nodeless
superconducting gaps. Therefore, the spin-triplet state with gap nodes does not play an
important role in this noncentrosymmetric superconductor with strong spin-orbital
coupling. The fully gapped superconducting state also meets the requirement of a
topological superconductor, if PbTaSe2 is indeed the case.
Reference:
[1] M. X. Wang et al., Phy. Rev. B 93, 020503(R) (2016)
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Single Crystal Growth and Superconductivity in Th7Ni3 and
La7Ni3 without Inversion Symmetry in the Crystal Structure
Ai Nakamura1, Fuminori Honda1, Yoshiya Homma1, Dexin Li1, Dai Aoki1, Kengo Nishimura2,
Masashi Kakihana2, Masato Hedo3, Takao Nakama3, and Yoshichika Ōnuki3
1Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan
2 Graduate School of Engineering and Science, University of the Ryukyus, Nishihara,
3Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan
Crystals are classified into 32 point groups. They are divided into two groups, which
are 11 centrosymmetric and 21 non-centrosymmetric groups. Typical examples are of
the so-called Rashba-type and chiral nature. In these crystal structures, an
antisymmetric spin-orbit interaction lifts not only the charge degeneracy of an electron
but also the corresponding spin. Many interesting phenomena were reported. For
example, unconventional superconductivity of CeIrSi3 with the Rashba-type structure
[1] and split Fermi surface properties in TaSi2, NbSi2, and VSi2 with the chiral crystal
structure have been observed [2].
Th7Ni3 and La7Ni3 with non-centrosymmetric hexagonal crystal structure (No. 186,
C6v4, P63mc) has shown the superconductivity at the superconducting transition
temperature Tsc=1.97 and 2.4 K, respectively [3, 4]. Th7T3 and La7T3 (T: transition
metal) are almost BCS superconductor, whereas La7Ir3 was suggested a unconventional
superconductor with spontaneous static magnetic fields and breaking time-reversal
symmetry below Tsc=2.25 K [5].
We succeeded in growing single crystals of Th7Ni3 and La7Ni3 by the Bridgman
technique, and carried out an electrical resistivity and specific heat measurement under
magnetic field. The superconductivity was observed Tsc=1.97 K in Th7Ni3 and 2.41 K
in La7Ni3 by the temperature dependences of electrical resistivity and specific heat.
The upper critical fields Hc2 are extremely high, compared to those in usual thorium
and lanthanum compounds. The unusual Hc2 might be due to the non-centrosymmetric
crystal structure. In the presentation, we will also report and discuss the results of Hc2
and field dependence of specific heat.
Reference:
[1] R. Settai et al., J. Phys. Soc. Jpn. 80, 094703 (2011).
[2] Y. Ōnuki et al., J. Phys. Soc. Jpn. 83, 061018 (2014).
[3] P. Pedrazzini et al., Physica C 336, 10 (2000).
[4] K. Ueda et al., Czech. J. Phys. 46, Suppl. S2 (1996).
[5] J. A. T. Barder et al., Phys. Rev. Lett. 115, 267001 (2015).
296
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Confinement of Superconducting Vortices in Magnetic Force
Microscopy
Jeehoon Kim1, 2
1
Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science
2
Department of Physics, Pohang University of Science and Technology
Magnetic force microscope (MFM) laboratory at CALDES in IBS has constructed a
He MFM, operating within a vector magnet with the base temperature of 300 mK and
magnetic field range of 2-2-9 T in the x-y-z direction. We demonstrated magnetic
imaging capabilities at very low temperature by imaging simultaneously
superconducting vortices and magnetic stripes at T= 500 mK in the ferromagnetic
superconductor ErNi2B2C which has a ferromagnetic transition below Twfm=2.3 K. The
direct visualization of coexistence between superconductivity and magnetism was
carried out in ErNi2B2C. The vector field performance of the apparatus was also
demonstrated by the creation and imaging of Abrikosov vortices within a
superconducting Nb film using a vector field. For example, an in-plane field allows
creating a vortex-antivortex pair which is confined through a single flux tube, and thus
showing a linear potential in distance. We show an interesting contrast of interaction
nature between confined and isolated vortices.
3
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Pd site doping effect on superconductivity in Nb2 Pd0.76 S5
C. Y. Shen1, Q. Chen1, B. Q. Si1, H. Bai1, X. J. Yang1, Q. Tao1, G. H. Cao1,2 and
Z. A. Xu1,2
1
Department of Physics and State Key Laboratory of Silicon Materials, Zhejiang University,
2
Collaborative Innovation Centre of Advanced Microstructures, Nanjing 210093, China
Recently superconductivity with Tc of about 7 K has been discovered in a transitionmetal chalcogenide Nb2PdS5, which displays extremely large upper critical field. This
compound crystallizes in a lower symmetry space-group C2/m and was argued to be a
multi-band superconductor. Here we explore the Pd site doping effect on
superconductivity in Nb2(Pd1-xRx)0.76S5 (R=Ir, Ag and Ru) by measuring resistivity,
magnetic susceptibility and Hall effect. It was found that superconducting transition
temperature (Tc) is firstly slightly enhanced by partial substitution of Pd with Ir (or Ru)
and then it is suppressed gradually as Ir (or Ru) content increases further. Meanwhile
Ag substitution quickly suppresses the system to a nonsuperconducting ground state.
Hall Effect measurements indicate the variations of charge carrier density caused by Ir
or Ag doping. The established phase diagram implies that the charge carrier density (or
the band filling) could be one of the crucial controlling factors to determine Tc in this
system. Possible competing orders are also discussed
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Evidence for nodal superconductivity in a layered compound
Ta4Pd3Te16
G. M. Pang1, W. H. Jiao2, M. Smidman1, Y. F. Wang1, C. Y. Guo1, Z. F. Weng1, W. B.
Jiang1, Y. Chen1, G. H. Cao1, and H. Q. Yuan1
1
2
School of Science, Zhejiang University of Science and Technology, Hangzhou
310023, China
Ta4Pd3Te16 is a layered compound with quasi-one-dimensional PdTe2 chains, which
becomes superconducting at Tc4.6K. [1] Band structure calculations reveal a complex
Fermi surface, including two one-dimensional nested sheets, a two-dimensional
cylindrical sheet and a three-dimensional one, which leads to the compound being an
anisotropic but three-dimensional metal. [2] The nature of the superconducting order
parameter remains controversial, with different results being obtained from different
experimental techniques. [3-6] In this presentation, we characterize the
superconducting order parameter of Ta4Pd3Te16 by measuring the temperature
dependence of the London penetration depth (T) using a tunnel-diode-oscillator
based method. Linear behavior of (T) is observed for T<<Tc, which is in contrast to
the exponential decay of conventional superconductors and suggests the existence of
low-energy excitations in the superconducting gap. A detailed analysis shows that the
superfluid density s(T) can be well described by a phenomenological two-band s+d
model, which is consistent with specific heat results with similar fitting parameters.
This provides clear evidence for unconventional multi-band superconductivity in
Ta4Pd3Te16.
References
[1] W. H. Jiao, et al., J. Am. Chem.Soc. 136, 1284 (2014).
[2] D. J. Singh, Phys. Rev. B 90, 144501 (2014).
[3] J. Pan, et al., Phys. Rev. B 92, 180505(R) (2015).
[4] Z. Y. Du, et al., Sci. Rep. 5, 9408 (2015).
[5] Q. Fan, et al., Phys. Rev. B 91, 104506 (2015).
[6] W. H. Jiao, et al., J. Phys.: Condens. Matter 27, 325701 (2015).
299
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Pressure-induced superconductivity in the transition metal
dichalcogenide 1T'-MoTe2
Sangyun Lee1,Sungil Kim1, Soon-Gil Jung1,Eunsung Park1, Jihyun Kim2,
Suyeon Cho2,Sungwoong Kim2, Tuson Park1
1
2
Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea
Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Korea
We report pressure-induced superconductivity in a single crystal of the transitionmetal dichalcogenide 1T'-MoTe2. At atmospheric pressure, there occurs a resistivity
anomaly around 210 K (=T*), which was ascribed to a structural phase transition [1,2].
With increasing pressure, the transition temperature decreases and electrical resistivity
measurements do not show any anomaly associated with it above 1.2 GPa, where T*and
Tc becomes equal. The zero-resistance SC state is induced at 0.47 K for 0.4 GPa and Tc
increases with pressure. At 1.8GPa, where Tc is 3.2 K, soft-point contact spectroscopy
shows that the SC gap is 5.0meV, which is compatible with the weakly coupled BCS
value of 4.8meV. At 2.5 GPa, Tc reaches 4 K and the upper critical field Hc2 is 2.8 kOe.
The small Hc2 is ten times smaller than the Pauli limiting field, indicating that the
orbital pair breaking effects are important in MoTe2.
Reference:
[1] T. Zandt et al., J. Alloys compd. 442 216 (2007)
[2] Hughes et al., J. Phys. C: Solid State Phys. 11 L103 (1978)
[3] X. Qian, J. Liu. Fu and J. Li, Science 346, 1344 (2014).
[4] D. H. Keum et al., Nat. Phys. 11, 482 (2015).
[5] M. chhowallaet et al., Nat. Chem 5, 263 (2013).
[6] B. Radisayljevic, A. Radenovic, J. Brivio, V. Giacometti, A. Kis, Nat. Nanotech 6,
147 (2013).
[7] K. -A. N. Duerloo, Y. Li and E. J. Reed, Nat. Comm 5, 4214 (2014).
[8] J. T. Ye et al., Science 338, 1193 (2012).
[9] E. Morosan et al., Nat. Phys. 2, 544 (2006).
[10] T. Das and K. Dolui, Phys. Rev. B 91, 094510 (2015).
300
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Superconductivity in bismuth at high pressures
P. Brown1, K. Semeniuk1, F. M. Grosche1
1
Cavendish Laboratory, Cambridge University, Cambridge, UK
At pressures above 27 kbar, elemental bismuth undergoes a structural transition into
the Bi-III phase, recently determined to be a highly unusual incommensurate host-guest
structure. This structure is comprised of two distinct, interpenetrating lattices with
incommensurate c-axes. As a result the structure lacks discrete translational symmetry
– an unexpected property for an elemental crystal. Such complex structures have been
observed in a small number of other elements, but their electronic properties have not
been investigated in detail. The moderate pressures required to create the host-guest
phase in bismuth allow a rare opportunity to investigate the physical properties of these
phases.
The Bi-III phase is known to be superconducting, with a transition temperature of
around 7 K. The details of the superconducting and normal-state properties are
comparatively little explored. Here we report SQUID magnetisation and resistivity
measurements in fields up to 9 T and temperatures down to 120 mK. We find evidence
for an unexpectedly high critical field, and an unusual temperature dependence of the
resistivity in the normal state.
301
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Coherence Factors and Quantum Interferences in Excitonic
Condensation of Ta2NiSe5
Koudai Sugimoto1, Tatsuya Kaneko2, Yukinori Ohta2
1
Center for Frontier Science, Chiba University, Chiba 263-8522, Japan
2
Department of Physics, Chiba University, Chiba 263-8522, Japan
It is known that, in narrow-gap semiconductors or semimetals, pairs of electrons and
holes (excitons) are spontaneously formed and go into a condensed state with
macroscopic phase coherence. This state is referred to as an excitonic condensation [1]
and was predicted half a century ago, but actual materials of this phase is not known.
Recent angle-resolved photoemission spectroscopy experiment, however, suggested
that Ta2NiSe5 may be in the excitonic phase accompanied by the structural transition
[2]. In order to elucidate whether Ta2NiSe5 is actually in the excitonic phase or not, we
here propose measurements of ultrasonic attenuation rate and nuclear-magnetic
relaxation (NMR) rate [3].
Ta2NiSe5 has a quasi-one dimensional structure consisting of one Ni chain and two
Ta chains. In our calculation, we start with a three-chain Hubbard model describing
Ta2NiSe5 [4]. Within the self-consistent calculation in the mean-field approximation,
we obtain the ground state of the excitonic phase in this model.
Historically, the coherence factors appearing in ultrasonic attenuation rate and NMR
rate played an essential role in confirming the validity of the BCS theory of
superconductivity. We apply this concept to the excitonic phase and predict that the
quantum interference associated with the excitonic pair condensation can be seen in
these rates. In ultrasonic attenuation, constructive quantum interference exhibits a
coherence peak of this rate just below the critical temperature. In NMR, on the other
hand, destructive one leads to an abrupt reduction of the rate.
In order to see the behavior of this model at the critical temperature in more detail,
we also investigate a heat capacity and an elastic constant [3]. The heat capacity shows
a jump at this temperature, implying the second-order transition. The jump is rather
small compared to the BCS superconducting one. In the elastic constant, the softening
of the lattice corresponding to the structural transition is obtained.
The experimental confirmation of these results should be of crucial importance for
the proof that Ta2NiSe5 is really in the state of excitonic pair condensation.
Reference:
[1]D. Jérome, T. M. Rice, and W. Kohn, Phys. Rev. 158, 462 (1967).
[2]Y. Wakisaka et al., Phys. Rev. Lett. 103, 026402 (2009).
[3]K. Sugimoto et al., Phys. Rev. B 93, 041105(R) (2016).
[4]T. Kaneko et al., Phys. Rev. B 87, 035121 (2013).
302
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Anomalous local electronic states around Tl-dopant in
superconducting Pb1-xTlxTe : 125Te-NMR study
H. Mukuda1, T.Matsumura1, S. Maki1, M. Yashima1, Y. Kitaoka1, H. Murakami2, P. GiraldoGallo3, T. H. Geballe3, I. R. Fisher3
1
Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan
2
3
Institute of Laser Engineering, Osaka University, Osaka 565-0871, Japan
Department of Physics, Stanford University, Stanford, California 94305-4045, USA
Pb1-xTlxTe exhibits superconductivity when x exceeds ~0.0035. The dopant (Tl) is
known as valence skipping element, where only Tl1+ and Tl3+ are stable in ionic
compounds. Related to this character, previous experimental and theoretical studies
have suggested that valence fluctuations between 6s2(Tl1+) and 6s0(Tl3+) interpreted as
a charge Kondo effect are possible origin for the superconductivity [1-3]. It motivated
us to investigate the electronic states of this compound microscopically by 125Te-NMR
probe. Only in the superconducting sample (x=0.01), we observed anomalous large
nuclear relaxation rate (1/T1) especially at 125Te sites being close to the dopant Tl,
indicating that some kinds of dynamical electronic states appear locally around Tldopant. We will discuss the doping dependence ofthe anomalous local electronic states
in 0<x<0.01 of Pb1-xTlxTe.
Reference:
[1] Y. Matsushita, H. Bluhm, T. H.Geballe and I. R. Fisher, PRL. 94, 157002 (2005).
[2] M. Dzero and J. Schmalian, Phys. Rev. Lett. 94, 157003 (2005).
[3] H. Matsuura and K. Miyake, J. Phys. Soc. Jpn, 81, 113705(2012).
303
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Pressure tuning the Fermi-surface topology of the Weyl semimetal
NbP
Ricardo dos Reis1, M. O. Ajeesh1, Yan Sun1, S.-C. Wu1, Chandra Shekhar1, Marcus
Schmidt1, Claudia Felser1, Binghai Yan1, and Michael Nicklas1
1
The recent discovery of Weyl semimetal (WSM) in transition- metal monopnictides
brought enormous attention for this class of material due to the prediction of many
exotic phenomena, in particular, exceptional transport properties, which make these
systems not only interesting for fundamental research, but also promising materials for
novel applications. WSM can be viewed as the hybrid of “3D graphene” and topological
insulators. The band crossing point, the so-called Weyl point, acts as a magnetic
monopole (a singular point of Berry curvature) in momentum space, which always
comes in a pairs. If the time-reversal and inversion symmetries are respected, a pair of
Weyl points is degenerate in energy, forming another topological phase called Dirac
semimetal. Owing this complex band structure the details of the electronic structure can
play a significant role in the electrical transport properties of these materials. In this
context, external pressure is an important control parameter to effectively tune lattice
structures and the corresponding electronic states in a systematic fashion, avoiding the
complexity brought by chemical doping. Here, we report on the effect of pressure on
the Fermi-surface topology of the Weyl semimetal NbP by probing Shubnikov-de Haas
oscillations. Although a drastic effect on the amplitudes of the quantum-oscillations
have been observed, the frequencies remains almost unaltered to pressures up to 2.8
GPa. By comparison with band structure calculations we find that this behavior
originates from small changes in the shape of the Fermi surface. Our results
demonstrate that the study of quantum oscillations in combination with band structure
calculations provide an effective probe to investigate the pressure effects on the Fermi
surface topology in Weyl semimetals.
304
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Fermi Surface Topology of the Tantalum Mono-Pnictide Weyl
Semimetals
F. Arnold1, M. Naumann1, S.-C. Wu1, Y. Sun1, M. Schmidt1, H. Borrmann1, C. Shekhar1,
M. Nicklas1, M. Baenitz1, C. Felser1, B. Yan1,2, E. Hassinger1
1
2
Max Planck Institute for Physics of Complex Systems, Dresden
Weyl Fermions are the solution of the massless Dirac equations and have been long
sought after in high energy physics1. Weyl semimetals are the solid state realization of
these massless chiral Fermions. Recently the non-centrosymmetric mono-pnictides
(Ta,Nb)(P,As) were predicted to be Weyl semimetals by ab initio DFT calulations2.
The presence of Weyl nodes and Fermi arc surface states in these materials was later
confirmed by ARPES3.
Here we present the precise Fermi surface topology of our TaP and TaAs single
crystals with millielectronvolt Fermi energy precision as determined by quantum
oscillation measurements and ab intio bandstructure calculations. For this, angular
dependent magnetization, magnetic torque and resistivity measurements were
performed at temperatures down to 2K and magnetic fields up to 14T. Additionally,
new refined DFT bandstructures were calculated to match the observed quantum
oscillation frequencies. It will be shown that chirality in TaP is ill-defined due to a large
energy separation of the Fermi energy from the Weyl points, whereas in TaAs well
defined Weyl pockets of opposit chirality exist4. Thus special quantum phenomena due
to chirality are only expected in TaAs.
Reference:
[1] H. Weyl Zeitschrift f. Physik56, 330 (1929)
[2] H. Weng et al. Phys. Rev. X5, 011029 (2015)
[3] B. Q. Lv et al. Phys. Rev. X5, 031013 (2015),
S.-Y. Xu et al. Science349, 613 (2015)
[4] C. Shekhar et al. ArXiv:Cond-Mat1506.06577 (2015)
305
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Negative Magnetoresistance in Topological Semimetals of
Transition -Metal Dipnictides WithNontrivial Z2 Indices
Yupeng Li1,Zhen Wang1,Yunhao Lu2,Xiaojun Yang1,Zhixuan Shen1,Feng Sheng1,
Chunmu Feng1,Yi Zheng1，,Zhu-An Xu1,2
1
2
Department of Physics, Zhejiang University, Hangzhou 310027, China
State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027,
China
Negative longitudinal magnetoresistance (NLMR) caused by the Adler-Bell-Jackiw
anomaly isregarded as the most prominent quantum signature of Weyl semimetals
when electrical field E is parallel to the external magnetic field B. In this paper,
universal NLMR is reported in nonmagnetic, centrosymmetric transition metal
dipnictides MPn2 (M=Nb and Ta; Pn=As and Sb), in which Weyl fermions do not
exist. Combining temperature-dependent magnetoresistance, Hall effect and
thermoelectric coefficients of Nernst and Seebeck effects, it can be determined that the
emergence of the NLMR phenomena in each compound is related to Lifshitz transitions,
corresponding to the formation of unique electron-hole-electron (e-h-e) pockets along
the I-L-I direction. First-principles calculations suggest that, the dxy and dx2-y2
orbitals of the transition metal form a tilted nodal ring of band crossing well below
the Fermi level along the I-L line. All the crossing points are gaped by strong spinorbital coupling with nontrivial Z2 indices of[0;(111)], and the formation of the
characteristic e-h-e structure. Considering no NLMR behavior observed in pristine
WTe2 with resonant e-h pockets, the universal NLMR in the MPn2 family may have
a unique origin in the topological surface states, which appears in pairs with opposite
spin-momentum locking, rather than the bulk trivial pockets.
306
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Strong Magnetic Nonlinearity of MW and DC Resistance in Cd3As2
- Semimetal with 3D Dirac Fermions
Yu. Goryunov1, A. Nateprov2
1
E.K.Zavoisky Kazan Physical-Technical Institute of the RAS, Kazan, Russia
2
Institute of Applied Physics of the ASM, Kishenu, Moldova
It is well known [1] that for conventional conductors with a parabolic dispersion law
for current carrier, a general view of the field dependence of the magnetoresistance is
reduced to a parabolic law in weak fields and linear law into the fields higher 3 T. This
character of the field dependence in the case of conductors with Dirac fermions is
confirmed by a number of works executed on a direct current (see. e.g.[2-4]), but the
emphasis is on the linear part of the dependence. However, for single crystals at high
fields and low temperatures due to a number of well-known effects [3], this dependence
is more complex. We have scrupulously studied the shape of the field derivative of the
microwave absorption (MWA) (~ 9 GHz), magnetoresistance on direct current (MRDC)
and magnetic susceptibility (MS) in weak transverse magnetic fields up to 2 T and a
temperature of 10 - 360 K in 3D Dirac semimetal Cd3As2. The shape of the field
dependence of the MWA for the sample of powder in the dielectric matrix was strongly
non-linear (higher 2-nd order ), and its field derivative at low temperatures is yet a nonmonotonic function of the magnetic field value. In the case of a quadratic field
dependence of the MWA, it would have had a field derivative of the linear character
that is always observed in the case of usual metals. The experimental results for the
MRDC in the transverse magnetic field "too good" (deviation of less than 1%) is
described by a Δρ ~ H 4/3. When adding into the sample about 1.5 at. % of a magnetic
impurity (Eu), according to measurements of the MS in the magnetic field of 1 T at a
temperature below 110 K originaly diamagnetic Cd3As2 becomes paramagnetic and
changes the character of the nonlinearity of the field dependences. The results are
compared with previously known results for the longitudinal fields and they are
discussed in context of the role of the Fermi surface form.
Reference:
[1] P.L. Kapitza, Proc. Roy. Soc., A, 119, 458 (1928)
[2]W. Desrat, et al., J. Phys:CS, 647, 012064 (2015)
3222
[3]WU DeSheng, et al.,SCIENCE CHINA, Phys.,Mech.&Astr. 58(1), 017501(2015)
[4] Zhijun Wang, et al., PRB 88, 125427 (2013)
307
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Observation of Localized Spin States in 3D Dirac semimetal by ESR
Yu. Goryunov1, A. Nateprov2
1
2
Institute of Applied Physics of the ASM, Kishenu, Moldova
In this report we present the results of the first study electron spin resonance (ESR)
in pure and doped with europium 3D Dirac semimetal Cd3As2. We have measured Xband ESR and the field dependence of the microwave surface impedance (MSI) in
samples with different content of europium: Cd3-xEuxAs2 with x = 0; 0.075; 1.0. Study
was carried out in a temperature range of 10-350 K and magnetic fields 0 - 1 T. The
crystal structure of the samples was controlled by X-ray diffraction. For x = 0; 0.075
samples had a structure with space group I41/acd and observed a strong field
dependence of the MSI at decreasing temperature. For x = 0 on the background of a
strong dependence of the MSI on magnetic field in the temperature range 100 - 200 K,
appears weak ESR signal with a g factor ~ 2.15 and a linewidth ~ 200 Oe. For x =
0.075 above room temperature, we observed two symmetric ESR signals with
linewidth of about 150 Oe with g1 = 2.28 and g2 = 3.9. Below room temperature, is
happening a strong distortion and displacement of resonance lines to lower fields. By
lowering the temperature to 10 K, conditions of ESR observation becomes much worse
due to strong broadening and disappearance of resonant signals.
Usualy such facts testify about ordering of magnetic impurities. For sample with x =
1, the X-ray diffraction data showed a other crystal structure with space group P3ˉm1.
This composition is not Dirac semimetal and ESR measurements data (e.g., g = 2.03)
in these sample were used us to compare. The experimental results are discussed in
terms of the interaction of magnetic impurities in semimetals with Dirac fermions [1,2]
and the evolution of this interaction to the normal case of the Andersen model and
modified RKKY interaction through the usual quasiparticle (in the case of the
composition with x = 1)..
Reference:
[1] Hao-Ran Chang, et al., arXiv:1509.04741v1 [cond-mat.mes-hall] 15 Sep 2015
[2] Jin-Hua Sun, et al. arXiv:1509.05180v1 [cond-mat.str-el] 17 Sep 2015
308
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Weyl Semimetal in Heavy Fermion Systems without Inversion
Symmetry
Yohei Ibe, Masaya Nakagawa, Norio Kawakami
Department of Physics, Kyoto University, Kyoto, Japan
Recently, Weyl semimetals (WSMs) [1,2] have attracted significant interest, as an
extension of the concept of topological phase of matter with an energy gap, such as
quantum Hall systems and topological insulators (TIs), to the gapless semimetals. Since
WSMs have Weyl fermion-like energy dispersion and novel transport phenomena, such
as the anomalous Hall effect and the chiral magnetic effect, WSMs have been
intensively studied both theoretically and experimentally. However, WSMs in the
system where the electron correlation is essential have not been studied very much so
far.
On the other hand, there has been a proposal of TIs in strongly correlated f-electron
systems, named topological Kondo insulators (TKIs) [3]. TKIs have also received a lot
of attention recently, with SmB6 as a promising candidate material.
Based on these backgrounds, we propose a realization of WSM phase in a strongly
correlated f-electron system, which we call Weyl Kondo semimetals. Adopting ideas
from the model of two-dimensional topological superfluids in cold atom systems with
Rashba spin orbit coupling [4], we demonstrate the emergence of WSM phase in a
Kondo lattice system without inversion symmetry. To this end, we carry out the
calculation of the Chern number in such a system under Zeeman magnetic field and we
confirm that the system is in a WSM phase with a finite Chern number in a certain
parameter region.
We will also discuss the relation between the Kondo effect in a magnetic field and
the Rashba spin orbit coupling.
Reference:
[1] S. Murakami, New J. Phys. 9, 356 (2007)
[2] X. Wan et al., PRB 83, 205101 (2011)
[3] M. Dzero et al., PRL 104, 106408 (2010)
[4] M. Sato et al., PRL 103, 020401 (2009)
309
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Field-induced resistivity plateau and unsaturated negative
magnetoresistance in topological semimetal TaSb2
Yuke Li1, Lin Li1, Jialu Wang1, Tingting Wang1, Xuxiao Feng1, Chuanying Xi2, Chao Cao1,
Jianhui Dai1
1
Hangzhou Key lab of Quantum Matter and department of Physics, Hangzhou Normal
University, Hangzhou, China
2
High Magnetic Field Laboratory, Chinese Academy of Science , Heifei, Anhui China
Several prominent transport properties have been identified as key signatures of
topological materials. One is the resistivity plateau at low temperatures as observed in
several topological insulators (TIs); another is the negative magnetoresistance (MR)
when the applied magnetic field is parallel to the current direction as observed in several
topological semimetals (TSMs) including Dirac semimetals (DSMs) and Weyl
semimetals (WSMs). Usually, these two exotic phenomena emerge in distinct materials
with or without time reversal symmetry (TRS), respectively. Here we report the
discovery of a new member in TSMs, TaSb2, which clearly exhibits both of these
phenomena in a single material. This compound crystallizes in a base-centered
monoclinic, centrosymmetric structure, and is metallic with a low carrier density in the
zero field. While applying magnetic field it exhibits insulating behavior before
appearance of a resistivity plateau below Tc =13 K. In the plateau regime, the ultrahigh
carrier mobility and extreme magnetoresistance (XMR) for the field perpendicular to
the current are observed as in DSMs and WSMs, in addition to a quantum oscillation
behavior with non-trivial Berry phases. In contrast to the most known DSMs and
WSMs, the negative MR in TaSb2 does not saturate up to 9 T, which, together with the
almost linear Hall resistivity, manifests itself an electron-hole non-compensated TMS.
These findings indicate that the resistivity plateau could be a generic feature of
topology-protected metallic states even in the absence of TRS and compatible with the
negative MR depending on the field direction. Our experiment extends a materials basis
represented by TaSb2 as a new platform for future theoretical investigations and device
applications of topological materials.
Reference:
[1] Yuke Li et al., (2016) arXiv: 1601.02062
310
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Magnetoresistance in Weyl semimetal states emerging from weak
topological Kondo insulators
Kuninobu Sasaki1, Atsushi Tsuruta1, Takeshi Mizushima1, Satoshi Fujimoto1
1
Department of Materials Engineering Science, Osaka University
It is known that a strong topological insulator can be turned into a Weyl semimetal
when a sufficiently strong effective magnetic field applied to it closes the bulk band
energy gap. In this semimetal state, we can observe a Fermi arc connecting the pair of
Weyl points as the surface state. However, unfortunately, the Weyl semimetal state
generated in this way has not yet been experimentally observed in the realistic material.
On the other hand, it is recently proposed that the Kondo insulators CeNiSn and
CeRhSb are candidate materials for weak topological insulators, and also it has been
reported that these materials show negative magnetoresistance. Since their band gaps
are small (about 10K), it is possible to consider the scenario that they are changed into
Weyl semimetals by applying an external magnetic field and the chiral anomaly of
Weyl nodes causes the negative magnetoresistance.
Taking these points into account, we have calculated the magnetoresistance using the
effective model of a Weyl semimetal emerging from the Kondo insulators, and we will
report the result of the calculation.
Reference:
[1] A. A. Burkov et al., Phys. Rev. Lett. 107, 127205 (2011)
[2] D. Kurebayashi et al., J. Phys. Soc. Jpn. 83, 063709 (2014)
[3] T. Terashima et al., Phys. Rev. B 66, 075127 (2002)
311
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Weyl Magnon
Fei-Ye Li1, Yao-Dong Li2, Yue Yu3, Yong Baek Kim4, Leon Balents5, Gang Chen6
1
Institute of Theoretical Physics, Chinese Academy of Sciences
2
Department of Computer Sciences, Fudan University
3
Physics Department, Fudan University
4
Physics Department, Univ of Toronto, Ontario; School of Physics, Korea Institute for Advanced
Study, Seoul
5
Kavli Institute for Theoretical Physics, UCSB, California
6
Physics Department, State Key Laboratory of Surface Physics, Fudan Univ; Perimeter Institute
for Theoretical Physics
Conventional magnetic orders in Mott insulators are often believed to be trivial as
they are simple product states. In this talk, we argue that this belief is not always right.
We study a realistic spin model on the breathing pyrochlore lattice. We find that,
although the system has a magnetic ordered ground state, the magnetic excitation is
rather nontrivial and supports linear band touchings in its spectrum. This linear band
touching is a topological property of the magnon band structure and is thus robust
against small perturbation. We thus name this magnon band touching as Weyl magnon.
Just like the Weyl fermion, the existence of Weyl magnon suggests the presence of
chiral magnon surface states. Unlike the surface Fermi arcs for the Weyl fermions, the
chiral surface state for Weyl magnon appears at a finite energy due to the bosonic nature
of the magnons. Moreover, the external magnetic field only couples to the spins with a
Zeeman term and thus can readily shift the Weyl node position. This provides a way to
control the Weyl magnon. Our work will inspire a re-examination of the excitation
spectrum of many magnetic ordered systems.
312
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Detecting monopole charge in Weyl semimetals via quantum
interference transport
Xin Dai1, Hai-Zhou Lu2; , Shun-Qing Shen3, and Hong Yao1;4;
1
2
Department of Physics, South University of Science and Technology of China, Shenzhen 518055,
China
3
Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China
4
Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
Topological Weyl semimetals can host Weyl nodes with monopole charges in
momentum space. How to detect the signature of the monopole charges in quantum
transport remains a challenging topic. Here, we reveal the connection between the
parity of monopole charge in topological semimetals and the quantum interference
corrections to the conductivity. We show that the parity of monopole charge determines
the sign of the quantum interference correction, with odd and even parity yielding the
weak anti-localization and weak localization effects, respectively. This is attributed to
the Berry phase difference between time-reversed trajectories circulating the Fermi
sphere that encloses the monopole charges. From standard Feynman diagram
calculations, we further show that the weak-feld magnetoconductivity at low
temperatures is proportional to −√𝐵 in double-Weyl semimetals and −√𝐵 in singleWeyl semimetals, respectively, which could be verified experimentall
Reference:
[1] X Dai, HZ Lu, SQ Shen, H Yao, arXiv:1512.03339, 2015
[email protected]; [email protected]
313
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Topological phase transition induced extreme magnetoresistance in
TaSb2
Zhen Wang,1,2,* Yupeng Li,1,2,*Yunhao Lu,2 Zhi-Xuan Shen,1 Feng Sheng,1 Chunmu Feng,1
Yi Zheng,1, 3, 4 andZhu-An Xu1, 2, 3, 4
1
Department of Physics, Zhejiang University, Hangzhou 310027, P. R. China
State Key Lab of Silicon Materials, Zhejiang University, Hangzhou 310027, P. R. China
3
Zhejiang California International NanoSystems Institute, Zhejiang University, Hangzhou
310058, P. R. China
4
Collaborative Innovation Centre of Advanced Microstructures, Nanjing 210093, P. R. China
2
Abundant intriguing phenomenon recently discovered in transition metal pnictide
such as extremely large magnetoresistance (XMR), negative magnetoresistance (NMR)
arouse extensive interests in condensed matter physics. Here, we report XMR of 1.72
million percent in new discovered material of single crystal TaSb2 at 1.5 K and 15 T.
A manifestation of nearly perfect compensation between electron and hole pockets
induces the quadratic growth of magnetoresistance dose not saturate up to 15 T. Using
temperature-dependent MR, Hall and thermoelectric coefficients of Nernst and
Seebeck, we confirme two pronounced temperature induced Lifshitz transitions at
around 20 K and 60 K, respectively. Shubnikov-de Haas (SdH) as well as de Haas-van
Alphen (dHvA) effect supported by density-functional theory (DFT) calculations reveal
that along the F − L line in the first brillouin zone, the main hole Fermi pocket of TaSb2
forms a unique flat shoulder structure of which band top is just a few meV above the
Fermi level. As the temperature increasing the shoulder pocket disappears, leading to
the first topological phase transition at 20 K. The second topological phase transition
occurs at around 60K when the temperature pushes the Fermi level totally above the
band top of the main hole pocket. Considering the similar phenomenon also happened
in like WTe2, the Lifshitz transition may play an important role in these materials.
314
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Split Fermi surfaces in chiral cubic ullmannite-type compounds
Hisatomo HARIMA1
1
Department of Physics, Kobe University, Nada Kobe 657-8501, Japan
The electronic structure and the Fermi surfaces are investigated for iso-electronic
compounds NiSbS and PdBiSe, based on an FLAPW band structure calculations. A
mineral ullmannite NiSbS belongs to the tetrahedral class T [1], which is the lowest
symmetry class of the isometric (cubic) system. The space group #198 (P213, T4) is the
same as MnSi, showing non-Fermi liquid behavior [2]. In contrast to the unique
magnetic properties realized in MnSi, most of the ternary ullmannite-type compounds
have been reported as superconducting [3, 4]. It is a non-symmorphic cubic chiral
structure. Totally 4 hole and 4 electron Fermi surfaces are obtained, which are not
degenerated by spin, due to the lack of the space inversion symmetry [5, 6]. The
electronic band structure and the topology of the Fermi surfaces of both compounds are
very similar, but the magnitudes of the splitting of the Fermi surfaces are quite
different.The large spin-splitting in PdBiSe is mainly caused by the strong spin-orbit
interaction of Bi 6p electrons. It turns out that the relativistic mass velocity effect is
important for the spin-orbit interaction [6]. In order to understand the electronic band
structure of NiSbS, the band structure and Fermi surfaces of the centrosymmetric
analogue CoSe2,which belongs to Pyrite-type crystal structure, are also investigated.
Reference:
[1] A. J. Foecker and W. Jeitschko: J. Solid State Chem. 162 (2001) 69.
[2] C. Pfleiderer, S. R. Julian, and G. G. Lonzarich: Nature 414 (2001) 427.
[3] F. Hulliger and J. Müller: Phys. Lett. 5 (1963) 226.
[4] B. Joshi, A. Thamizhavel, and S. Ramakrishnan: J. Physics: Conf. Series 592
(2015) 012069.
[5] M. Kakihana, et al: J. Phys. Soc. Jpn. 84 (2015) 094711.
315
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Dirac Heavy Fermion Semimetal as a parent phase of Topological
Kondo Insulators
X. Y. Feng1 , H. Zhong1, J. Dai1 , and Q. Si2
1
2
Department of Physics and Astronomy, Rice University, Houston, TX 77005, USA
A topological Kondo insulator cannot be driven from a topological insulator just by
tuning a single smooth parameter like the Kondo coupling. To go beyond this no-go
theorem in Kondo systems with distinct Kondo and spin-orbit couplings, we should
look for an intermediate semimetallic Kondo state from which an topological Kondo
insulator can be driven, in the same sense that a topological insulator can be derived
from the Dirac semimetal by the spin-orbit coupling. Here, we show that such a novel
state, dubbed as Dirac heavy fermion semimetal, do exist in a honeycomb Anderson
lattice model in the dilute carrier limit, corresponding to a quarter-filling of conduction
band. Our results point to the dilute carrier limits of the heavy-fermion systems as a
new setting to study strongly correlated insulating and topological states.
Reference:
[1] X.Y. Feng et al., to appear, 2016.
316
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Consitentency of ARPES and dHVA for Surface States of SmB6
J. D. Denlinger1, Sooyoung Jang1,2, G. Li3, Kai Sun3, J. W. Allen3, D.-J. Kim4, Z. Fisk4, Lu Li3
1
2
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
Department of Physics, Pohang University of Science and Technology, Pohang, Korea
3
Department of Physics, University of Michigan, Ann Arbor, MI, USA
4
Department of Physics, University of California, Irvine, CA, USA
The mixed valent compound SmB6 is of high current interest as the first candidate
example of topologically protected surface states in a strongly correlated insulator and
also as a possible host for an exotic bulk many-body state that would manifest
properties of both an insulator and a metal [1]. Two different de Haas van Alphen
(dHvA) experiments [1,2] have each supported one of these possibilities, while angle
resolved photoemission spectroscopy (ARPES) for the (001) surface has supported
the first, but without quantitative agreement to the dHvA results. We present new
ARPES data for the (110) surface and a new analysis of all published dHvA data and
thereby bring ARPES and dHvA into substantial consistency around the basic narrative
of two dimensional surface states [3].
Reference:
[1] B. S. Tan et al., Science 349, 6245 (2015)
[2] G. Li et al., Science 346, 1208 (2014)
[3] J. D. Denlinger et al., arXiv:1601.07408 (2016)
317
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Ce3p hard x-ray photoelectron spectroscopy study of CeRu4Sn6
M. Sundermann1, K. Chen1, Y. Utsumi2, K.-D. Tsuei3, J. Haenel4, A. Prokofiev4, A. Tanaka5,
S. Paschen4, L.H. Tjeng2, A. Severing1
1
Institute of Physics II, University of Cologne, Cologne, Germany
3
National Synchrotron Radiation Research Center, Hsinchu, Taiwan
4
Institute of Solid State Physics, Vienna University of Technology, Vienna, Austria
5
Department of Quantum Matter, ADSM Hiroshima University, Higashi-Hiroshima, Japan
2
We had inferred from spectroscopy results combined with band structure
calculations that CeRu4Sn6 fulfills the requirements for a strongly correlated material
with nontrivial topology [1]. CeRu4Sn6 is a tetragonal Kondo insulator [2] where the
hybridization of f and conduction electrons leads to the opening of a gap. Accordingly,
the resistivity rises as temperature decreases, however below T ≈ 10K, the resistivity
appears to be finite. Speculations about conducting surface states were hardened by the
spectroscopic confirmation that the lowest Kramers doublet has the Γ6 symmetry (Jz =
½) and the finding of a large Kondo temperature (TK ≈ 170K) which was deduced from
the temperature dependence of the f-shell occupation.
Here we present Ce3p core level hard x-ray photoelectron spectroscopy (HAXPES)
data of CeRu4Sn6 and a quantitative analysis of the f-shell occupation. The HAXPES
data were taken at the Taiwan beamline BL12XU at SPring-8. The cage-like crystal
structure of CeRu4Sn6 gives rise to strong plasmon excitations which coincide in
energy with the intensities due to the 𝑓 𝜃 contribution in the ground state. We can
correct for these plasmon intensities by combining a configuration interaction model
based on a single non-dispersive valence band [3] with a full multiplet simulation [4]
and obtain reliable values of the f-shell occupation. For rare earth atoms, the 3d
emission is more commonly used for this purpose; however, here the Sn3s emission is
in the same energy window, thus preventing a quantitative analysis. We therefore use
the Ce3p core level. A good fit to the data is obtained with a 𝑓 𝜃 contribution of ≈7%.
This value is larger than in the previous L3 PFY-XAS study since here final state effects
have been accounted for. We can further give a value for the effective hybridization
Veff and compare it to values of HAXPES data of other cerium compounds which were
analyzed in the same manner [5].
Reference:
[1] M. Sundermann et al., Scientific Reports 5, 17937 (2015)
[2] I. Das, PRB 46, 4250 (1992) & A. Strydom et al., Physica B 359-361, 293
(2005) & S. Paschen et al., J. Phys. Conf. Ser. 200, 012156 (2010) & E.M. Brüning
et al., PRB 82, 125115 (2010)
[3] J.-M. Imer, E. Wuilloud, Zeitsch. Phys. B: Condens. Matter 66, 153–160 (1987)
[4] F. Strigari et al., J.Elec.Spec.Rel.Phen. 199, 56-63 (2015)
[5] M. Sundermann et al., arXiv Cond-Mat arXiv1601.03270 (2016)
318
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Topological insulating state in ZrSnTe crystal
Shancai Wang1, 2, Rui Lou1, 2, Junzhang Ma3, Qiunan Xu3, Hechang Lei1, 2, Hongming
Weng3, 4, Tian Qian3, Hong Ding3, 4
1
Department of Physics, Renmin University of China, Beijing 100872, China
Beijing Key Laboratory of Opto-electronic Functional Materials & Micro-nano
Devices, Renmin University of China, Beijing, China
3
4
2
Topological insulators (TIs) possess topologically protected helical edge states, for
which backscattering is prohibited by time-reversal symmetry, leading to
dissipationless transport edge channels and to the quantum spin Hall effect (QSHE).
The proved two-dimensional (2D) TIs are the quantum-wells of HgTe/CdTe and
InAs/GaSb, which show QSHE only at ultra-low temperatures. This seriously obstructs
further experimental studies and potential applications. Here we reported the angleresolved photoemission spectroscopy (ARPES) study on the ZrSnTe crystals. By
detailed comprising the ARPES results with first-principles calculations, we argue that
this material could be a candidate of 2D TI.
319
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Shubnikov-de Haas oscillations in BiTeI under high pressure
HongEn Tan1, Phil Brown1, Hui Chang1, Xiaoye Chen1, Geetha Balakrishnan2, John R. Cooper1,
F.Malte Grosche1
1
University of Cambridge, Cavendish Laboratory, Cambridge, UK
2
University of Warwick, Dept. of Physics, Coventry, UK
BiTeI is a non-centrosymmetric polar semiconductor that possesses a strong intrinsic
Rashba-type spin-orbit interaction that leads to a chiral spin texture of the conduction
and valence band. It is predicted that as hydrostatic pressure is applied, the energy gap
of BiTeI would decrease and ultimately band inversion would occur, potentially giving
rise to a pressure-induced topological insulator [1]. Samples of self-doped BiTeI with
varying doping levels were mounted in a piston cylinder cell and we used Shubnikov
de-Haas oscillations to track the evolution of the band structure up to a pressure of 24
kbar. We have tracked two frequencies with applied pressure, corresponding to the
outer and inner Fermi surface orbits, and we analyse our results by fitting these
frequencies to the results expected from a Rashba Hamiltonian.
Reference:
[1] M. S. Bahramy et al., Nature Comm. 3, 679 (2012).
E-mail for corresponding author: [email protected]
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Helicity preserving photoluminescence from Bi2Se3
G. Blumberg1,H.H. Kung1
An ecxciton – in-band-gap bound state of an electron and hole – is one of the
fundamental excitations in insulators. Conventionally, the exciton emission is
unpolarized due to rapid phase and energy relaxation of the photo-excited electron-hole
pairs during formation of an excitonic bound state. In a few rare examples partially
polarized exciton emission has been demonstrated by engineering structures in which
electron band and/or spin degeneracies are lifted.
In this work we report a surprising discovery of polarization preserving
photoluminescence (PL) from Bi2Se3 topological insulator (TI). High degree of PL
polarization is consistently demonstrated in both bulk and thin film samples at low and
even at room temperature. To explain the polarization preserving PL we propose that
the emission occurs from a photo excited bound state of a topologically protected
relativistic gapless surface band hole orbiting a massive bulk band electron. Two
degenerate such relativistic excitons carrying opposite orbital momenta can be
constructed. Depending on the helicity of the photo-excitation, one of these two bound
states is selectively excited. The interchange between the two states is topologically
protected, hence, the reported inhere temperature independent highdegree of emission
polarization.
This discovery of helicity preserving PL offers novel fast characterization tool for
detecting the topological surface states, which is essential for developing optoelectronic
and spintronic devices making use of TIs. As such, the discovery is fundamental both
for understanding the matter of the TIs, the study of relativistic quantum effects, and
for the applications using topological protection.
We acknowledge collaboration with M. Salehi, X. Wang, N. Koirala, M. Brahlek, A.
Lee, S.-W. Cheong, S. Oh, and L. Levitov. Research at Rutgers was supported by the
National Science Foundation under Awards NSF DMR-1104884 and NSF DMR1405303.
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Spin-valley physics induced by charge order on a triangular lattice
Y. Sugita and Y. Motome
Department of Applied Physics, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo
The spin-orbit coupling (SOC) has attracted much attention in condensed matter
physics since the SOC causes fascinating phenomena, such as the spin Hall effect and
multiferroics. The SOC is generally given by
𝐻𝑠𝑜𝑐 ~(𝑝 × 𝛻𝑉(𝑟)) ∙ 𝑠 ,
(1)
where p is the momentum operator, s is the spin momentum operator, and V(r) is the
crystalline electric potential in which electrons move. Thus, the SOC takes different
form depending on V(r). For instance, in the systems without spatial inversion
symmetry, V(r) acquires a uniform odd-parity component, which leads to the so-called
antisymmetric SOC (ASOC). Such ASOC has been intensively discussed as the origin
of unconventional superconductivities and magnetoelectric effects. On the other hand,
in the centrosymmetric systems where the inversion centers are not at lattice sites, e.g.,
a zigzag chain and honeycomb lattice, there exists a hidden ASOC in a sublattice
dependent form. In this case, a spontaneous parity breaking by electronic ordering can
activate the hidden ASOC and induce spin splitting in the band structure and
magnetoelectric effects [1-3]. This suggests a new way of controlling the SOC through
the electronic degrees of freedom.
In order to explore such emergent SOC physics by spontaneous symmetry breaking,
we investigate an extended two-orbital Hubbard model on a triangular lattice with SOC.
In particular, we focus on spontaneous charge ordering. Using the Hartree-Fock
approximation, we obtain the ground-state phase diagram that contains charge ordered
phases, where the charge disproportionation forms a honeycomb or kagome network.
We find that these charge ordered phases can be topological insulators due to the SOC.
In addition, we clarify that, when introducing the lattice distortion, the system shows
spin splitting, in a similar way observed in transition metal dichalcogenides [4]. In this
presentation, we show the electronic states and transport phenomena of the charge
ordered insulators and discuss the application of our results to charge density wave
states in transition metal dichalcogenides.
References:
[1]Y. Yanase, J. Phys. Soc. Jpn. 83, 014703 (2014).
[2]S. Hayami, H. Kusunose, and Y. Motome, Phys. Rev. B 90, 024432 (2014).
[3]S. Hayami, H. Kusunose, and Y. Motome, Phys. Rev. B 90, 081115(R) (2014).
[4]X. Xu, W. Yao, D. Xiao, and T. F. Heinz, Nat. Phys. 10, 343 (2014).
322
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Topological photonic crystal with equifrequency Weyl points
Luyang Wang1, Shao-Kai Jian1, Hong Yao1,2
1
2
Institute for Advanced Study, Tsinghua University, Beijing, China
Weyl points in three-dimensional photonic crystals behave as monopoles of Berry
flux in momentum space. Here, based on general symmetry analysis, we show that a
minimal number of four symmetry-related (consequently equifrequency) Weyl points
can be realized in time reversal invariant photonic crystals. We further propose a new
and experimentally-feasible way to modify double-gyroid photonic crystals to realize
four equifrequency Weyl points, which is explicitly confirmed by our first-principle
photonic band-structure calculations. Remarkably, photonic crystals with
equifrequency Weyl points are qualitatively advantageous in applications including
angular selectivity, frequency selectivity, invisibility cloaking, and the 3D-imaging.
Reference:
[1] Luyang Wang, Shao-Kai Jian and Hong Yao, Arxiv 1511.09282 (2015)
323
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Optical spectroscopy and pump-probe studies on charge density
wave orders in LaAgSb2
R. Y. Chen1, S. J. Zhang1, M. Y. Zhang1 and N. L. Wang1,2
1
100871, China
2
Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
The layered lanthanum silver antimonide LaAgSb2 exhibits many interesting
physical properties. The compound was known to experience two charge density wave
(CDW) phase transitions at 207 and 186 K, respectively. Recent transport measurement
revealed a large linear magnetoresistance, suggesting possible contribution from Dirac
fermions. Presence of linear Sb 5p band dispersion and the Dirac-cone-like structure
was indeed observed by ARPES experiment. We present optical spectroscopy and
pump-probe measurement on the compound. We observe clearly energy gap formation
below the CDW phase transition temperatures in optical conductivity, which removes
most part of the free carrier spectral weight. The time resolved pump-probe
measurement indicates that the photoinduced reflectivity can be well described by a
single exponential decay for the whole measurement temperature range, except for the
emergence of strong oscillations upon entering the CDW states. The oscillations come
from the amplitude mode of CDW collective excitations. We find that the frequencies
of the two amplitude modes are surprisingly low: only 0.12 THz for the CDW order
with higher transition temperature and 0.34 THz for the lower one. The low energy
scale of the CDW amplitude mode implies that the acoustic phonon mode, which
experiences a softening to zero frequency and triggers the CDW transition, also has
very low energy scale. We elaborate that those unusual properties are closely linked to
the extremely small nesting wave vectors of the two CDW orders.
324
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Thermal Hall conductivity of spin-triplet superconductor with time
reversal symmetry breaking
Y. Imai1, K. Wakabayashi2, M. Sigrist3
1
Department of Physics, Saitama University, Saitama, Japan
2
Kwansei-Gakuin University, Hyogo, Japan
3
Theoretische Physik, ETH-Hönggerberg, Zürich, Switzerland
Motivated by the superconductor Sr2RuO4 the thermal Hall conductivity is
investigated in a spin-triplet superconducting phase with time-reversal symmetry
breaking. In bulk Sr2RuO4 the topological properties originate from the band whose
Fermi level lies close to a Lifshitz transition tunable by lattice distortion, chemical
doping and pressure effects. Although the Chern number switches at the Lifshitz
transition, there is only a minor effect on the edge current. Using a tight-binding model
corresponding to the multiband of Sr2RuO4 we calculate various physical quantities
within a Bogoliubov-de Gennes approach. We study particularly the low-temperature
properties of thermal Hall conductivity and demonstrate that it consists of a
temperature-linear term and exponential term, which are directly associated with the
Chern number and the amplitude of the gap function. Thus, the thermal Hall conductive
switches with the change of the Chern number at the Lifshitz transition. With this we
demonstrate that the thermal Hall effect is directly connected with the topological
properties, in contrast to the charge edge currents.
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Topological Superconductivity with Magnetically-induced
Excitation Gap and Asymmetric Majorana Edge States
Akito Daido1 and Youichi Yanase1
1
Department of Physics, Kyoto University
Topological superconductors (TSCs) attracts great attention, and much effort has
been devoted to searches of candidate materials. Recently numerical study proposed a
new scenario of realizing gapful topological superconductors (TSCs) [1]: 2D d(+p)wave SCs, which are originally gapless, become gapful under magnetic field and are
characterized by topological invariants in the so-called periodic table of topological
phases [2]. 2D d-wave SCs are experimentally realized in various strongly correlated
electron systems ([3, 4], for example); Therefore, this scenario leads to a major
breakthrough in the design of TSCs, broadening the field of searching them.
We discuss a generalization of this scenario by deriving analytic expressions of
excitation spectrum. The mechanism of gap generation is generalized into all the paritymixed nodal SCs without orbital degrees of freedom. Among them, 1D and 2D SCs
may become topologically nontrivial, because they are classified into the symmetry
class D. Magnetically-induced excitation gap is roughly estimated to be of the order of
0.1~1 K in cuprates. It may be observable in experiment. Thus, 2D cuprate SCs under
magnetic field are a strong candidate of gapful TSCs.
We also show novel Majorana edge states in such systems when the quasiparticle
excitation is gapless under a tilted magnetic field (Fig.2). Properties of the edge states
are quite different between an edge and the edge on the opposite side. Such unusual
edge states are realized because of the combination of time-reversal-symmetry
breaking and inversion-symmetry breaking.
Reference:
[1]
[2]
[3]
[4]
T. Yoshida and Y. Yanase, to appear in PRB.
A. P. Schnyder et al., PRB 79, 060505 (2008)
A. T. Bollinger et al., Nature 472, 458 (2011)
M. Izaki et al., APL 91, 122507 (2007)
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Effects of single ion anisotropy and bond alternation in the
S=2 Heisenberg model
S. Miyakoshi1, S. Nishimoto2,3, Y. Ohta1
1
Department of Physics, Chiba University, Chiba, Japan
2
IFW Dresden, Dresden, Germany
3
TU Dresden, Dresden, Germany
Symmetry protected topological (SPT) phases are a gapped phase under a given
symmetry. Unless any symmetries that protect the SPT phases are broken, the SPT
phases can be distinguished from each other. Recently, it was pointed out that the
entanglement spectrum of the many-body state characterizes such SPT phases. In
particular, the degeneracy of the entanglement spectrum reflects the corresponding
symmetries and edge states of the system.
Motivated by recent studies of the SPT phases, we investigate the bond-alternating
Heisenberg model with general integer spins and clarify the entanglement properties of
the ground state using the density matrix renormalization group method. In particular,
this model has the intermediate phase at S>1 due to the bond alternation [1,2]. The
entanglement properties of this phase in the case of S>2 have not been studied
sufficiently because of the numerical difficulties under an extremely small spin-gap
situation. We studied the case of S=1,2,3 using the antiperiodic boundary condition.
Under the antiperiodic boundary condition, we found that the doubly degenerate spectra
which characterize the intermediate phase can be observed in the entanglement
spectrum. We will discuss the effects of the single-ion uniaxial anisotropy and bond
alternation.
Reference:
[1] I. Affleck and F. D. M. Haldane, Phys. Rev. B 36 5921 (1987).
[2] M. Oshikawa, M. Yamanaka and I. Affleck, Phys. Rev. Lett. 78, 1984 (1997).
327
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Fractional Electric Charge and Massive Quasiparticles on the
Domain Wall between Topological Insulators and Spin Ice
Compounds
E. Imai1, T. Sasaki1, I. Kanazawa1
1
Department of Physics, Tokyo Gakugei University, Tokyo, Japan
Time reversal-invariant topological insulators have been classified in (3+1)dimension.
In addition, the prominent examples of emergent quasiparticles are magnetic
monopoles emerge in a class of exotic magnets known collectively as spin ices.
Recently one (I,K) of us has proposed exotic quasiparticles with fractional charges in
semiconductor-dot from collectively induced-charge effects on a domain wall shell[1].
In this study, we will discuss the anomalous properties of quasiparticles on the
domain wall between spin ice compounds and topological insulators
Reference:
[1] I. Kanazawa, J. Phys. Cont. Set. 400, 042028 (2012)
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Induced Topological-charges on a Domain Wall of the Semiconduc
tor Dot and the D-brane-like Dot
I. Kanazawa1
1 Department of Physics, Tokyo Gakugei University, Tokyo, Japan
Self-assembled quantum dots (SAQD) have been intensively investigated because of
their potential applications in many optoelectronic devices as well as from a
fundamental physics point of view.
The present author [1] has reported the importance of the hole-induced domain-wall
in magnet resistance in diluted magnetic semiconductors.
In this study, we discuss an anomalous excitations with fractional charges on a
domain wall of a narrow-gap semiconductor-dot from viewpoint of field-theoretical
formula.
Reference:
[1] I. Kanazawa, Phys. Lett. A355, 460 (2006)
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Quantum Oscillations, Thermoelectric Coefficients, and the Fermi
Surface of Semimetallic WTe2
Zengwei Zhu,1,* Xiao Lin,2 Juan Liu,1 Benoî
t Fauqué,2 Qian Tao,2 Chongli Yang,3 Youguo
Shi,3 and Kamran Behnia2
1
2
LPEM (CNRS-UPMC), ESPCI, 75005 Paris, France
3
Institute of Physics and Beijing National Laboratory for Condensed Matter Physics,
We present a study of angle-resolved quantum oscillations of electric and
thermoelectric transport coefficients in semimetallic WTe2, which has the particularity
of displaying a large B2 magnetoresistance. The Fermi surface consists of two pairs of
electronlike and holelike pockets of equal volumes in a “Russian doll” structure. The
carrier density, Fermi energy, mobility, and the mean-free path of the system are
quantified. An additional frequency is observed above a threshold field and attributed
to the magnetic breakdown across two orbits. In contrast to all other dilute metals, the
Nernst signal remains linear in the magnetic field even in thehigh-field (ωcτ≫ 1)
regime. Surprisingly, none of the pockets extend across thec axis of the first Brillouin
zone, making the system a three-dimensional metal with moderate anisotropy in Fermi
velocity, yet a large anisotropy in the mean-free path.
Reference:
*[email protected]
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Edge-Tunneling Behaviour of Anisotropic Quantum Hall States
Ruizhi Qiu
Institute of Materials, China Academy of Engineering Physics
Topological order of quantum Hall states manifest itself not only in the ground state
degeneracy but also in the edge structure [1, 2]. For Abelian quantum Hall states, the
gapless edge excitation can be described in the chiral Luttinger liquid theory [1]. The
chiral Luttinger liquid theory predicted an amazing non-Ohmic tunneling I -V relation
I~Vα for tunneling. Therefore, the edge-tunneling experiment and the theoretical
calculation of edge-tunneling exponent α was regarded as a useful way of measuring
the topological order. In particular, Wan et al [3] calculated the edge Green's function
of fractional quantum Hall liquids with isotropic electron-electron interaction and
confinement via exact numerical diagonalization and showed the tunneling
characteristic are perfectly consistent with the chiral Luttinger theory.
However, the realistic quantum Hall system may be anisotropic, which can be
naturally understood for the anisotropic band mass or dielectric tensor [4-7]. In
addition, the quantum Hall system in fast-rotating Fermi gases with anisotropic dipolar
interaction is also attractive [8]. Apparently, the edge-tunnelling behaviour should be
carefully investigated in these anisotropic system. Our calculation shows that the edgetunnelling exponent α of anisotropic system drastically deviates that of isotropic
system, which may reveal different topological order in this system.
Reference:
[1] X.-G. Wen, International Journal of Modern Physics B, 1991, 5, 1641.
[2] X.-G. Wen, Advances in Physics, 1995, 44, 405{473.
[3] X. Wan, F. Evers and E. H. Rezayi, Phys. Rev. Lett., 2005, 94, 166804.
[4] F. D. M. Haldane, Phys. Rev. Lett., 2011, 107, 116801.
[5] R.-Z. Qiu, F. D. M. Haldane, X. Wan, K. Yang and S. Yi, Phys. Rev. B, 2012, 85, 115308.
[6] B. Yang, Z. Papic, E. H. Rezayi, R. N. Bhatt and F. D. M. Haldane, Phys. Rev. B, 2012, 85,
165318.
[7] H. Wang, R. Narayanan, X. Wan and F. Zhang, Phys. Rev. B, 2012, 86, 035122.
[8] R.-Z. Qiu, S.-P. Kou, Z.-X. Hu, X. Wan and S. Yi, Phys. Rev. A, 2011, 83, 063633
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Single Crystal NMR Studies of PrT2Al20 Systems (T = Nb, Ta)
T. Kubo1, R. Miyake1, H. Kotegawa1, H. Tou1, H. Harima1, R. Higashinaka2, A.
Nakama2, Y. Aoki2, H. Sato2, Y. Ihara3, T. Goto4, T. Sasaki5
1
2
Department of Physics, Graduate School of Science, Kobe University, Kobe, Japan
Department of Physics, Graduate School of Science and Engineering, Tokyo Metropolitan
University, Hachioji, Japan
3
Department of Physics, Faculty of Science, Hokkaido University, Sapporo, Japan
4
Faculty of Science and Technology, Sophia University, Chiyoda, Japan
5
PrT2Al20 systems (T = transition metal) exhibit quadrupole ordering,
superconductivity, and non-Fermi liquid (NFL) behaviors at low temperatures. The
relationship between the origin of these phenomena and the multipole degrees of
freedom of 4f electrons has been extensively studied [1–3]. Among them, PrNb2Al20
shows NFL behaviors below 2 K and shows no phase transition above 75 mK [4,5],
while PrTa2Al20 exhibits multipole ordering at TO = 0.7 K and shows Fermi liquid
behaviors below TO [6].
In this study, we measured the temperature, and field dependences of the spin-lattice
relaxation rate 1/T1 at various atomic sites by using single crystal PrT2Al20 (T = Nb, Ta).
93
Nb-1/T1 in PrNb2Al20 shows 1/T1 ~ T2/3 behavior, which deviates from Fermiliquid
behavior of 1/T1T = const. 27Al-1/T1 in PrTa2Al20 shows the sudden decrease at TOup to
19 T, while27Al-1/T1 in PrNb2Al20 shows no anomaly above 1.6 K. These contrasting
results suggest the relationship between the low energy excitations and the ground state
of PrT2Al20 systems.
Reference:
[1] A. Sakai and S. Nakatsuji, J. Phys Soc. Jpn. 80, 063701 (2011).
[2] A. Sakai et al., J. Phys. Soc. Jpn. 81, 083702 (2012).
[3] M. Tsujimoto et al., Phys. Rev. Lett. 113, 267001 (2014).
[4] R. Higashinaka et al., 80, SA048 (2011).
[5] T. Kubo et al., J. Phys. Soc. Jpn. 84, 074701 (2015).
[6] R. Higashinaka et al., unpublished.
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Theoretical Study for Non-Fermi Liquid Behaviors and Ordered
States in Pr 1-2-20 Compounds
Atsushi Tsuruta1, Kazumasa Miyake2
1
Department of Materials Engineering Science, Osaka University, Toyonaka, Osaka 560-8531,
Japan
2
Toyota Physical and Chemical Research Institute, Nagakute, Aichi 480-1192, Japan
Non-Fermi liquid behaviors in the resistivity have been reported in PrV2Al20 [1] and
PrIr2Zn20 [2]. Namely, the electrical resistivity is in proportion to T 0.5 in rather wide
low T region above the quadrupolar transition temperature TQ . The Specific heat
increases like C0− C1T 0.5 as T decreases at T >TQ . The ground state of the crystallineelectric field (CEF) of the local f-electron was identified to be the Γ3 non-Kramers
doublet in 4f2 configuration [2]. Such a system in f2 configuration is expected to exhibit
an anomalous behaviors associated with the two-channel Kondo effect.
Tsuruta et al. investigated electronic states in the M-channel Anderson lattice model
using the expansion from the limit of large spin-orbital degeneracy N( 1/N - expansion)
[3], and showed that the inclusion of the self-energy of O((1/N)0) leads to heavy
electrons with degeneracy of channel and spin-orbit. In the single channel case, the
imaginary part of the self-energy of conduction electrons (ISE) exhibits the Fermi liquid
behavior: i.e. ISE is given by a form proportional toT 2 owing to the inter-site correlation
effects in higher order terms in power of 1/N.
In the two-channel case, however, a T-linear term in ISE at the Fermi level, in
contrast to aT 2-term in the Fermi liquid is found in the limit of T → 0. However, a T 0.5
dependence appears in a rather wide low T region, which explains quite well the nonFermi liquid behavior observed experimentally.
Because of the anomalous T dependence of ISE, the chemical potential is given by
μ0 − μ1T 0.5, and the specific heat is given by C0 − C1T 0.5. We also obtain the
scalingbehavior f (T/T0) ,T0 is defined as thecrossover temperature at which the T
dependence of ISE starts to deviate from the √T dependence to that with a much lower
exponent as Tincreases, in electrical resistivity, chemical potential, specific heat and
magnetic susceptibility, explaining non-Fermi liquid properties observed inPr1-2-20
compounds.[4]
We can also explain the difference in the T dependence of PrV2Al20 and PrTi2Al20 as
the difference of the cf hybridization. We can also explain the crossover from Fermi
liquid to non-Fermi liquid observed in PrTi2Al20 under pressure, and salient increases
of the superconducting transition temperatures TSC of PrT2Al20 (T=Ti,V) and PrT2Zn20
(T=Ir, Rh) towards the critical pressure where the quadrupolar order vanishes, i.e., TQ→
0.
Reference:
[1] A. Sakai and Nakatsuji, J. Phys. Soc. Jpn. 80, 063701 (2011).
[2] T. Onimaru et. al., Phys. Rev. Lett. 106, 177001 (2011).
[3] A. Tsuruta et. al., J. Phys. Soc. Jpn. 68, 1067 (1999).
[4] A. Tsuruta and K. Miyake, J. Phys. Soc. Jpn. 84, 114714 (2015).
333
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Crystal Growth and Anisotropic Magnetic Properties of PrAu4Si2
Arvind Yogi, R. Kulkarni, S. K. Dhar and A. Thamizhavel
Department of Condensed Matter Physics and Materials Science, Tata Institute of
Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai 400 005, India
Single crystals of PrAu4Si2 have been grown by high temperature solution growth
with Au-Si eutectic composition as self-flux. Large size platelet like single crystals
were obtained which were easy to cleave. The Laue diffraction pattern on the as grown
single crystal revealed that the flat plane of the crystal corresponds to (001) plane. From
the powder x-ray diffraction we confirmed that this compound crystallizes in the
tetragonal crystal structure with the space group P-4m2 and lattice constants a = 4.333
Å and c = 27.501 Å. The lattice parameters are close to that of the isostructural
CeAu4Si2 [1]. There are three Pr sites in the crystal structure. A large anisotropy was
observed in the magnetic susceptibility and magnetization data. A sudden rise in the
magnetic susceptibility was observed at 2.7 K indicating the magnetic ordering at this
temperature. The magnetization measurement performed at 2 K revealed a sharp rise in
the magnetization at low fields and exhibit a quasi-linear increase at higher fields. The
magnetization value obtained at a field strength of 7 T was only 1.88 µB/Pr which is
much smaller compared to the saturation value of a trivalent Pr atom. The easy axis of
magnetization was found to be the [001] axis. The bulk magnetic ordering at 2.7 K is
confirmed by the heat capacity measurement.
Reference:
[1] H. Nakashima, A. Thamizhavel et al., J. Alloys and Comp. 424 (2006) 7.
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Evidence of Fermi surface reconstruction in the thermoelectricsignal
of URhGe near reentrant superconductivity
A. Gourgout1,2, A. Pourret1,2, D. Aoki 1,2,3 and J. Flouquet1,2
1
Univ. Grenoble Alpes, INAC/SPSMS, Grenoble, France
2
CEA INAC/SPSMS, Grenoble, France
3
Institute for Material Research, Tohoku University, Oarai, Japan
The last decades have seen a renovated interest in the topic of quantum phase
transitions (QPTs), which have had a surprising impact in explaining several exotic
low-temperature properties of a variety of innovative materials which do not fit
conventional many-body theories. Recent experimental and theoretical analysis of
ferromagnetic (FM) QPTs have shown that the second order phase transition turns into
a first-order one when approaching the absolute zero temperature. Thus, the emerging
scenario indicates the presence of a tri-critical point (TCP) in proximity of a QPT. In
this context, we choose to study the tri-critical fluctuations in the FM superconductor
URhGe[1]. URhGe is a singular case as in this Isingorthorombicferromagnet, with FM
moments oriented along its easy c axis, a transverse magnetic field applied along the
hard axis b induces at low temperature a field-reentrant superconducting phase (RSC)
on a narrow field window around HR = 12.5 T, where the magnetic moments are
reoriented from c axis to b axis.
We have realized systematic thermoelectric power (TEP) and resistivity experiments
on URhGe with different orientations of thermal gradient and electrical currents with
respect to magnetic field in order to investigate electronic properties near HR. The
validity of the Fermi liquid T2 law through HR demonstrates clearly that no quantum
critical point occurs at HR, thus the FM transition line at HR becomes first order
implying the existence of a TCP at finite temperature [2]. Observation of new energies
scales converging to the TCP imply the existence of longitudinal magnetic fluctuations
that strongly increase in the vicinity of the TCP stimulating reentrance of the
superconducting. The abrupt change of sign observed in the thermoelectric power
clearly suggests a strong change of the Fermi surface at HR.
Reference:
[1] D. Aoki, et al., Nature 413, 613 (2001) [2] E.Yelland, et al., Nature Physics 7, 890 (2011) 335
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Ferromagnetic criticality and Fermi surface evolution undermagnetic
field and high pressure studied in UCoGe
Gaël Bastien1,2, Adrien Gourgout1,2, Daniel Braithwaite1,2, Dai Aoki1,2,3, Shingo Araki4,
Alexandre Pourret1,2, Ilya Sheikin5, Gabriel Seyfarth5 , Jean-Pascal Brison1,2, Georg Knebel1,2,
Jacques Flouquet1,2
1Univ. Grenoble Alpes, INAC-PHELIQS, F-38000 Grenoble, France
2INAC/PHELIQS, CEA-Grenoble, 17 rue des martyrs, 38054 Grenoble, France
3IMR-Tohoku University, Oarai, Japan
4Department of Physics, Okayama University, Okayama 700-8530, Japan
5LNCMI-G, CNRS, 25 Rue des Martyrs, 38042 Grenoble, France
Ferromagnetic quantum criticality and unconventional superconductivity have
attracted intense interest in recent years. In this presentation we will discuss the
ferromagnetic quantum phase transition and Fermi surface properties as function of
magnetic field and high pressure in the ferromagnetic superconductor UCoGe as
function of high pressure. The magnetic phase diagram has been studied in diamond
anvil cell for pressures up to 10.5 GPa. Ferromagnetism is suppressed at a critical
pressure pc≈ 1 GPa [1,2]. Unconventional superconductivity has been observed over a
large pressure range up to 4GPa. The normal state properties above the superconducting
transition shows strong deviations from the Fermi liquid behavior. Remarkably, at pc
the resistivity is linear in temperature. The temperature and pressure dependence of the
upper critical field for field along the easy magnetization axis can be explained from
the strong influence of magnetic field on the pairing interaction. Magnetic quantum
oscillations were detected both in resistivity and Seebeck effect. Shubnikov-de Haas
oscillations were also measured under pressure up to 2.5GPa. Ambient pressure
measurement for field up to 34T showed several Fermi surface instabilities and Fermi
surface reconstructions at H=16T and H=21T. However, the evolution of Fermi surface
with pressure is small and no distinct change of the quantum oscillations could be
revealed at the critical pressure pc.
Reference:
[1] E. Hassinger, D. Aoki, G. Knebel, J. Flouquet, J. Phys. Soc. Jpn. 77, 073703
(2008)
[2] N. T. Huy, D. E. de Nijs, Y. K. Huang, and A. de Visser, Phys. Rev. Lett. 100,
077002 (2008)
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Coherence Effects of Caroli-de Gennes-Matricon Modesin a Nodal
Topological Superconductor UPt3
Yasumasa Tsutsumi1, Yusuke Kato1
1
Department of Basic Science, The University of Tokyo, Tokyo, Japan
Coherence effects by impurity scattering of Caroli-de Gennes-Matricon (CdGM)
modes in a vortex for nodal topological superconductors have been studied, where we
have focused on candidates for the superconducting state of UPt3 [1] as an example.
The impurity effects are dominated by the coherence factor depending on the wave
function of the CdGM modes. For the zero energy CdGM modes, the coherence factor
vanishes in certain momentum range, which is guaranteed by a topological number
defined on particular momentum space avoiding the superconducting gap nodes. The
characteristic coherence effects can be observed by flux flow conductivity
measurements, inelastic neutron scattering experiments, and quasiparticle interference
imagings.
Reference:
[1] K. Izawa et al., J. Phys. Soc. Jpn. 83, 061013 (2014)
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9
Be-NMR studies on anomalous superconducting phase diagram in
UBe13
Haruki Mtsuno1, Kyohei Morita1, Hisashi Kotegawa1, Hideki Tou1,Yoshinori Haga2, Etsuji
Yamamoto2, Yoshichika Onuki3
1
2
Department of Physics, Kobe University, Kobe, Hyogo 675-8501, Japan
Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195,
Japan
3
Faculty of Science, University of Ryukyus, Nishihara, Okinawa 903-0213, Japan
Heavy fermion superconductor UBe13 shows the superconducting (SC) transition at
Tc = 0.86 K. In the SC state, anomalous behaviors have been observed in
thermodynamics measurements at Ta (<Tc) [1,2]. It has been discussed that the T-H
SC phase diagram of UBe13 has multiple SC phases. The origin of above the anomaly
has been discussed past several decade and suggested a few possibilities, e.g. the
change of the multiple SC order parameters like UPt3, the multiband effect, short range
ferromagnetic order etc [2,3]. In order to clarify unusual property in SC state, we have
carried out 9Be-NMR measurements for a single crystal UBe13 down to 0.1 K at
various magnetic fields. The 9Be Knight shift for Be(II) site stays constant in the
temperature range between Tc>T>Ta, whereas the shift suddenly shows a fractional
reduction below Ta (<Tc) . On the other hand, the 9Be Knight shift for Be(I) site does
not change at all even below Ta.
Reference:
[1] F. Kromer et al., Phys. Rev. Lett., 81, 4476 (1998).
[2] Y. Shimizu et al., Phys. Rev. Lett., 109, 217001 (2012).
[3] M. Sigrist and T. M. Rice, Phys. Rev. B, 39, 2200 (1989).
338
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Origin of sample dependence of magnetism andsuperconductivity
in UNi2 Al3
Shouta Kunikata1, Takeshi Yamaguchi1, Keiichiro Imura1, Kazuhiko Deguchi1, Noriaki
K. Sato1, Tomoo Yamamura2
1
2
Graduate School of Science, Nagoya University, Nagoya, Japan
Magnetism and superconductivity (SC) had been considered to be antagonistic to
each other. Since the discovery of heavy fermion superconductors and high-Tc
superconductors, the correlation of these phenomena has been actively discussed.
From a variety of experimental results, it turned out that, for example, the magnetic
excitons (the collective motion like spin waves in a magnet) mediate the spin-singlet
pairing interaction in UPd2 Al3 [1]. This means that the magnetism can induce
superconductivity. UNi2Al3 is also thought to be an exotic superconductor [2], which
exhibits the coexistence of spin density wave (SDW) (TN ≅ 4.5 K) [3] with SC (TC≅
1 K) at ambient pressure. Interestingly, the spin triplet SC seems to be realized in this
material [4, 5]. While these two compounds have the same crystal structure
(hexagonal PrPd2 Al3 type), they possess the different SC pairing state. Therefore, it
is expected to get information about the correlation of magnetism and SC by
comparing these two heavy fermion compounds. However, this expectation is
obstructed by the difficulty in preparing good-quality single crystal of UPd2 Al3 : In
some samples, both the SDW and the SC vanish. The purpose of the present
investigation is then to reveal a possible origin of the sample dependence of the
magnetism and the SC.
We carried out measurements of x-ray diffraction (XRD), inductively coupled
plasma (ICP) and scanning electron microscope (SEM) analysis on the two type of
single crystalline samples. One shows clear anomalies in the specific heat at TN and
TC, and the other shows no anomalies there. Finally we found that the Ni concentration
plays an important role in the appearance of the specific heat anomalies. These
detailed results will be presented together with the correlation between the magnetism
and the SC.
Reference:
[1] N. K. Sato et al., Nature , 410, 340 (2001).
[2] C. Geibel et al., Z. Phys. B - Condensed Matter, 83, 305 (1991).
[3] A. Hiess et al., Phys. Rev. B, 64, 134413 (2001).
[4] N. Sato et al., J. Phys. Soc. Jpn., 65, 1555 (1996).
[5] K. Ishida et al., Phys. Rev. Lett., 89, 037002(2002).
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Upper critical field in the ferromagnetic superconductor UCoGe
Beilun WU1, G.Bastien1, M. Taupin1,2, D. Aoki1,3, D.Braithwaite1,G.Knebel1, J.Flouquet1 and J.P. Brison1
1
Univ. Grenoble Alpes, INAC, Pheliqs, F-38000 Grenoble, France and CEA, INAC, Pheliqs, F38000 Grenoble, France
2
TU Wien, Freihaus, Gelber Bereich, 8.OG Wiedner Hauptstraße 8-10 , 1040 Wien,
Österreich
3
We present our transport study on the upper critical field of the orthorhombic
ferromagnetic superconductor UCoGe.
The bulk upper critical field curves at ambient pressure are obtained by thermal
conductivity measurements for magnetic field H along all three crystal axes. For H//b
in particular, the S-shape re-entrance phenomenon is well observed, and even more
strongly than on resistivity measurements [1]. Surprisingly, for field above 8T along
the b axis, bulk superconductivity appears to be “more robust” than observed on
resistivity measurements: this is reminiscent of observations on cuprates High-Tc
superconductors, where it was taken as a demonstration of the existence of a (resistive)
vortex liquid phase.
We also present our resistivity results under pressure up to 10.5GPa in a magnetic
field along the easy magnetization axis H//c. The superconductivity domain extends
up to 4GPa and the upper critical field is probed in the whole SC phase.
These results seem to be completely at odds with analysis in the framework of the
usual orbital and paramagnetic limitation of the upper critical field. We show instead
that, as suggested by various theoretical models for ferromagnetic superconductors,
(see theory of V.Mineev [2], and model of Y.Tada [3]), these results strongly support
a magnetic field dependence of the SC coupling constant. We show that the anisotropy
and the anomalous curvatures of the H𝑐2 curves at zero pressure, as well and the
evolution of H𝑐2 // c under pressure, are consistently understood with a simple field
dependence of the pairing strength. The validity of the model is further checked by
specific heat measurements under field. It points out the major role of ferromagnetic
fluctuations in the pairing mechanism in this system.
Reference:
[1] Aoki, D.; Matsuda, T.D.; Taufour, V.; Hassinger, E.; Knebel, G. & Flouquet J.,
J. Phys. Soc. Jpn. 78, 113709 (2009).
[2] V. P. Mineev, PRB 83, 064515 (2011)
[3] Y. Tada, S. Fujimoto, N. Kawakami, T. Hattori, Y. Ihara, K.Ishida, K.
Deguchi, N. K. Sato, and I. Satoh, Journal of Physics: Conference Series 449
(2013) 012029
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Investigating the spin-triplet superconductivity of UCoGe through
Muon spin relaxation/rotation
K. Huang1, C. Tan1, J. Zhang 1, Z. Ding1, D. E. MacLaughlin2, O. O. Bernal3, K. Ishida4,
M. Janoschek5, E. D. Bauer5, A. D. Hillier6, and L. Shu1
1
Department of Physics, Fudan University, Shanghai, 200433 China
Department of Physics, University of California, Riverside, CA 92521 USA
3
Department of Physics and Astronomy, California State University, Los Angeles, CA 90032
USA
4
Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502 Japan
5
Condensed Matter and Magnet Science, Los Alamos National Laboratory, Los Alamos, New
Mexico 87545, USA
6
ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire Ox11 0QX,
United Kingdom
2
The ferromagnetic superconductor UCoGe is a prime candidate for spin-triplet
superconductivity [1]. Previous muon spin relaxation measurement (MuSR) have
shown that the ferromagnetism and superconductivity coexist macroscopically [2].
NMR Knight shift measurements have shown evidence of the ferromagnetic
fluctuations promoting superconductivity as well as a temperature independence of
the knight shift down to ~0.1 K [3, 4]. We will report recent measurements on the
Knight-Shift through transverse-field MuSR as well as zero-field MuSR
measurements on single crystalline UCoGe to even lower temperatures.
Reference:
[1] N. T. Huy et al., PRL 99, 067006 (2007)
[2] A. de Visser et al., PRL 102, 167003 (2009)
[3] T. Hattori et al., PRL 108, 066403 (2012)
[4] T. Hattori et al., JPSJ 83, 061012 (2014)
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Ferromagnetic critical behaviors in UCo1-xFexAl (x=0.02, 0.04)
single crystals
Yoshiya Homma, Dexin Li, Ai Nakamura, Fuminori Honda, Dai Aoki
The discovery of superconductivity in the uranium ferromagnetic (FM) compounds
such as UGe2, URhGe and UCoGe opened up a new paradigm of superconductivity[1],
since former unconventional superconductivity has been discovered in the vicinity of
an antiferromagnetic phase. These itinerant FM phases exhibit a similarthreedimensional T-H-P (temperature - magnetic field – pressure) phase diagram.Here, FM
transition temperature is suppressed by applying pressure and changes fromthe
second-order to the first-order transition at a tricritical point (TCP) and reaches a
quantum transition point (QTP) at zero temperature. The QTP of a first-order quantum
phase transition without criticality differs from the so-called quantum critical point
(QCP) as a second-order quantum phase transition.
UCoAl with the hexagonal ZrNiAl-type structure is a terminal material of
developing the itinerant FM. At ambient pressure, its ground state is paramagnetic
(PM), whereas the weak external magnetic field of about 0.6 T leads to a first-order
metamagnetic transition. FM phase is also induced by substitution of other d-metals
in the Co sublattice. FM state can be easily achieved by iron doping in the UCo1xFexAlabove as small as x=0.01 [2]. For x=0.01 and 0.02, the NQR spectra show the
coexistence of the PM and FM components without continuous shifts, indicating the
first-order FM transition [3]. A second-order phase transition is predicted by much
more iron content from T-H-P phase diagram based on the framework of a
simplemean-field theory [4].
We prepared UCo1-xFexAl single crystals for x=0.02 and 0.04 by the Czochralski
method by using a tetra-arc furnace. A strong uniaxial FM anisotropy along the c-axis
of the hexagonal structure has been observed in the magnetization curves below Tc
=22 and 26 K for x=0.02 and 0.04, respectively. But clear phase transition has not
been detected in the specific heat for x=0.04, where small swelling appear at around
24 K. A strong frequency dependence in the AC susceptibility suggests the secondorder FM phase transition for x=0.04. Therefore, TCP seems to exist between x=0.02
and 0.04. We will discuss critical behaviors of the itinerant FM system in comparison
with the reported data of UCo1-xFexAl [5].
Reference:
[1] D. Aoki et al., J. Phys. Soc. Jpn. 81, 011003 (2012).
[2] A.V. Andreev et al., Physica B 239, 88 (1997).
[3] K. Karube et al., Phys Rev. B 91, 075131 (2015).
[4] D. Belitz et al., Phys Rev Lett. 94, 247205 (2005).
[5] A.V. Andreev et al., J. Nuc. Sci. & Tec. Supple. 3, 172 (2002).
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Magnetism and Superconductivity in URhGe and UGe2
M. Kepa1, C. Lithgow1, A. D. Huxley1
1
Center for Science at Extreme Conditions, University of Edinburgh, EH9 3FD, UK
The paring mechanism giving superconductivity in the above ferromagnets [1]
isinvestigated with ultra-sound and Hall measurements and by torque magnetometry.
Superconductivity is linked with a jump in the magnetization in UGe2 and areorientation of the moments in URhGe. The identification of the prevalent
magneticfluctuations close to these transitions is central to a full determination of the
pairingmechanism. Our results elucidate the identity of these fluctuations.
For UGe2 this is done by fitting the data to a simple two-component mean-field
modelfor the magnetization that can explain the jump in magnetization and ultrasoundmeasurements. The strength of the fluctuations is manifest in the data as a
criticalcontribution on top of the mean field part. For URhGe the longitudinal and
transversecomponents of the magnetic response are compared and the results
discussed in thecontext of their respective contributions to pairing.
Reference:
[1] A. D. Huxley, Physica C, 514, 368-377 (2015)
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Novel 5f electric structure of antiferromagnetic USb2 studied by
angle-resolved photoemission spectroscopy
Shiyong Tan, Donghua Xie, Wei Feng, Wen Zhang, Yun Fang, Xincun Lai1*
1
Institute of Materials, China Academy of Engineering Physics, 621908, Jiangyou, China
Antiferromagnetic USb2 (TN ～203 K) is an excellent candidate to study the 5f
electronic structure, as it is a moderately correlated electron system with a quasi-2D
electronic structure. Using helium discharging light source, we obtain the Fermi
surface topology and complete band structures over the entire Brillouin zone for the
first time. The observed valence bands and low energy electronic structure agree well
with the first principle calculations in the literature. While the 5f band around M point
shows weak dispersion and is itinerant, we observe two straight-line shaped bands at
-20 meV and -60meV below EF. These two bands can be seen over the entire Brillouin
zone, which are angular independent, indicating that these two bands are localized 5f
electron bands. Possible Fermi surface nesting condition and partially opened gaps
were observed on the 5f electron bands of USb2. The gaps are found to be associated
with the antiferromagnetic transition in USb2. At 220 K and 205 K above the
antiferromagnetic transition temperature, there is no gap. When the temperature is
reduced, clear gaps can be observed at 185 K, 150 K, 110 K and 80 K below transition
temperature, the gap size increases slightly with decreasing temperature. Our results
provide important information about the 5f electronic structure, magnetic properties
and the complex emergent states in USb2.
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Hall coefficient measurement on a Toroidal Magnetic Ordered State
of UNi4B
H. Saito1, N. Miura1, C. Tabata1, H. Hidaka1, T. Yanagisawa1, and H. Amitsuka1
1
Graduate School of Science, Hokkaido University, Sapporo, Japan
Toroidal moment is one of the parameters that describe the strength of the
magnetoelectric effect. In the last several years, the toroidal order, which is the
ordered periodic array of toroidal moments, has attracted much interest in connection
with multiferroic insulating materials. Recently, S. Hayami et al. showed theoretically
that such an exotic order can occur also in metallic systems, and exotic phenomena
such as magnetization induced by electric current can occur in the toroidal ordered
metal [1].
UNi4B crystalizes in the orthorhombic structure (symmetry: Cmcm, D2h17, No.
63)[2]. Below TN( = 20.4 K ), it orders antiferromagnetically in a magnetic structure
where the magnetic momentscarried by the 2/3 of U ions make the vortices in each
triangular planes [3]. This magnetic structure is the same as that assumed in the above
theory. Our recent measurements of magnetization under electric current showed that
electric current induce magnetization in the toroidal magnetic ordered state of
UNi4B[4]. Thus the validity of the theory is confirmed in part by the experiments.
In order to make a further test for the theory, Hall coefficient measurements are
performed for the first time. The theory predicts Hall voltage which is proportional to
the square of the electric current, I2 is induced by in-plane current even in the null
magnetic field. However, such a behavior of the Hallvoltage is not observed in the
accuracy of our measurements.
Reference:
[1] S. Hayami et al., Phys. Rev. B 90, 024432 (2014).
[2] Y. Haga et al., Physica B 403 900-902 (2008).
[3] S. A. M. Mentink et al., Phys. Rev. Lett. 73, 1031 (1994).
[4] H. Saito et al., JPS autumn meeting, 9aBK-13 (2014).
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Transport Properties of Uranium Antiferromagnet URhIn5
Y. Haga1, Y. Matsumoto2, N. Tateiwa1, J. Pospíšil1, E. Yamamoto1, Z. Fisk1,3, T. Yamamura4
1
Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, Japan
2
Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, Japan
3
4
URhIn5 crystallizes in the tetragonal HoCoGa5-type structure. Unlike the
isostructural and isoelectronic compound URhGa5, URhIn5 has In as a constituent
element instead of Ga. Reflecting the larger atomic size of In than Ga URhIn5 has
significantly larger unit cell volume and hence larger interatomic U-U distance. The
appearance of magnetic ordering URhIn5 is considered to be due to relatively localized
5f states, in contrast to the nonmagnetic ground state of URhGa5. [1] It istherefore
interesting to investigate differences in the electronic states in both compounds to
reveal origin of magnetic moment in 5f electron system. We report detailed resistivity
and Hall effect measurements on URhIn5. A distinct change in the Hall coefficient is
observed below the Néel temperature, suggesting that majority ofthe Fermi surface is
gapped in the ordered state. The result will be compared with Fermi surfaces observed
by the de Haas-van Alphen effect. [2]
Reference:
[1] Y. Matsumoto et al., Phys. Rev. B 88, 045120 (2013).
[2] Y. Matsumoto et al., JPS Conf. Proc. 3, 011097 (2014).
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Electronic tuning of URu2Si2 through P and Ga substitution
R. E. Baumbach1, A. Gallagher1, K. W. Chen1, S. Cary2, F. Kametani3, D. Graf1, T. AlbrechtSchmitt2, S. C. Riggs1, and A. Shekhter1
1National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida,
USA 2Florida StateUniversity, Dept. of Chem. And Biochem., Tallahassee, Florida, USA
3Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida
State University, Tallahassee, Florida, USA
Materials that straddle the boundary between itinerant and local electronic behavior
are exemplary hosts for novel phenomena, including unconventional
superconductivity, anomalous magnetism, non-Fermi liquid behavior, and exotic
electronic phases. The 5f-electron intermetallic URu2Si2 is a well-known example,
exhibiting an exotic ordered state (``hidden order'') and unconventional
superconductivity. We report a study of URu2Si2 using the new tuning parameter,
ligand site substitution Si →L (L= Ga and P). While phosphorous substitution quickly
suppresses both hidden order and superconductivity [1], gallium substitution has a
mild effect, illustrating the marked difference between electron- and hole-doping on
the ligand site. To disentangle these phenomena, we performed electrical transport and
thermodynamic measurements. Electrical transport measurements in high magnetic
fields are particularly illuminating, and provide insight into the evolution of the
anomalous magnetoresistance, Fermi surface topology, electronic effective masses,
and g-factor anisotropy. We discuss trends in these quantities for electron- and holedoping and their implications for unraveling the behavior of URu2Si2.
Reference:
[1] A. Gallagher et al., Nature Communications, manuscript accepted (2016)
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Unusual Magnetic Order of UAu2Si2 Studied by 29Si-NMR
C. Tabata1, Y. Ihara1, S. Shimmura1, N. Miura1, H. Saito1, H. Hidaka1, T. Yanagisawa1, and H.
Amituaka1
1Graduate School of Science, Hokkaido University, Sapporo, Japan
The low-temperature-ordered state below 19 K of UAu2Si2 has been left
unidentified for about 30 years, receiving much less attention than those of other
UT2Si2 relatives. Recently, we have revisited this compound through detailed
investigation of its thermal, magnetic, and transport properties by means of
macroscopic measurements, and obtained some indications that a certain type of
antiferromagnetic order occurs below 19 K, contrary to the ferromagnetic one
suggested in the previous reports [1-3]. In order to get microscopic information of this
magnetic order, we performed 29Si-NMR measurements on powdered UAu2Si2 for
the first time. The obtained NMR spectra strongly suggest an uncompensated
antiferromagnetic order with q = (2/3, 0, 0) as the most likely magnetic structure of
this compound.
Reference:
[1] T. T. M. Palstra et al., J. Magn. Magn. Mater. 54-57, 435 (1986).
[2] M. S. Torikachvili et al., J. Magn. Magn. Mater. 104-107, 69 (1992).
[3] K. J. Lin et al., Solid State Commun. 103, 185 (1997).
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Large single crystal growth of compounds with high vapor pressure
elements
C. D. Cao
Department of Applied Physics, Northwestern Polytechnical University, Xi’an 710072, P.R.
China
Single crystals are very important for fundamental scientific research in the
condensed matter physics field. Normally it is difficult to use conventional methods
to grow single crystals of the compounds with high vapor pressure elements.
Especially, the vapor pressure of Eu attains 144 Pa at its melting point, 822 C, and
its boiling point is only 1597 C.In this work, large single crystals (6 mm in diameter
and up to 45 mm in length) of CeCu2Si2, EuCu2Si2, Eu2CuSi3, Eu2PdSi3 and Cr doped
YMnO3compounds have been grown by using a vertical floating zone method with
optical heating. Elevated pressures up to 12 MPa of Ar atmosphere in the growth
chamber were employed, which can suppress to a large degree the evaporation from
the molten zone.However, evaporation during growth can not be avoided completely
because the liquidus temperatures of these compoundsare very high. It is found that
the suppression of evaporation of volatile elements and control of the floating zone
temperature are the key factors for the stability of the growth process and a relatively
low travelling velocityand a short length of the floating zone play an important role in
phase selection and formation of a single crystal. The growth parameters, structures,
and perfection of the crystals are discussed. The magnetic and electron transport
properties are compared with polycrystals or single crystals grown with other methods.
Keywords: single crystal growth, high vapor pressure element, floating zone
technique
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Spin polarization measurements in ferromagnetic SrRuO3 using
point-contact Andreev reflection technique
M.Shiga1, N.Nishimura1, Y.Inagaki1, T.Kawae1, H.Kambara2, K.Tenya2
1
Department of Applied Quantum Physics, Kyushu University,
2
Department of Education, Shinshu University
Using the point-contact Andreev reflection (PCAR) technique, we have performed
spin polarization measurements in a polycrystalline SrRuO3 to study the difference of
the spin polarization between the ballistic and diffusive transport samples. SrRuO3
exhibits ferromagnetic transition at T = 160 K with the saturation moment of 1.6μB.
PCAR were measured with Pb tips for 2 KT4.2 K with changing the contact area
mechanically. The results were well fitted by the modified Blonder-Tinkam-Klapwijk
(BTK) model. We estimate the spin polarization P ~ 0.60, which is slightly larger that
of a single crystal film with P ~ 0.52.
Reference:
[1] P.Raychaudhuri et al., PRB 67, 020411(R) (2003)
[2] I.I.Mazin et al., JAP 89, 7576 (2001)
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The true fourth fundamental circuit elements based on
magnetoelectric effects
Y. S. Chai1, D. S. Shang1, , Z. X. Cao1, J. Lu1, S. H. Chun2, K. H. Kim2, Y. Sun1
1
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics,
2
CeNSCMR, Department of Physics and Astronomy, Seoul National University, Seoul 151747, South Korea
In addition to resistor, capacitor and inductor, Chua proposed in 1971 the fourth
fundamental circuit element to directly relate magnetic flux ϕ and charge q1. Such a
circuit element, dubbed memristor1,2, was later attributed to the non-linear currentvoltage characteristic and has been realized in various material structures3. Here we
clarify that the memristor in this sense is not the true fourth fundamental circuit
element, but the nonlinear extension to the concept of resistor, in analogy to the
extension of memcapacitor to capacitor, and meminductor to inductor4. Instead, a twoterminal device employing magnetoelectric effect possesses the function of relating
directly ϕ and q. Both the linear and the memory devices having this function, dubbed
transtor and memtranstor, respectively, are realized by sandwiching a magnetoelectric
hexaferrite crystal in electrodes. Moreover, the devices can operate either in the
charge-driving mode or in the flux-driving mode, and the transtance arising from the
magnetoelectric coefficient can be both positive and negative, thus displaying a
butterfly-shaped, pinched hysteresis loop. With the introduction of transtor and
memtranstor, a complete and harmonized relational graph can be constructed for the
fundamental circuit variables, which will be very helpful for developing more novel
circuit functionalities in future5.
Reference:
[1] Chua, L. O. IEEE Trans. Circuit Theory 18, 507-519 (1971).
[2] Chua, L. O. & Kang, S. M. Proc. IEEE 64, 209-223 (1976).
[3] Strukov, D. B., Snider, G. S., Stewart, D. R., & Williams, R. S. Nature 453, 8083 (2008).
[4] Ventra, M. D., Pershin, Y. V., & Chua, L. O. Proc. IEEE 97, 1717-1724
（2009）
[5] Shang, D.-S., Chai, Y.-S., Cao, Z.-X., Lu, J. & Sun, Y. Chin. Phys. B 24,068402
(2015). Chen et al., PRL 114, 146403 (2015)
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Large-N analysis of the multicritical behavior of the topological
Ginzburg-Landau theory of self-dual Josephson junction arrays
S. Sakhi
Department of Physics, American University of Sharjah, Sharjah, UAE
The continuous quantum phase transition (QPT) in Josephson junction arrays
systems (JJA) provides an ideal example to study quantum fluctuations at zero
temperature. Near a quantum critical point (QCP), scale invariance and universality
emerge, and the long-distance low energy properties of the system are characterized
by critical exponents which are insensitive to the microscopic details of the model. A
topological two-field Ginzburg-Landau theory interacting through gauge fields was
introduced in [1] as a phenomenological model to study the QPT in JJA systems. Here
I investigate the phase structure of a gauged U(N)×U(N)-symmetric model with selfinteractions of the form (Φ*Φ)³ and interacting with a mixed Maxwell-Chern-Simons
term in threedimensional space-time. Combining the renormalization group method
with a controlled large N generalization of the model, I carry out a systematic 1/N
expansion in order to analyze the nature of the multicritical behavior. I also study the
structure of the minimum of the quantum effective potential in order to obtain
information about the phase diagram and the beta function of the scalar fields coupling
beyond the leading order.
Reference :
[1] S. Sakhi, Physical Review D, 90, 045028 (2014)
352
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An efficient continuous-time quantum Monte Carlo impurity solver
in Kondo Regime
Changming Yue1, Yilin Wang1, Xi Dai1,2
1
2
Institute of P hysics, Chinese Academy of Sciences, Beijing 100190, China
Collaborative Innovation Center of Quantum M atter, Beijing 100190, China
An efficient continuous-time quantum Monte Carlo impurity solver with
high acceptation ratio at low temperature is developed to study the strongly
cor-related heavy-fermion materials. In this solver, the imaginary time
evolution operator for the high energy multiplets, which decays very rapidly
with time, is approximated by a δ function, and as a result the virtual charge
fluctuations of fnfn±1 are all included without applying SchriefferWolfftransformation explicitly . As benchmarks, our algorithm perfectly
reproduces the results for both Coqblin-Schriffeer and Kondo lattice models
obtained by ct-J method developed by JunyaOtsuki et al. Furthermore, it
allows us to study low energy physics of heavy-fermion materials directly
without fitting the exchange cou-pling $J$ in the Kondo model. As an
example, we test our solver on CeCoIn5, the famous heavy fermion material
within the framework of LDA+DMFT to obtain its quasi-particle spectrum.
353
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Global phase diagram and single particle excitations in Kondo
insulators
J. H. Pixley1, Rong Yu2, 3, Silke Paschen4, and Qimiao Si5
1
Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics,
University of Maryland, College Park, Maryland 20742- 4111 USA
2
Department of Physics, Renmin University of China, Beijing, 100872, China
3
Department of Physics and Astronomy, Collaborative Innovation Center of Advanced
Microstructures, Shanghai Jiaotong University, Shanghai 200240, China
4
Institute of Solid State Physics, Vienna University of Technology, WiednerHauptstraße 8-10,
1040 Vienna, Austria
5
Department of Physics & Astronomy, Rice University, Houston, Texas, 77005, USA
Motivated by quantum criticality in Kondo insulators [1] tuned by pressure or
doping we study the effects of magnetic frustration and the properties of the single
particle excitations in a Kondo lattice model [2]. Focusing on the Kondo insulating
limit we study the Shastry-Sutherland Kondo lattice and determine the zero
temperature phase diagram, which incorporates a valence bond solid,
antiferromagnet, and Kondo insulating ground states, with metal-to-insulator
quantum phase transitions. We argue that this phase diagram is generic and represents
a “global” phase diagram of Kondo insulators in terms of quantum fluctuations and
the Kondo interaction. We then focus on the momentum distribution of single particle
excitations within the Kondo insulating ground state. We show how features of the
Fermi-surface of the underlying conduction electrons appear in the Kondo insulating
phase. Lastly, we discuss the implications of our results for quantum criticality in
Kondo insulators [1] as well as for the recent de Haas-von Alphen measurements in
the Kondo insulator SmB6 [3,4].
References:
[1] Q. Si and S. Paschen, physica status solidi (b) 250, 425 (2013).
[2] J. H. Pixley, et. al., arXiv:1509.02907 (2015).
[3] B. Tan et al, Science 349, 287 (2015).
[4] G. Li et al, Science 346, 1208 (2014).
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Quantum criticality in Kondo quantum dot coupled to helical
edge states of interacting 2D topological insulators
Chung-Hou Chung1,2,* and Salman Silotri1
1
Department of Electrophysics, National Chiao-Tung University, HsinChu, Taiwan, 300, R.O.C.
2
Physics Division, National Center for Theoretical Sciences, HsinChu, Taiwan 300, R.O.C.
We investigate theoretically a novel quantum phase transition (QPT) between the
one-channel Kondo (1CK) and two-channel Kondo (2CK) ground states in a quantum
dot coupled to helical edge states of interacting 2D topological insulators (2DTI) by
tuning Kondo couplings at a fixed Luttinger parameter K<1[1]. The exotic non-Fermi
liquid 2CK state has been predicted in a Kondo impurity embedded in two
conventional Luttinger liquid leads in the limit of strong electron-electron
interactions (for K<1/2) since 1990’s[2]. However, the expected 1CK-2CK QPT at
K=1/2 has not been addressed due to the difficulty arising from the strong-coupling
nature of 2CK state. We address this long-standing issue in a slightly different context
via a new theoretical approach by combining acontrolled perturbative
renormalization group (RG) technique with bosonization and re-fermionization
mappings near weak-coupling (1CK) and strong-coupling (2CK) fixed points of our
model system.
Depending on the strength of electron interactions (measured by K) and various
Kondo couplings in the effective anisotropic two-channel Kondo model, we find the
2CK fixed point can be unstable towards the 1CK fixed point and the system is
expected to undergo a quantum phase transition between 1CK and 2CK fixed points.
We extract quantum critical and crossover behaviors from various observables near
criticality. Our system serves as the first example of the 1CK-2CK QPT accessible
theoretically by the controlled RG approach and sheds light on the two-decade long
issue of exotic QPT in Kondo dot coupled to conventional Luttinger liquids. Our
results are relevant for the newly discovered helical Luttinger liquid in topological
insulators made of Ga/As In/Sb quantum well structures[3] as well as for a dissipative
quantum dot[4].
References:
[1] Chung-Hou Chung*, Salman Silotri, New Journal of Physics, 17, 013005(2015).
[2] M. Fabrizio and AO Gogolin, Phys. Rev. B 51, 17827 (1995).
[3] R. Du et al., 2015 APS March Meeting talk (un-published).
[4] Chung-Hou Chung*, Karyn Le Hur, Gleb Finkelstein, Matthias Vojta, and
Peter Woelfle, Phys. Rev. B, 87, 245310-245349 (2013); Chung-Hou Chung*,
Karyn Le Hur, Gleb Finkelstein, Matthias Vojta, and Peter Woelfle, Phys. Rev.
Lett. 102, 216803 (2009); H. Mebrahtu et al., Nature (London)488, 61 (2012).
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Quantum lattice models: Ground state and low-lying excitations.
Ilyas Noor Bhatti1
1
Address: Physics Department, Jamia Millia Islamic, New Delhi 110025. India
Quantum lattice models like Hubbard model,t-J model,Heisenberg spin model
[1,3,4],have been extensively used in condensed Matter physics to understand novel
phenomenq,s like Magnetism, metal-insulator transition and Superconductivity.
Analytically exact results for some of these models have been found in one-dimension
[2, 4] which have only limited applicability to real problems [5, 6, 7, 8, 9, 10, 11].
These models have been numerically studied in two dimensions using various
techniques like Exact Diagonalization(ED), Quatum Monte Carlo, Dynamical MeanField Theory, etc. [12, 13]. Hubbard model is the simplest lattice model to incorporate
electron-electron correlation insystems with spin as well as charge degrees of freedom.
It has a hopping term as well as an interaction ter . It was proposed [1] in early 1960 ’s
and initially applied to understand the behavior of transition metal oxides, compounds
which are antiferromagnetic insulator, yet predicted to be metal. The Hubbard model
has also been used in the understanding of heavy fermion systems. Despite its
simplicity, it exhibits behavior relevant to some of the most subtle properties of solid
state systems. The t − j model is derived [3] from the Hubbard model to discribe
strongly correlated electron systems. It has been used to understand high temperature
superconductivity in doped antiferromagnets. In the Heisenberg spin model [4], spins
are treated quantum mechanically obeying angular momentum algebra. Spin- 12
particles are described using Pauli matrices. The Heisenberg model is used in the study
of phase transitions of magnetic systems. A powerful method to study the above lattice
models in two and higher dimensions is exact diagonalization (ED) of the Hamiltonian
matrix to find the ground state and low-lying excited states for a finite lattice. The
Quantum Monte Carlo can study a larger lattice, but suffers from the well-known sign
problem at low temperatures[12]. Another powerful method being currently used to
study strongly correlated systems is Dynamical Mean Field Theory (DMFT) [13]. An
attempt will be made to develop and implement variants of these schemes to study
phase diagrams in parameter space for the above models.
References:
[1] J. Hubbard, Proc. Royal. Soc . Sec. A 276, 238(1963); 277, 237(1964); 281, 401
(1964)
[2] Elliott H. Lieb and F. Y. Wu Phys. Rev. Lett. 20,25, (1968)
[3] F.C. Zhang and T. M. Rice, Phys. Rev. B 37, 3759, (1988)
[4] H. A. Bethe, Z. Phys. 71, 205 (1931)
[5] P. W. Anderson, Science 235, 1196 (1987).
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Antiferromagnetism and metamagnetic transitions in EuNi5As3
W. B. Jiang1, J. M. Chen2, M. Smidman1, C. Y. Guo1, J. Y. Liu3, W. Xie1, B. Shen1,
H. Lee1, X. Lu1,4, H. Q. Yuan1,4
1
Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou,
China
2
National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
3
Department of Chemistry, Zhejiang University, Hangzhou 310027, China
4
Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
We have successfully synthesized single crystals of EuNi5As3 using a flux method
and present a systematic study of the crystal structure, physical properties and
electronic structure from measurements of single crystal x-ray diffraction, magnetic
susceptibility, specific heat, electrical resistivity, thermoelectric power and X-ray
absorption spectroscopy. EuNi5As3 undergoes two close antiferromagnetic (AFM)
transitions at TN1=7.1K and TN2=6.5K, which is associated with the Eu2+ moments. At
2K, below these two AFM transition temperatures, two successive metamagnetic
transitions at 0.44T and 0.74T are observed, which are strongly coupled with TN1 and
TN2 respectively, when the magnetic field is applied along the a axis. Furthermore,
another weak crossover occurs at 2.41T for fields applied in the bc plane. Upon
applying magnetic fields, TN1 and TN2 are both gradually suppressed to lower
temperatures, eventually forcing the system into the spin-polarized paramagnetic state.
Measurements of the valence will also be discussed, which show that the Eu ions exist
in the divalent state, as expected for magnetically ordered Eu based compounds.
Reference:
[1] J. V. Badding et al., Phy. Rev. B 35, 8880(R) (1987)
[2] R. A. Fisher et al., Phy. Rev. B 52, 13519 (1995)
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Doping induced decayed dimensionalities of the magnetic order in
DyFe1-xInxO3
Ya Yang1, Yabei Wu1, Wei Ren1, Jincang Zhang1, Shixun Cao1*
1
Department of Physics, Shanghai University, Shanghai 200444, China
Phone: +86-21-6613-2529, Fax : +86-21-6613-4208, *E-mail:
[email protected]
Abstract
A series of DyFe1-xInxO3 (x = 0 to 1 step 0.1) polycrystalline samples have
been prepared by solid reaction methods. The crystal structure, refined by the
Fullprof, shows that the lattice constants change by the In ions doping, which
indicates that the results would be divided into the orthorhombic one in the
case of 0≤x≤0.6 and the hexagonal one in the case of 0.7≤x≤1 resulting in a
huge distortion of the magnetic sublattice. The magnetization data also has
been obtained for all the samples in the temperature range from 3 K to 300 K.
The pure DyFeO3 sample undergoes a spin reorientation transition around 50
K, while the introduced In ions make a complex effect on the phase transition.
Firstly, the nonmagnetic In ions would destroyed the original Fe-Fe coupling,
namely the canted antiferromagnetic structure which leads to an increasing of
the net magnetization lying along the c axis. Nevertheless, the excess In ions
would eventually dilute the original magnetic system and weaken the total
magnetization. Secondly, the doped In ions raise the temperature of spin
reorientation for the x = 0.1 and subsequently have little influence to the
samples of the 0.2≤x≤0.6. However, thesubstitution still retained the spin
reorientation transition phase for the x = 0.7 and 0.8. We developed a
formalism based on molecular theory, which may give an explanation of the
changes in the spin-reorientation temperature by the In-doping. Then, by
performing ab initio density functional theory (DFT) calculation, we study the
role of the 4d10 -In3+ ions in the altering of DyFeO3 magnetic orders. By the
means of non-collinear calculation, we find that the in-plane interaction among
the Fe3+ ions. Furthermore, our findings indicate a type of Γ4 - Γ2 transition
exists in the hexagonal Fe-In magnetic systems which directly point to a 2
dimensionalities magnetic order.
Keywords: Perovskite, Spin reorientation, Dimensionality
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Tuning competing ground-states in LuFe4Ge2 using external
pressure
M. O. Ajeesh1, K. Weber1, R. dos Reis1, C. Geibel1, M. Nicklas1
1Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
Tuning competing ground-state properties using external pressure has attracted
much attention in current condensed matter research. This is due to the fact that exotic
phenomena and unconventional phases occur in regions of competing energy scales.
Here, we present an investigation on LuFe4Ge2 by electrical resistivity experiments
under external pressure in order to understand the interplay between competing
ground states in a frustrated, itinerant magnetic system. At ambient pressure LuFe4Ge2
orders antiferromagnetically below 32 K. The antiferromagnetic (AFM) transition is
connected with a structural transition. We have established the temperature – pressure
phase diagram: pressure suppresses the original antiferromagnetically ordered state to
zero temperature at around 1.7 GPa. Upon further increasing pressure a new pressureinduced phase emerges. This phase exhibits a qualitatively different
magnetoresistance compared with the AFM phase suggesting a different type of
ordering than at lower pressures. Furthermore, above 1.5 GPa we find a metamagnetic
transition at higher magnetic fields. The onset of this phase shifts to lower fields with
increasing pressure. Further studies to understand the nature of the new phases are on
the way.
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A novel magnetic phase transition and anisotropic interaction
induced by Mn substitution in single-crystal TbFe1-xMnxO3
Yifei Fang1, Ya Yang1, Gang Qiang1, Baojuan Kang1, Shixun Cao1, ChengtianLin2, and Jincang
Zhang1*
1
Materials Genome Institute and Department of Physics, Shanghai University, Shanghai
200444, China
2
Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart,
Germany
Correspounding author, E-mail:[email protected]
Abstract: We report an observation of an peculiar spin reorientation
from （
to （
1 Ax, Gy, Cz）occurred at high temperature of 254 Kand
4 Gx, Ay , Fz）
areversed phenomenon from （
at low temperature of
1 Ax, Gy, Cz）to （
4 Gx, Ay , Fz）
15.5 K in the TbFe1-xMnxO3 sample doped with Mn~0.25. The original Γ2 phase in
TbFeO3 disappears in x>0 sample. These results were verified by both magnetization
and neutron diffraction measurements. Meanwhile, it is showed that the spin
reorientation temperature increases from 8.5 to 299 K along with x raising from 0 to
0.6. These phenomena are related to the strong variation of the anisotropy field. The
variation of magnetic entropy between and axes indicates the change of
magnetocrystalline anisotropy energy in the TbFe1-xMnxO3 system. The above
phenomenon can be explained by the spin glass state which is caused by Mn
substitution. Furthermore, as Jahn-Teller active Fe3+ is partially substituted with JahnTeller inactive Mn3+, various anisotropy interactions, such as Dayaloshinskii-Moriya
interaction, superexchange interaction, and Jahn-Teller interaction, compete with
each other, giving rise to a rich magnetic phase diagram. The large magnetocaloric
effect shows the material is a potential magnetic refrigerant. These findings provide
an insight into the nature of spin reorientation phenomenon and an alternative
realization of spin-switching devices at room temperature in the rare-earth
orthoferrites.
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Magnetic transitions on pseudoternary compounds Ho1-xYxRh2Si2
T. Shigeoka1, T. Fujiwara1, Y. Uwatoko2
1Graduate School of Science and Engineering, Yamaguchi University, Yamaguchi,
Japan
2 Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba, Japan
The ternary compound HoRh2Si2 shows so called “successive component-separated
magnetic transitions”; the c- and ab-components of the magnetic moments of Ho3+
independently order at different temperatures, TN1=29.1K and TN2=12.1K,
respectively [1]. Such transitions often appear in frustration systems. Complex
magnetization processes were observed at low temperatures [2]. This compound has
an additional transition at Tt=27.3 K where the magnetic structure changes. These
behavior should be affected by magnetic interactions. In order to elucidate the role of
magnetic interactions for this behavior, magnetic behavior of Ho1-xYxRh2Si2 has been
investigated by measurements of magnetization and magnetic susceptibility. Figure 1
shows the composition x dependence of the magnetic transition temperatures TN1, TN2,
and Tt. Both transitions TN1 and TN2 decrease with increasing x quadratically. On the
other hand, the transition Tt changes by a linear function for x. The magnetic ordering
temperature is persisted for high x, indicating the Ho moments is able to order in spite
of very week interaction in this system. The partial ordered state of TN2<T<TN1,
frustration state, is stable for high x. This indicate some magnetic interactions may be
important role for the frustration.
Fig. 1 Composition x dependence of magnetictransitions on Ho1-xYxRh2Si2
Reference:
[1] T. Shigeoka, et al., J, Phys. Conf. Ser. 273, 012127 (2011)
[2] T. Shigeoka, et al., J, Phys. Conf. Ser. 391 012063 (2012)
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Anomalous Antiferromagnetic Phase Diagram in HoRu2Al10
S. Kamikawa1，I. Ishii1，H. Goto1，K. Takezawa1, F. Nakagawa1，H. Tanida1，M.
Sera1 and T. Suzuki1,2,3
1Department of Quantum Matter, ADSM, Hiroshima University, Higashihiroshima, Japan
2Institute for Advanced Materials Research, Hiroshima University, Higashihiroshima, Japan
3Cryogenics and Instrumental Analysis Division, N-BARD, Hiroshima University,
Higashihiroshima, Japan
The ternary compound HoRu2Al10 has the orthorhombic YbFe2Al10-type structure
(space group: Cmcm) [1]. HoRu2Al10 shows a sharp peak of specific heat at TN = 5.0
K in zero-magnetic field [2]. In the temperature dependence of magnetic susceptibility,
a cusp is observed at TN indicating an antiferromagnetic (AFM) ordering[2]. In this
study, we performed specific heat measurements on HoRu2Al10 under magnetic fields
H. In H along b- and c-axes, the sharp peak of the specific heat shifts to lower
temperatures with increasing H. From these measurements, we found an anomalous
antiferromagnetic phase diagram in H // c. In H // b, TN decreases monotonically with
increasing H, and a phase boundary closes around 1.0 T, which is a usual behavior
for an antiferromagnet. In H // c, although TN shows a monotonic decrease with
increasing H, a phase boundary shows an inflection point around 3.0 K.
Reference:
[1] V. M. T. Thiede, T. Ebel, and W. Jeitschko : J. Mater. Chem. 8 (1998) 125.
[2] T. Mizushima, Y. Watanabe, J. Ejiri, T. Kuwai, and Y. Isikawa : J. Phys. : Conf.
Ser. 592 (2015) 012051.
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Magnetic properties of GdT2Zn20 (T=Fe, Co) investigated by x-ray
diffraction and spectroscopy
J. R. L. Mardegan1,2, S. Francoual2, G. Fabbris3,4,5, L. S. I. Veiga1, J. Strempfer2, D. Haskel3,
R. A. Ribeiro6, M. A. Avila6, and C. Giles1
1
Instituto de Física “Gleb Wataghin,” Universidade Estadual de Campinas, Campinas – SP,
Brazil
2
Deutsches Elektronen-Synchrotron DESY, Hamburg - HH, Germany
3
Advanced Photon Source, Argonne National Laboratory, Argonne - IL, USA
4
Department of Physics, Washington University, St. Louis – MO, USA
5
Department of Condensed Matter Physics and Materials Science, Brookhaven National
Laboratory, Upton - NY, USA
6
CCNH, Universidade Federal do ABC (UFABC), Santo André– SP, Brazil
The family of complex intermetallic compounds RT2Zn20 (R = rare earth, T =
transition metal) has attracted great attention due to particular properties such as a
remarkably high magnetic ordering temperature observed for T = Fe (although it
contains less than 5% of R ion) and a nearly ferromagnetic Fermi-liquid behavior
observed in YFe2Zn20.[1-3]However, the microscopic properties have not been fully
investigated yet.
We investigated the magnetic and electronic structures at low temperature of the
GdT2Zn20 (T = Fe, Co) compounds using the x-ray resonant magnetic scattering
(XRMS) and magnetic circular dichroism (XMCD) techniques. GdCo2Zn20 is found
to order into a commensurate antiferromagnetic magnetic structure with q = (½ ½ ½)
magnetic propagation vector below TN = 5.72(6) K. The Gd magnetic moments order
following the magnetic representation Γ6 with a PS-1 magnetic space group [4].
GdFe2Zn20 shows a strong magnetic dichroic signal below the Curie temperature (TC
= 85(2) K) at both the Gd L2 and L3 edges. Surprisingly, a small magnetic signal is
detected at the Zn K-edge which suggests that the Zn ions are spin polarized by the
Gd 5d orbitals, while no magnetic contribution coming from the iron ion is observed.
This finding suggests that the rare earth ions located in this large polarized
environment are strongly affected by the Zn cages, which has a direct influence on the
electronic and magnetic properties.
Reference:
[1] M. S. Torikachvili, et al., PNAS 104, 9960 (2007).
[2] S. Jia, et al., Nature Physics 3, 334 (2007).
[3] S. Jia et al., PRB 77, 104408 (2008).
[4] J.R.L. Mardegan et al., PRB (2016) pre-print.
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Re-entrant Spin Glass Behavior and Large Magnetocaloric Effect in
Er2PtSi3
D. X. Li1, Y. Homma1, A. Nakamura1, F. Honda1, T. Yamamura2, D. Aoki1
1
Institute for Materials Research, Tohoku University, Oarai, Ibaraki, 311-1313 Japan
2
Institute for Materials Research, Tohoku University, Sendai, 980-8577 Japan
Magnetic properties of new ternary intermetallic compound Er2PtSi3 crystallizing
in theBa2LiSi3-type structure is systematically studied by AC susceptibility
[χ′ac(T),χ′′ac(T)], FC and ZFC magnetization [MFC(T), MZFC(T)], magnetic relaxation
[M(t)], electricalresistivity [ρ(T)] and specific heat [C(T)] measurements. It is found
that an antiferromagnetic phase transition occurs in this compound at the Néel
temperature TN=5.4 K followed by a re-entrant spin glass transition at the spin freezing
temperature Tf=2.4 K. The former is mainly manifested as the evident peaks in
MZFC(T), MFC(T), C(T)and ρ(T) curves near TN, and no abnormality in χ′′ac(T)curve
around TN. The latter is confirmed by the clear frequency dependence of the peak
temperature Tfin χ′ac(T)curve,the long-time magnetic relaxation behavior and the lack
of anomaly in C(T) and ρ(T) curves around Tf. On the other hand, Er2PtSi3 also shows
large magnetocaloric effect. The maximum value of magnetic entropy change
estimated from both magnetization and specific heat measurements is as large as
∆Smmmax~17.5 J/kg/K at the temperature just above TNfor a field change of 5 T. These
results indicate that Er2PtSi3 should be classified as a re-entrant spin glass system, and
can be considered as a candidate for low-temperature magnetic refrigeration material.
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Relationship between magnetic, electronic and structural properties
in tetragonal rare-earth rhodium borides as a function of pressure
L. S. I. Veiga1,2,3, R. D. dos Reis1,2, G. Fabbris3,4, D. Haskel4, F. G. Gandra2, N. M. SouzaNeto1
1Brazilian Synchrotron Light Laboratory (LNLS), Campinas, SP 13083-970, Brazil
2Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas (UNICAMP), SP,
Brazil
3Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439,USA
4Department of Physics, Washington University, St. Louis, Missouri 63130, USA
Among the materials presenting the interplay between superconductivity and
magnetism, the tetragonal rare earth rhodium borides RERh4B4 (RE= rare-earth) have
been investigated extensively due to two special features: the long-range magnetic
ordering traced in part to the RE sublattice and the persistence of superconductivity,
even in the presence of relatively large concentrations of RE ions [1-5]. We have used
the selectivity in element, orbital and spin-dependent electronic structure, via x-ray
magnetic dichroism in combination with x-ray diffraction to study the electronic,
magnetic and crystallographic properties of RERh4B4 (RE=Dy and Er) system as a
function of pressure. Our magnetic dichroism (XMCD) data on Dy and Er L3
absorption edges show a progressively decrease of the dipolar (2p -> 5d) and
quadrupolar (2p -> 4f) contributions as a function of pressure. In the the pressure range
between 20 – 25 GPa, we observed the disappearance of features in the non-magnetic
x-ray absorption spectra (XANES) for both compounds although the x-ray diffraction
patterns do not show any changes in the crystal structure in the entire pressure range
measured (1 – 40GPa). These results highlight a possible relationship between the
magnetic and electronic structure with the atoms arrangement in the first coordination
spheres which, in turn, does not result in changes in crystal lattice and/or space group.
References:
[1] B. Maple, Physica B 215, 110-126 (1995)
[2] B. T. Matthias, et al., Science 175, 1465-1466 (1972)
[3] B. T. Matthias, et al., Proc. Natl. Acad. Scie. USA, 74, 1334-1335 (1977)
[4] W. A. Fertig et. al., Phys. Rev. Lett. 38, 987 (1977)
[5] “Supercondutivity in Ternary Compounds II: Supercondutivity and Magnetism”.
Edited by M. B. Maple and O. Fischer, 1982
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Soft X-ray Photoemission Study on Sr1-xLaxRuO3
I. Kawasaki1, Y. Sakon2, S.-i. Fujimori3, H. Yamagami3,4, M. Yokoyama2
1
Graduate School of Material Science, University of Hyogo, Hyogo 678-1297, Japan
2
Faculty of Science, Ibaraki University, Ibaraki 310-8512, Japan
3
Condensed Matter Science Division, Japan Atomic Energy Agency, Hyogo 679-5148, Japan
4
Department of Physics, Faculty of Science, Kyoto Sangyo University, Kyoto 603-8555, Japan
SrRuO3 is a ferromagnet with a Curie temperature of about 160 K. Photoemission
experiments showed that the density of states at Fermi level is dominated by the Ru
4d states, and the overall band structure is well reproduced by band structure
calculations [1]. Itinerant Ru 4d states are thus considered to be responsible for the
magnetic properties. However, an incoherent feature reflecting electronic correlation
effects is observed in the photoemission spectra, implying that the electronic state of
this system is not trivial.
Recently, we have investigated the electronic and magnetic properties of
Sr1−xLaxRuO3 by means of various macroscopic measurements [2]. We revealed that
the ferromagnetic order is strongly suppressed with increasing La concentration x and
that the ordered state varies from ferromagnetic to cluster-glass states for x ≥ 0.3,
demonstrating that spatially inhomogeneous magnetic states, which are indicative of
the localized character of Ru 4d states, are induced by La doping. In this study, to
understand the electronic state in the cluster-glass states, we performed soft x-ray
photoemission experiments. Our experiments showed that the incoherent feature of
the pure SrRuO3 develops with increasing La concentration, suggesting that the
electronic correlation plays an important role in the cluster-glass states.
Reference:
[1] S. Grebinskij et al., Phys. Rev. B 87, 035106 (2013)
[2] I. Kawasaki et al., J. Phys. Soc. Jpn. 83, 064712 (2014)
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Antiferromagnetic spin cluster and field-inducedspin-floptransition in S = 3/2 SrCo2(PO4)2
Arvind Yogi1, Ruta Kulkarni1, S. K. Dar1, and A. Thamizhavel1
1
Department of Condensed Matter Physics and Materials Science,Tata Institute of Fundamental
Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India
We report the magnetic and crystallographic properties of the S = 3/2 compound
SrCo2(PO4)2. This compound crystallizes in the triclinic symmetry with space group
P-1 and the crystal structure is characterized by the coupled Co dimer chains along
the
crystallographic
a-axis.
Experimentally,
SrCo2(PO4)2
orders
antiferromagnetically at TN = 8.5 K as revealed by magnetization and specific heat
measurements. The effective magnetic moment (µeff ) is calculated to be 4.753(2) µB,
which is larger than the value of 3.87 µB for S = 3/2 with a g factor of 2. Also, the
negative Weiss constant −9.969 (5) K suggests that the dominant interaction between
Co+2 ions is antiferromagnetic in nature. This higher value of µeff is observed in other
Co+2 compounds and are in good agreement with the earlier reports. We note that the
Néel temperature of 8.5 K is quite close to the Weiss constant, showing that
SrCo2(PO4)2 is a typical three dimensional (3D) Heisenberg AF system without any
frustrations. In addition, the magnetization curves, measured at temperatures well
below TN, reveal field-induced spin-flop transition at 4.5 T which suggests a large
magnetocrystalline anisotropy in the present system. Analysis of the magnetic specific
heat shows that the magnetic excitation in the SrCo2(PO4)2 compound below TN are
spin wave (s-wave) type.
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Spin Glass Behavior in BaGd2-xEuxO4 as observed from μSR
Julian Munevar1, Ekaterina Pomjakushina2, Dariusz Gawryluk2, Elvezio Morenzoni1
1
2
Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, Villigen, Switzerland
Laboratory of Development and Methods, Paul Scherrer Institut, Villigen, Switzerland
The BaRE2O4 compound family (RE = rare earth atoms) has been found to be a
potential frustrated magnet, due to its honeycomb lattice and relatively high f factors
that indicate some degree of magnetic frustration for the rare earth moments [1].
Among them, the BaGd2O4 is one of the few compounds displaying magnetic order
above 2 K, while BaEu2O4 has a quenched magnetic state. In order to study further the
magnetic properties of these compounds and to observe possible critical phenomena,
we report a preliminary μSR study on the BaGd2-xEuxO4 magnetic properties. No clear
muon spin precession is observed, meaning that static magnetic order may not be
observed. These preliminary results indicate a spin-glass behavior for x=0 and x=0.66
Eu concentration, due to a temperature dependent inverse linear behavior of the muon
relaxation rates. The possible nature of the magnetic order in these samples will be
discussed.
Reference:
[1] T. Besara et al., Progress in Solid State Chemistry 42, 23-36 (2014)
368
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Nature of the magnetic order of FeGa3-xGex intermetallic single
crystals
Julian Munevar1, Michael Cabrera-Baez2, Raquel A. Ribeiro2, Marcos A. Avila2,
Elvezio Morenzoni1
1
Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, Villigen,
Switzerland
2
Quantum Materials Group, Federal University of ABC, Santo André, Brazil
Recently, the FeGa3-xGex intermetallic compound has been reported to present a
very complex magnetic order due to hybridization of Ga(Ge) 4p and Fe 3d bands [1]
and a ferromagnetic quantum critical point (FMQCP) [1,2], among other properties.
However, little is known about the magnetic order that emerges at approximately
x=0.13 Ge concentration. We present ZF and LF muon spin rotation studies on single
crystals of intermetallic FeGa3-xGex from x=0.11 to x=0.43 Ge concentration. We
observe that all the ZF spectra obtained show a dip for short times followed by a tail,
which we fitted following a model describing a Gaussian broadened static magnetic
moment, in principle consistent with theoretical calculations and preliminary
Mössbauer spectroscopy measurements. Further discussion is given for the samples
close to the FMQCP, where the magnetic moment distribution can be described by a
Gaussian with center at zero, and a power law behavior is seen for the muon relaxation
rate of the x=0.11 sample. LF spectra show decoupling of the asymmetry in all the
samples, meaning static order for all the samples studied.
Reference:
[1] K. Umeo et al., PRB 86, 144421 (2012)
[2] M. Majumder et al., arXiv 1510.01974 (2015)
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Quantum Criticality in single crystalline YFe2Al10 determined from
zero-field and longitudinal-field μSR
C. Tan,1 K. Huang,1 Z.F. Ding,1 J. Zhang,1 D.E. MacLaughlin,2 O.O. Bernal,3 P.C. Ho,4 L.S.
Wu,5 M. Aronson,5, 6 and L. Shu1, 7
1
State Key Laboratory of Surface Physics, Department of Physics, Fudan University, Shanghai
200433, China
2
Department of Physics and Astronomy, University of California, Riverside, California 92521,
USA
3
Department of Physics and Astronomy, California State University, Los Angeles, California
90032, USA
4
Department of Physics, California State University Fresno, Fresno, California 93740, USA
5
Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794,
USA
6
Condensed Matter Physics and Materials Science Department,Brookhaven National
7
200433, China
Muon spin relaxation (µSR ) measurements were performed on single crystalline
YFe2Al10 down to 19 mK and in magnetic fields up to ∼100 Oe. Zero-field-µSR
measurements showed no evidence of magnetic order down to 19 mK, and finds that
the depolarization rate λ is temperature independent above 1 K but increases in an
exponential behavior for T< 1 K. Longitudinal-field µSR measurements reveals a
time-field scaling where G (t, H) = G (t = Hγ), with = 0.67. Comparison of YFe2Al10
to other ferromagnetic systems near a quantum critical point is discussed, further
evidence that YFe2Al10 is in close proximity to a ferromagnetic quantum critical point.
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Quantum multicriticality in Sr3Ru2O7
Dan Sun1, A. Rost2, R. Perry3, M. Brando1 and A. P. Mackenzie1;4
1
Max-Planck Institute for Chemical Physics of Solids, Noethnitzerstr. 40, Dresden, 01187,
Germany
2
Max-Planck Institute for Solid State Research, Heisenbergstra e 1, Stuttgart, 70569, Germany
3
University College London,Gower Street, London,WC1E 6BT, United Kingdom
4
Scottish Universities Physics Alliance,School of Physics and Astronomy,University of St.
Andrews, North Haugh,St. Andrews KY16 9SS, United Kingdom(Dated: January 15, 2016)
The low temperature phase diagram of the layered perovskite metal Sr3Ru2O7 is of
considerable interest because of the interplay between phase formation and quantum
criticality [1,2]. We have performed high resolution speci c heat and magnetocaloric
measurements down to temperatures as low as 65 mK, uncovering evidence that a
feature at 7.5 T previously thought to be a crossover is a quantum critical point
resulting from the suppression towards T=0 of an extremely low energy scale.
Additionally, we report for the rst time the observation of thermodynamic signatures
associated with the appearance of incommensurate magnetic order recently reported
in neutron scattering measurements [3].
Reference:
[1] S. Grigera, et al. Science 306, 1154 (2004)
[2] R. Borzi, et al. Science 315, 214 (2007)
[3] C. Lester, et al. Nature Materials 14, 373 (2015)
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Low-energy excitations of the spin-density-wave masked
ferromagnetic quantum critical point in Nb1-yFe2+y
Philipp G. Niklowitz1, James Poulten1, Maximilian Hirschberger2, William Duncan1, Andreas
Neubauer3, Petr Cermak4, Astrid Schneidewind4, Enrico Faulhaber4, Jean-Michel Mignot5, Klaus
Seemann4, Christian Pfleiderer3, F. Malte Grosche6
1
Department of Physics, Royal Holloway, University of London, Egham, TW20 0EX, U.K.
2
Department of Physics, Princeton University, NJ 08544, U.S.A.
3
Fakultät für Physik, Technische Universität München , 85748 Garching, Germany
4
Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), Technische Universität München,
85748 Garching, Germany
5
Laboratoire Léon Brillouin, CEA-CNRS, CEA/Saclay, 91191 Gif sur Yvette, France
6
Cavendish Laboratory, University of Cambridge, CB3 0HE, U.K.
Many experimental and theoretical studies suggest that it is difficult to approach
ferromagnetic quantum critical points in real materials. Instead, a variety of escape
routes have been observed, notably the occurrence of a first order transition or
superconductivity. The bulk properties of the C14 Laves phase Nb1-yFe2+y suggest a
third scenario: marginal Fermi liquid behaviour as expected of a ferromagnetic
quantum critical point (FM QCP) [1], but masking of the FM QCP itself by modulated
magnetic order.[2]
We have directly observed the ordering wavevector qSDW of this state and its B, T,
and y dependence by neutron diffraction on several single-crystalline samples,
showing that the FM QPC is masked by spin-density-wave (SDW) order.
Most recently, we have added to our results comprehensive inelastic neutron
scattering data, which reveals the existence of characteristic low-energy magnetic
excitations in this system. We have determined the q and T dependence of those
excitations in a range covering the paramagnetic (PM), SDW and FM state. The q
dependence of the quasielastic excitations in the PM state is characterised by multiple
minima in the linewidth. The inverse linewidth is found to diverge at the SDW-FM
phase transition. The peculiar q dependence of the quasielastic scattering at higher
temperatures is mirrored by a multiple-minima containing dispersion of damped
excitations in the FM state. The observed excitation pattern reflects the simultaneous
proximity of the Nb1-yFe2+y system to two types of magnetic order, which makes this
a candidate system for SDW order emerging from an FM QCP.
References:
[1] M. Brando et al., Phys. Rev. Lett. 101, 026401 (2008)
[2] D. Rauch et al., Phys. Rev. B 91, 174404 (2015)
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Tuning the quantum critical magnetism in ZrFe4Si2 by Ge and
Y substitution
K. Weber1,2, M. O. Ajeesh1, N. Mufti1, T. Goltz2, T. Woike3, C. Bergmann1, H.-H. Klauß2,
H. Rosner1, M. Nicklas1, C. Geibel1
1
2
Institute of Solid State Physics, TU Dresden, Germany
3
Institute for Structural Physics, TU Dresden, Germany
The intermetallic compound series AFe4X2 (A = Y, Lu, Zr; X = Si, Ge) presents a
rare case of magnetic frustrated metallic systems. In particular ZrFe4 Si2 is of strong
interest because our results indicate this system to be very close to a quantum critical
point where Fe magnetic order disappears. To get a deeper insight into its ground state,
we performed a detailed study of Ge and Y substituted ZrFe4Si2.
The isovalent substitution of Ge for Si induces a negative chemical pressure as Ge
is larger than Si. As expected from this, the substitution results in the formation of a
well-defined antiferromagnetic order with Néel temperatures increasing up to 25 K at
40 % of Ge. This confirms ZrFe4Si2 to be extremely close to the quantum critical
point, just on the magnetic side of it.
With the second substitution series YxZr1−xFe4Si2 we investigate the development
from the week antiferromagnetic order in ZrFe4Si2 towards the strange magnetism in
YFe4Si2, where we observe a two-step magnetic ordering at TN1 = 76 K andTN2 = 56 K.
Our results are discussed and compared with pressure measurements performed on
the AFe4X2systems.
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Magnetic order and valence change in the A-site ordered
perovskite Cr oxide CaCu3Cr4O12 probed by 63,65Cu NQR
Yoshiaki Kobayashi1, Daiki Koyanagi1, Masayuki Itoh1, Masahiko Isobe2, Hidenori
Takagi2, Hiroya Sakurai3
1
Department of Physics, Graduate School of Science, Nagoya University, Nagoya,
Japan
2
3
Environment and Energy Materials Division, National Institute for Materials Science,
Tsukuba, Japan
63,65
Cu-nuclear quadrupole resonance (NQR) measurements on the A-site ordered
perovskite Cr oxide CaCu3Cr4O12 have been carried out to investigate magnetic and
electronic properties of CaCu3Cr4O12. Although electrical resistivity and magnetic
susceptibility have no intelligible change in the entire temperature range between 2
and 300 K, we found that 63,65Cu-NQR frequency νNQR and the NQR spectral
widthΔνNQR increase at ~130 and ~50 K. The low-energy magnetic fluctuation
monitored by the 63,65Cu nuclear spin-lattice relaxation rates changes at ~130 and ~50
K. Thus we conclude a magnetic order takes place at ~130 K and a magnetic structural
change at ~50 K, accompanied by the Cu and Cr valence changes. We also discuss the
relationship between the valence states and the magnetic orders.
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Study on magnetic property of antiferromagnetic compound
Sr2VO3CoAs by NMR measurements
H. Ohta1, M. Imai2, D. Noguchi1, C. Michioka2, H. Aruga Katori1 and K. Yoshimura2,3
1Division of Advanced Applied Physics, Institute of Engineering, Tokyo University of
Agriculture and Technology, JAPAN
2Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502,
Japan 3Research Center for Low Temperature and Materials Sciences, Kyoto University, Kyoto
606-8501,
Japan
We studied magnetic property of an antiferromagnetic compound Sr2VO3CoAs
with conducting CoAs layers from a microscopic point of view by 75As- and 59CoNMR measurements. As a result of 75As-NMR measurements, we observed
anomalous shift of the center line in spectra and diverging tendency in spin-lattice
relaxation rate at antiferromagnetic transition temperature TN = 140 K. On the other
hand, spectra of 59Co-NMR did not show any anomaly around TN and they became
more broadening with decreasing T in the T region below 100 K. From these results,
we concluded that in the antiferromagnetic phase not magnetic moments of Co but
those of V are ordering. We also concluded that we successfully detected
magnetization of Co, which shows a nearly ferromagnetic behavior.
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Itinerant electronic ferromagnetism in novel layered compound
Sr3Sc2O5Co2As2 with body centered crystal structure
A. Suzuki1, H. Ohta1, H. Aruga. Katori1
1
Department of Applied Physics, Graduate School of Engineering, Tokyo University
of Agriculture and Technology, Tokyo, Japan
We synthesized polycrystalline samples of Sr3Sc2O5Co2As2, a new member of
compounds with CoAs conducting layers, and studied magnetism of this compound
by magnetic and electric resistivity measurements. As a result, Sr3Sc2O5Co2As2 was
revealed to be the first itinerant electronic ferromagnet with the space group of
I4/mmm among the compounds with CoAs layers. The Curie temperature is
determined as TC=41 K. From Arrott plots and M4-H/M plots, we estimated spin
fluctuation parameters within Takahashi’s theory of itinerant electronic magnetism.
Spin fluctuations of Sr3Sc2O5Co2As2 have a three-dimensional character and are
similar to those of other itinerant electronic ferromagnets with CoAs layers.
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Charge-spin-orbital state and strong ferromagnetism in the high
valence perovskite Sr(Fe0.5Ni0.5)O3
Fengren Fan, Hua Wu
Department of Physics, Fudan University, Shanghai, China
Progressing, for details see poster.
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Fermi Surface and Magnetic Properties in Ferromagnet CoS2 and
Paramagnet CoSe2 with the Pyrite-type Cubic Structure
Atsushi Teruya1, Fuminori Suzuki1, Dai Aoki2, Fuminori Honda2, Ai Nakamura2,Hisatomo
Harima3, Kiyoharu Uchima4, Masato Hedo5, Takao Nakama5, and Yoshichika Ōnuki5
1
Graduate School of Engineering and Science, University of the Ryukyus, Nishihara,
2
Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313,
Japan 3Graduate School of Science, Kobe University, Kobe 657-8501, Japan
4
General Education, Okinawa Christian Junior College, Nishihara, Okinawa 903-0207,
Japan
5
Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan
We studied Co-based compounds such as a paramagnet CoGa3 [1], a
superconductor Zr2Co [2], a nearly ferromagnet SrCo2P2 [3], and a ferromagnet
LaCo2P2 [4] from viewpoints of Fermiology and magnetism. We continued these
studies for another compounds of CoSe2 and CoS2.
In the present study, we succeeded in growing high-quality single crystals of pyritetype cubic compounds CoSe2 and CoS2 using a transport agent of CoBr2, and
measured the electrical resistivity, specific heat, magnetic susceptibility,
magnetization, and the de Haas-van Alphen (dHvA) effect. We confirmed that CoSe2
is a paramagnet revealing a broad maximum around 50 K in the temperature
dependence of the magnetic susceptibility. The electronic specific heat coefficient is
moderately large, γ = 18 mJ/(K2·mol). On the other hand, CoS2 is a ferromagnet with
a Curie temperature TC = 122 K and an ordered moment μs = 0.90 μB/Co. The γ value
of 21 mJ/(K2·mol) in CoS2 is slightly larger than that of CoSe2. A large ordered
moment, together with a large γ value, is characteristic in CoS2. Correspondingly, we
detected a main dHvA branch with a large cyclotron effective mass of 13m0 in the
dHvA experiment. This is the largest cyclotron mass in the 3d-electron systems. The
detected dHvA branches in CoS2 and CoSe2 are discussed on the basis of the results
of energy band calculations, revealing a broken four-fold-symmetry in the angular
dependence of the dHvA frequency, reflecting the characteristic pyrite-type cubic
crystal structure.
References:
[1]A. Teruya et al., J. Phys. Soc. Jpn. 84, 054703 (2015).
[2]A. Teruya et al., printed in J. Phys. Soc. Jpn.
[3]A. Teruya et al., J. Phys. Soc. Jpn. 83, 113702 (2014).
[4]A. Teruya et al., Physics Procedia 75, 876 (2015).
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Magnetic properties of single crystalline HoTe3
M.S. Song1, B. Y. Kang1, K. K. Cho1B. K. Cho1*
1
School of Materials Science and Engineering, Gwangju Institute of Science and Technology
(GIST), Gwangju 61005, Korea
Charge density waves (CDWs) are in a broken ground state, driven by electronic
instabilities in a low-dimensional system with a highly anisotropic electronic structure
[1]. As one of the CDW materials, the RTe3 (R = rare earth elements) compound is a
quasi-two-dimensional system that consists of alternate layer stacking with two Te
layers and one RTe layer. Due to its easily tunable properties by either chemical
pressure or the application of pressure, RTe3 was recently researched to investigate
the energy gap in CDWs,the order of multiple CDWs and superconductivity under
pressure. Even though the magnetic properties of RTe3 in light rare earth elements
have been reported [2], magnetic and electronic information in heavy rare earth
elements remains unknown. In this study, the magnetic properties of HoTe3 were
investigated and two ferromagnetic transitions were discovered along a direction
perpendicular to the stacking axis while RTe3 with light rare earth elements showed
simple anti ferromagentism [2]. A single crystal, HoTe3, was grown by the self-flux
method. The crystal structure of HoTe3 was found to be weakly orthorombic (space
group Cmcm) and the lattice parameters were refined to be a = 4.2360 Å, b = 25.3387
Å, and c = 4.3554 Å from the powder XRD pattern using the Le Bail method. An
antiferromagnetic transition temperature was found at TN = 4.5 K for H // b and two
ferromagnetic transitions were found at Tc1= 3.5 K and Tc2= 4.5 K for H⊥b, as shown
in Fig. 1. We will discuss the nature of HoTe3 in detail.
Reference:
[1] G. Gruner, Density Waves in Solids _Perseus, Cambridge, MA, (1994.)
[2] Yuji Iyeiri, Teppei Okumura, Chishiro Michioka, and Kazuya Suzuki, Physical
Review B 67 144417 (2003)
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Structural, magnetic and magnetotransport studies on
Mn2NiGa Heusler alloys: Effect of different annealing
condition
Megha Vagadia1, K.R. Priolkar2 and A.K. Nigam1
1
Department of Condensed Matter Physics & Materials Science, Tata Institute of
Fundamental Research, Mumbai – 400005, India
2
Department of Physics, Goa University, Tailegao-Plateau, Goa – 403 206, India
We have studied the effect of different annealing conditions on structural, magnetic
and magnetotransport properties of Mn2NiGa Heusler alloys. The arc melted ingots of
Mn2NiGa were annealed at 1073K in an evacuated quartz tube for 48 hours and
subsequently subjected to different annealing conditions as follows: (1) furnace
cooling (FC) (2) controlled furnace cooling with rate of 5°C/min (SC) (3) quenched
in ice-water mixture and (I-W) (4) quenched in liquid N2 (N2). Le Bail fit of room
temperature X-ray diffraction patterns suggests co-existence of cubic L21 and 7M
monoclinic modulated structure. Temperature and magnetic field dependent
magnetization measurements demonstrate the strong influence of annealing condition
on structural phase transition temperatures, Curie temperature and saturation
magnetization. Magnetoresistance (MR) measurement as a function of applied
magnetic field shows asymmetry in MR about the direction of magnetic field in all
the samples under study.
380
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High Magnetic Field Visualization of Antiferromagnetic Phase
Dynamics
Zhigao Sheng1, Qingyou Lu1,2, Haibiao Zhou2, Qiyuan Feng2, Xueli Xu1, Long Cheng1,
M. Nakamura3, M. Kawasaki3. Y. Tokura3
1
High Magnetic Field Laboratory and Hefei Science Center, Chinese Academy of Science (CAS),
Hefei 230031, China
2
University of Science and Technology of China, Hefei 230031, P. R. China
3
RIKEN Center for Emergent Matter Science (CEMS), Wako 251-0198, Japan
Antiferromagnetism is of great technological importance as they are responsible for
the exchange-bias effect that is widely used in state-of-the-art magnetic storage
devices. The visualization of antiferromagnetic phase, especially it’s birth and death
from magnetic disorder phase, is barely reported due to the experimental difficulties
on detecting nearly zero magnetic moment. In this report, we will demonstrate a
microscopic visualization of antieferromagnetism in a charge/orbit ordered manganite
thin film by means of high field magnetic force microscope. In such thin film with
artificial strain, the dynamics of antiferromagnetic phase domains show crystal -like
behavior, which is quite different from other magnetic phase observed before. The
relaxation and re-entrance behavior, which related to the competition between internal
freedom degree and external field, are also presented through images. These
experiments provide a microscopic basis for descriptions and application of
antiferromagnetism in provskite transition metal oxides.
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Exploring the magnetic phases in the highly anisotropic
ferromagnet CeRu2Ga2B by magnetic force microscopy
Dirk Wulferding1, Ilkyu Yang1, Hoon Kim1,2, Roman Movshovich3, Ryan Baumbach4 , Eric
Bauer3, Leonardo Civale3, Han Woong Yeom1,2, Jeehoon Kim1,2
1
CALDES, Institute for Basic Science, Pohang, Korea
2
3
Department of Physics, POSTECH, Pohang, Korea
MPA-CMMS, Los Alamos Natl. Lab., Los Alamos, USA
4
NHML, Florida State Univ., Tallahassee, USA
The interplay of spin and orbital degrees of freedom in strongly correlated electron
systems is a fruitful source of many exotic and unexpected phenomena. In particular,
rich magnetic phase diagrams can be found in systems with additional magnetic
anisotropies. While the bulk magnetic properties are often well explored, the evolution
of the microscopic magnetic domain structure within the phase diagram remains
elusive. Using low temperature magnetic force microscopy with vector magnet
capabilities, we explore the evolution and manipulation of magnetic domains in the
centrosymmetric ferromagnet CeRu2Ga2B [1]. This compound exhibits transitions
among dendritic, stripe, and bubble domain phases. We highlight the domain
evolution with a vector magnetic field in this Ising-like spin system.
References:
[1] R. Baumbach, et al., J. Phys.: Condens. Matter 24, 185702 (2012).
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Tunnel Diode Oscillator measurement using diamond anvil cells in
a
dilution fridge
King Yau Yip1, Q. Niu1, S. K. Goh1
1
Department of Physics, The Chinese University of Hong Kong, Sha Tin, New Territories,
Hong Kong, China
The combination of high pressure, high magnetic field and low temperature is
useful for the studies of strongly correlated electron systems. To study small single
crystals under such extreme conditions, we developed a tunnel diode oscillator based
contactless measurement technique for our anvil cells and dilution fridge. We will
describe the details of the set-up and present some data obtained on tiny single crystals
to demonstrate the feasibility of extracting useful information. The future prospect of
the set-up will also be discussed.
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Study of the strongly correlated electron systems by neutrons at
Hans Maier-Leibnitz Zentrum (MLZ), Garching, Germany
Petr Čermák1, Sultan Demirdiş1, Robert Georgii2,3, Thomas Keller4,5, Kirill Nemkovski1, Jitae
T. Park2, Astrid Schneidewind1, Oleg Sobolev2,6, Yixi Su1
1
Jülich Center for Neutron Science at MLZ, Forschungszentrum Jülich, Garching,
DE 2Heinz Maier-Leibnitz Zentrum, Technische Universität München, Garching,
DE 3Physik-Department E21, Technische Universität München, Garching, DE
4
Max-Planck-Institut für Festkörperforschung, Stuttgart, DE
5
Max Planck Society Outstation at the Heinz Maier-Leibnitz Zentrum (MLZ), Garching,
DE 6Institute for Physical Chemistry, Georg-August-University, Göttingen, DE
Neutron scattering is the leading technique for
measuring magnetic correlations in solids. It can be
used as a direct probe for studying magnetic order
and magnetic moment coupling in frustrated or low
dimensional materials. It can also prove dynamic
correlations, their lifetime and diffuse scattering in the absence of magnetic order. The
suite of neutron spectroscopy instruments at the MLZ, located at the research reactor
FRM II in Garching, provides a unique opportunity to study emerging as well as wellknown strongly correlated electron materials. The MLZ provides free beam time for
scientific use at its instruments for everybody (according to the decision of the review
panel and under the condition of publishing the results).
In this poster presentation, we will introduce:
 the diffuse scattering neutron time of flight spectrometer with
polarizationanalysis DNS,
 the universal cold three axis spectrometer/diffractometer MIRA,
 the three axis spectrometers PANDA (cold) and PUMA (thermal)
 and the spin echo three axis spectrometer TRISP.
Our recent highlights cover broad variety of scientific fields like frustrated magnetism
(e.g. bilayer pervoskite Sr3Fe2O7 [1] or lifetime of spin waves in 2D and 3D systems
[2]), magnetic excitations in insulators (e.g. in cobalt oxides [3]), quantum phase
transitions (e.g. absolute zero vibrations in superfluid helium [4] or Higgs mechanism
in quantum spin ice [5]), superconductivity (e.g. nematic correlations in high
temperature superconductors [6]) or novel magnetic states (e.g. helimagnons,
skyrmions [7,8]). You are welcomed to visit our poster stand and ask for details
orintroduction to our proposal review system.
References:
[1] Phys. Rev. Lett. 113, 147206 (2014)
992(2012)
[2] Phys. Rev. Lett. 111, 017204 (2013)
[3] Nature Comm. 5, 5731 (2014)
[4] Phys. Rev. Lett. 109, 155305 (2012)
(2015)
384
[5] Nature Communication 3:
[6] Science 345, 657 (2014)
[7] Nature Materials 14, 478–483 (2015)
[8] Phys. Rev. Letter 115, 097203
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Three-Axis Low Energy Neutron Spectroscopy at Institut LaueLangevin
M. Klicpera1,2, Martin BOEHM1, Stephane ROUX1, Jiri KULDA1, Vladimir SECHOVSKY2,
Pavel SVOBODA2, Jan SAROUN3, Paul STEFFENS1
1
2
Institut Laue-Langevin, 38042 Grenoble Cedex 9, France
Charles University in Prague, Faculty of Mathematics and Physics, Department of Condensed
Matter Physics, Ke Karlovu 5, 121 16 Prague 2, Czech Republic
3
Nuclear Physics Institute AS CR, 25068 Rez, Czech Republic
Neutron inelastic scattering studies using three-axis spectrometers (TAS) are
indispensable for measuring elementary excitations of magnetic correlated systems.
Neutron inelastic scattering remains the method yielding the most complete
information on the role of space and time correlations and their interplay in the behavior
of condensed matter systems. Moreover, neutrons couple with comparable strength to
both the structural and magnetic degrees of freedom and the two scatteringcomponents
can be quite cleanly separated using polarized neutron techniques.
The new cold neutron spectrometer ThALES at the Institut Laue-Langevin has been
optimized for exploring correlated magnetic systems beyond the experimental
possibilities of its predecessor IN14 spectrometer [1-3] in terms of data collection rate,
kinematical range and neutron polarization analysis. ThALES covers momentum
transfers up to 2 Å-1and energy transfers up to 18 meV with enhanced energy resolution
(~0.05 meV at incident wavenumber ki = 1.5 Å-1). The modified spectrometer
shielding can host high field measurements up to 15 T in the complete dynamical range,
while the new Heusler monochromator will provide a polarized neutron flux
comparable to the old IN14 in its unpolarized mode. The challenge of measuring
magnetic excitations in mm3-sized samples has been addressed by combining the
virtual source concept with a focusing guide and a Si 111 focusing monochromator.
We present first results demonstrating the capabilities of thisspectrometer for
measuring magnetic correlated systems. The commissioning phase of ThALES has
been finished in 2015. The instrument is now available to the user community. The
ThALES project is a collaboration between ILL and Charles University in Prague,
financed by the Czech Ministry of Science and Education (Project no. LM2010001).
Reference:
[1] Boehm M., Roux S., Hiess A., Kulda J., JMMM 310 (2007), e965-e967.
[2] Boehm M., Roux S., Hiess A., Kulda J., I. Saroun, Meas. Sci. Technol 19
(2008), p.034024.
[3] Boehm M., Cermak P., Kulda J., Hiess A., Steffens P., Šaroun J., J. Phys. Soc. Jap.
2, Supplement A, SA026 (2013).
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Detection of a Pair Density Wave in Bi2Sr2CaCu2O8 using Scanned
Josephson Tunneling
S.D. Edkins1,2, M. H. Hamidian1,3, Sang Hyun Joo4, A. Kostin1, H. Eisaki5, S. Uchida5, M. J .
Lawler1,6, E.-A. Kim1, A. P. Mackenzie2,7, K. Fujita1,8, Jinho Lee5 and J. C. Davis1,2,8,9
1
LASSP, Department of Physics, Cornell University, Ithaca, NY 14853, USA
School of Physics and Astron., University of St. Andrews, Fife KY16 9SS, Scotland.
3
Department of Physics, Harvard University, Cambridge, MA 02138, USA
4
Department of Physics and Astron., Seoul National University, Seoul 151-747, Korea.
5
Inst. of Advanced Industrial Science and Tech., Tsukuba, Ibaraki 305-8568, Japan.
6
Department of Physics, Binghamton University, Binghamton, NY 13902-6000, USA
7
Max-Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany.
8
CMPMS Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
9
Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY 14853, USA.
2
The quantum condensate of Cooper-pairs forming a superconductor was originally
conceived to be translationally invariant. In theory, however, pairs can exist with finite
momentum Q and thereby generate states with spatially modulating Cooper-pair
density [1,2]. While never directly observed in any superconductor, such a state has
been created in ultra-cold 6Li gas [3]. It is now widely hypothesized that the cuprate
pseudogap phase contains such a ‘pair density wave’ (PDW) state.
Here we use scanned Josephson tunneling microscopy (SJTM) to image Cooperpair tunneling from a d-wave superconducting STM tip at millikelvin temperatures to
the Cooper-pair condensate of Bi2Sr2CaCu2O8 .The resulting images of the Cooperpair condensate show clear pair density modulations oriented along the Cu-O bond
directions. Fourier analysis reveals the direct signature of a Cooper-pair density wave
at wavevectors QP≈(0.25,0)2π/a0;(0,0.25)2π/a0; the amplitude of these modulations is
~ 5% of the homogeneous condensate density and their form factor exhibits primarily
s/s’-symmetry[4]. We review the implications from the discovery of a PDW state, and
the observed interplay of CDW, PDW and dSC, for the microscopic theory of the
cuprate pseudogap phase.
Reference:
[1] P. Fulde and R.A. Ferrell, Phys. Rev. 135: A550 (1964 ).
[2] A.I. Larkin, Yu.N. Ovchinnikov, Sov. Phys. JETP 20, 762 (1965).
[3] Y. Liao et al, Nature 467, 567 (2010).
[4] M. Hamidian * & S. D .Edkins* et al. arXiv:1511.08124 (2016).
386
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High magnetic field study of the vortex lattice structure in YBa2Cu3O7
R. Riyat,1 A. S. Cameron,1,2 A. T. Holmes,1 E. Blackburn,1 E. M. Forgan,1 O. Prokhnenko3 W-D.
Stein,3 M. Bartkowiak,3 and A. Erb4
1
School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT,
UK
2
Institut fϋr Festkorperphysik, Helmholtzstraße 10, 01069 Dresden, Germany
3
Helmholtz Zentrum Berlin, Wannsee, Berlin, Germany
4
Walther Meissner Institut, BAdW, D-85784, Garching, Germany
Small-angle neutron scattering (SANS) measurements of the vortex lattice structure
as a function of field and temperature make it possible to extract information such as
the penetration depth, coherence length and the superconducting gap structure of a
given superconductor. In YBa2Cu3O7 (YBCO) SANS can reveal the effective mass
anisotropy, the vortex lattice melting, the vortex lattice pinning [1] and the fieldinduced non-locality [2].
The vortex lattice in YBCO has previously been studied up to 17 T by SANS [1].
We present a SANS study on the vortex lattice structure in detwinned YBCO up to 25
T carried out on the EXED instrument at HZB (Helmholtz Zentrum Berlin). The vortex
lattice in YBCO undergoes several structural transitions with the application of
magnetic field. A low-field transition occurs initially whereby the hexagonal vortex
lattice undergoes a 90 degree reorientation. At higher fields (10 T) the vortex lattice
undergoes a second transition whereby the structure changes from hexagonal to
rhombic. The opening angle of this rhombic vortex lattice appears to continually
increase with magnetic field up to 17 T (passing through square at approximately 13
T). However, now that we have access to magnetic fields up to 25 T, we appear to have
observed the high field limit of the vortex lattice structure in YBCO whereby the
opening angle stops varying with the application of field. We also present results on
the variation of the vortex lattice form factor up to 25 T at low temperatures.
Reference:
[1] A. S. Cameron, J. S. White, A. T. Holmes, E. Blackburn, E. M. Forgan, R. Riyat,
T. Loew, C. D.Dewhurst, and A. Erb. Phys. Rev. B 90, 054501 (2014)
[2] J. S. White, R. W. Heslop, A. T. Holmes, E. M. Forgan, V. Hinkov, N.
Egetenmeyer, J. L. Gavilano, M. Laver, C. D. Dewhurst, R. Cubitt, and A.
Erb. Phys. Rev. B 84, 104519 (2011)
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A modified cRPA method incorporating non-local screening process
Hirofumi Sakakibara1*, Seung Woo Jang2, Hiori Kino3, Myung Joon Han3, Kazuhiko Kuroki4,
and Takao Kotani1
1Ddepartment of Applied Mathematics and Physics, Tottori University, Tottori, Japan
2 Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon,
Korea
3National Institute for material science (NIMS), Tsukuba, Japan
4Department of Physics, Osaka University, Toyonaka, Osaka, Japan
In order to predict material properties such as superconducting critical temperatures based on the
first-principles calculations, we have to go through a model Hamiltonian. That is, we have to
determine parameters in the Hamiltonian, especially the effective interaction U. For this purpose,
we may use the constrained random phase approximation (cRPA) [1,2,3], which is the RPA method
excluding the screening effects in the model space. However, cRPA method gives slow attenuation
of Coulomb potential, which is approximately proportional to 1/r. This is because that we exclude
the metallic screening in conventional cRPA scheme. Although the effect of long-range interaction
is sometimes explicitly treated [4], however, we usually need a model consisting of short-range
interaction in order to perform high-accuracy model calculation. Schüler et al. gives a formalism
for down-folding of long-range interaction into the onsite U [4].
Here we present a new simple down-folding approach, named “model-projected RPA (mRPA)”,
to appropriately truncate the long-range part of U in the combination of the first-principles and
model calculations. After we determine the dimension of model space and one-body part of model
Hamiltonian via the Wannier function method, we evaluate the onsite UM so as to satisfy the relation
WD =1/(1- UMPM ) UM, where PM is the Lindhard polarization function for the model; WD is given
by the first-principles method. In the presentation, we show results for the single band model of
Hg2BaCuO4, where we compare values for mRPA and cRPA based on LDA and QSGW method
[6].
Reference:
[1] T. Kotani, J. Phys.: Condens. Matter 12, 2413 (2000).
[2] F. Aryasetiawan et al., Phys. Rev. B 70, 195104 (2004).
[3] E. Şaşıoğlu, et al., Phys. Rev. B 83, 121101(R) (2011).
[4] P. Hansmann, Phys. Rev. Lett. 110, 166401 (2013)
[5] M. Schüler et al., Phys. Rev. Lett. 111, 036601 (2013).
[6] T. Kotani, J. Phys. Soc. Jpn. 83, 094711 (2014).
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Electron-doping effect on the spin excitation spectrum in
Pr1.4-xLa0.6CexCuO4+δ
S. Asano1, K. Tsutumi1, K. Sato1, and M. Fjita2
1Department of Physics, Tohoku University, Sendai, Japan
2Institute for Materials Research, Tohoku University, Sendai, Japan
The high-transition-temperature superconductivity in cuprate oxide emerges, when
the sufficient number of carriers is introduced in the antiferromagnetically ordered Mott
insulator. To understand the mechanism of superconductivity, the study of electronhole symmetry in the physical properties is quite important, since it can be a crucial test
of theoretical models. In the hole-doped system, the doping evolution of spin
excitations has been extensively studied by neutron scattering measurement. It was
clarified that he hourglass-shaped excitation, which consists of an inwardly dispersive
low-energy excitation and a spin-wave-like high-energy excitation, is commonly
observed in the superconducting phase [1]. Appearance of hourglass excitation in the
SC phase suggests the close connection between a characteristic spin correlations and
the superconductivity. On the other hand, the experimental study of spin excitation in
the electron-doped system is quite limited, mainly due to the difficulties in the
preparation of high quality crystal. Although the existence of high-energy spin
excitation was confirmed in the optimally-doped sample [2], the details in the
dynamical structure factor in a wide energy and momentum spaces is unclear. In
particular, both Ce-substitution and oxygen-reduction annealing procedure known to
be essential to the emergence of superconductivity in the electron-doped 214-system,
however, their effect on the magnetism is still controversial.
In order to gain insight into the effect of electron-doping which is brought through
the Ce-substitution on the spin excitation, we performed high-energy inelastic neutron
scattering measurements on the as-grown Pr1.4-xLa0.6CexCuO4+δ (x = 0, 0.08) with using
the chopper spectrometer 4SEASONS installed in Japan Proton Accelerator Research
Complex (J-PARC). We succeeded in observing the spin excitation up to ~300 meV in
both parent and electron-doped samples. The spin excitations in the x = 0 sample is well
described by spin-wave excitation for S=1/2 two-dimensional Heisenberg model with
the nearest neighbor exchange constant J~140 meV. In the x = 0.08 sample, we found
that the spectral weight around 300 meV,which is comparable to the magnetic zone
boundary energy in x = 0, persists at the zone center of (0.5, 0.5) reciprocal position.
These results suggest the elongation of spin excitation by the electron-doping,
contrastive to the negligible doping effect on the high-energy spin excitation in the
hole-doped system. Thus, there is the electron-hole asymmetry in the shape of entire
spin excitation against doping.
Reference:
[1] S. M. Hayden et al., Nature. 429. 531. (2004)
M. Tranquada et al., Nature. 429. 534. (2004)
[2] M. Fujita et al., JPSJ 75, 093704 (2006).
D. Wilson et al., Phys. Rev. Lett. 96, 157001 (2006)
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Oxygen and copper isotope effects on the pseudogap formation
temperature in underdoped to overdoped cuprates: Pseudogap
induced by pairing correlations above Tc in cuprates with large and
small Fermi surfaces
Khudayberdiev Z.S. Dzhumanov S1.
1
institute of Nuclear Physics, Uzbek Academy of Sciences, Ulugbek, Tashkent, 100214, Uzbekistan
We investigate the pseudogap (PG) state and the peculiar oxygen and copper isotope
effects on the PG onset temperature T* in cuprate superconductors with large and small
Fermi surfaces within the polaron model and two different 5CS-based approaches
extended to the intermediate coupling regime. We argue that the unconventional
electron-phonon interactions are responsible for the polaron formation and BCS-like
pairing correlations above Tc in underdoped to overdoped cuprates, which are exotic
(non-BCS) superconductors. Using the generalized BCS-like theory, we calculate
pseudogap formation temperatures T*, isotope shifts ΔT*，oxygen and copper isotope
exponents (i.e. 𝛼 𝑇𝑂∗ and 𝛼 𝑇𝐶𝑢∗ ) and show that isotope effects on T* strongly depend on
strengths of Coulomb and electron-phonon interactions, doping levels and dielectric
constants of the cuprates. This theory explains the existence of small positive or sign
reversed oxygen isotope effect, sizable and very large negative oxygen and copper
isotope effects on T* in cuprates with large Fermi surfaces. Further, we use another
version of the extended BCS-like model to study the PG formation and the peculiar
isotope effects on T* in deeply underdoped cuprates with small Fermi surfaces and
predict the existence of small and sizable negative oxygen and copper isotope effects
on T* in such underdoped cuprates. The results for T*, isotope shifts ΔT* and
exponents (𝛼 𝑇𝑂∗ and 𝛼 𝑇𝐶𝑢∗ ) in different classes of high-Tc cuprates are in good agreement
with the existing well-established experimental data and explain the controversy
between various experiments on isotope effects for T* in the cuprates.
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High-Tc superconductivity in the bilayer model: Beyond the
renormalized mean-field theory
M. Zegrodnik1 J. Spałek2,1
1
Academic Centre for Materials and Nanotechnology, AGH University of Science
and Technology, Al. Mickiewicza 30, 30-059 Krakow, Poland
2
Intitute of Physics, Jagiellonian University, Lojasiewicza 11, 30-348 Krakow, Poland
The full Guztzwiller wave function solution of the so-called t-J-U-V model is
analyzed for the case of the bilayer square lattice. The zeroth order solution coming out
from the proper diagrammatic expansion of the Gutzwiller wave function [1]
reproduces the results of the renormalized mean-field theory (RMFT) amended with
the so-called statistical consistency conditions [2]. The model analyzed by us refers to
the copper-based superconductors with two Cu-O layers in the unit cell, with the
interplanar coupling of the exchange or Coulomb types. The stability of the d-wave
superconducting phase is analyzed as function of both the doping and the interplanar
couplings. For the sake of comparison, the situation with the single particle interplanar
hopping is also considered. Former results for a single-plane situation are fully
recovered when the interplanar coupling is neglected [3].
The work has been supported by the National Science Center (NCN) under the grant
MAESTRO, No. DEC-2012/04/A/ST3/00342.
Reference:
[1] J. Jędrak and J. Spałek, Phys. Rev. B 83, 104512 (2011).
[2] J. Kaczmarczyk et al., Phys. Rev. B 88, 115127 (2013); J. Kaczmarczyk, J.
Bünemann, and J. Spałek, New J. Phys. 16, 073018 (2014).
[3] J. Spałek and M. Zegrodnik, unpublished.
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Unconventional Superconductivity in Molecular Conductors:
Importance of Intradimer Charge Degrees of Freedom
Hiroshi Watanabe1, Hitoshi Seo2,3, and Seiji Yunoki4,5
1
Waseda Institute for Advanced Study, Waseda University, Tokyo, Japan
2
Condensed Matter Theory Laboratory, RIKEN, Saitama, Japan
3
Quantum Matter Theory Research Team, RIKEN CEMS, Saitama, Japan
4
Computational Quantum Matter Research Team, RIKEN CEMS, Saitama, Japan
5
Computational Materials Science Research Team, RIKEN AICS, Hyogo, Japan
The family of quasi two-dimensional molecular conductors, -(BEDT-TTF)2X, has
extensively been studied as a typical example of strongly correlated electron system.
Due to the strong hybridization, two BEDT-TTF molecules facing each other can be
regarded as a dimer and form an anisotropic triangular lattice with one hole per dimer
(half-filled system). Depending on the monovalent anion X, they show various quantum
phases such as antiferromagnetic (AF) and spin-liquid dimer-Mott insulators, and
superconductivity (SC). Although the effective half-filled dimer model well describes
the Mott physics [1], recent experimental and theoretical studies suggest the importance
of intradimer charge degrees of freedom which are neglected in the dimer model. The
intradimer charge degrees of freedom lead to charge fluctuations within the dimers and
should affect the electronic structure and mechanisms of emergent phenomena.
Here, we theoretically study the phase competition in -(BEDT-TTF)2X by taking
account the intradimer charge degrees of freedom. We consider a quarter-filled (hole)
four-band extended Hubbard model including onsite (U) and intersite Coulomb
interactions with -type geometry. The ground state properties are studied with the
variational Monte Carlo method. In the ground state phase diagram of the model
parameters for X=Cu[N(CN)2]Br, we find the SC state near the border between the
dimer-Mott and charge-ordered states. The extended s (or s+-)-wave symmetry is
favored and the gap function changes its sign depending on the band [2, 3]. Without the
intersite Coulomb interactions, SC is difficult to arise since not only the spin fluctuation
but also the charge fluctuation is important for the stability of SC. Our result supports
the importance of intradimer charge degrees of freedom and leads to a unified view of
-(BEDT-TTF)2X.
Reference:
[1] K. Kanoda and R. Kato, Annu. Rev. Condens. Matter Phys. 2011. 2, 167 (2011)
[2] K. Kuroki et al., Phys. Rev. B 65, 100516(R) (2002).
[3] A. Sekine, J. Nasu, and S. Ishihara, Phys. Rev. B 87, 085133 (2013).
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Electrical transport properties of the unconventional superconductor
YFe2Ge2
K. Semeniuk1, J. Chen1, Z. Feng2, P. Brown1, Y. Zou1, G. Lampronti3, and M. Grosche1
1
2
Cavendish Laboratory, University of Cambridge, Cambridge UK
London Centre of Nanotechnology, University College London, London UK
3
Dept. of Earth Sciences, University of Cambridge, Cambridge UK
YFe2Ge2 is a paramagnetic d-electron system which stands out due to the high
Sommerfeld ratio of its specific heat capacity of 100 mJ/(mol K2) and non Fermi-liquid
T3/2power law temperature dependence of the electrical resistivity. The material
wasfound to be superconducting below about 1.8 K [1].
Advances in YFe2Ge2 crystal growth allowed us to obtain high quality samples
with residual resistivity ratios of the order of 200. Recent measurements of
magnetisation and heat capacity provide further evidence for superconductivity, and
the correlation between the transition temperature and the sample quality, theenhanced
Sommerfeld coefficient and the anomalous T-dependence of the resistivity indicate
that superconductivity in YFe2Ge2 is unconventional [2]. We report the results of
detailed electrical resistivity measurements on YFe2Ge2 as a function of temperature,
magnetic field and hydrostatic pressure, which provide further insight into the nature
of superconducting and normal states of the material.
References:
[1] Y. Zou et al, Physica Status Solidi (RRL) 8, 928 (2014).
[2] J. Chen et al, arXiv:1507.01436v2
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Crystal growth of YFe2Ge2 and the dependence of its
superconducting properties on sample preparation
Jiasheng Chen1, Konstantin Semeniuk1, Philip Brown1, Giulio I. Lampronti2, and F.
Malte Grosche1
1
Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
2
Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United
Kingdom
The intermetallic d-electron system YFe2Ge2 exhibits an unusually high Sommerfeld
ratio of specific heat capacity of C/T ~ 100 mJ/(molK2), signaling strong electronic
correlations. Evidence of superconductivity has been reported in polycrystals and in fluxgrown single crystals [1] with residual resistance ratios (RRR) of the order of 50, but these
samples show no thermodynamic signatures of a bulk superconducting transition. We find
that by combining (i) a pre-reaction of YFe2, (ii) careful control of nominal composition,
and (iii) subsequent annealing procedures, the polycrystalline YFe2Ge2 samples grown
using a radio-frequency (RF) induction furnace can reach RRR values ~ 200 with resistive
superconducting transitions at temperatures of around 1.85K. This new generation of
sample displays clear heat capacity anomalies as well as nearly 100% diamagnetic
screening, confirming the bulk nature of superconductivity in YFe2Ge2. [2]. We present
details of the sample preparation and characterization and discuss the correlation between
composition, annealing protocol and superconductivity.
Reference:
[1] Y. Zou et al., Physica Status Solidi - Rapid Research Letters 8, 928 (2014), H.
Kim et al., Philos Mag, 95, 804 (2015).
[2] J. Chen et al., arXiv:1507.01436v2 (2015).
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Search for unconventional superconductors among YT2M2
compounds (T = d-electron transition metal, M = Si or Ge)
A. P. Pikul1, G. Chajewsk1, P. Wiśniewski1, M. Samsel–Czekała1, D. Kaczorowski1
1
Institute of Low Temperature and Structure Research, Polish Academy of Sciences,
Wrocław, Poland
Motivated by the recent discovery of unconventional superconductivity in
YFe2 Ge2 [1], we have undertaken systematic reinvestigation of the formation and the
physical properties of yttrium-based 1:2:2 silicides and germanides. In this contribution
we report on the syntheses and the crystal structures of several YT2M2 compounds (T
= d-electron transition metal, and M = Si or Ge) as well as on their low-temperature
physical properties. The experimental data are supplemented by the results of band
structure calculations. Most of the representatives of the series crystallize in the
tetragonal ThCr2Si2-type structure (space group I4/mmm), while only very few of them
form with the tetragonal CaBe2Ge2-type structure (space group P4/nmm). Whereas the
former materials possess three-dimensional Fermi surface sheets, the later ones exhibit
numerous quasi-two-dimensional Fermi surface sheets. Remarkably, superconductivity
in this family of ternaries is restricted only to those with the primitive crystallographic
unit cells. For each compound the superconducting state seems to have a conventional
BCS character, in concert with the literature reports [2,3].
References:
[1]Y Zou et al., Phys. Status Solidi RRL 8, 928 (2014).
[2]R. N. Shelton et al., Solid State Commun. 52, 797 (1984).
[3]M. Vališka et al., J. Phys. Soc. Jpn. 81, 104715 (2012).
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Vortex states in a superconductor under a helical magnetic field
Saoto Fukui1, Masaru Kato1, Yoshihiko Togawa2,
1
2
Department of Mathematical Sciences, Osaka Prefecture University, Sakai, Osaka, Japan
Department of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka, Japan
A chiral helimagnet attracts much attention recently. In the chiral helimagnet
magnetic moments form a helical rotation along one direction, and also form a soliton
lattice under a homogeneous applied magnetic field [1]. In a recent work, it was
reported that a chiral helimagnet Cr1/3NbS2 has the superconductivity at the very low
temperature [2]. It is considered that in this system a chiral helimagnet / superconductor
bilayer system is formed. Also, the effect of the chiral helimagnet on the
superconductivity was observed. So, we can expect some singular properties of the
superconductor [3].
In this work, we study effects of the chiral helimagnet on the superconductor. In
particular, we focus on vortex states of the superconductor. To investigate them, we
consider a superconductor under a helical magnetic field from the chiral helimagnet.
We solve the Ginzburg-Landau equations,
and obtain vortex states in the superconductor under the helical magnetic field. We
show how the helical magnetic field changes the vortex states.
This work was supported by JSPS KAKENHI Grant Number 26400367.
Reference:
[1] Y. Togawa, et al., Phys. Rev. Lett. 108 (2012) 107202
[2] Y. Togawa, et al., JPS 2014 autumn meeting at Chubu University
[3] S. Fukui, M. Kato, and Y. Togawa, Physics Procedia, 65, 85 (2015)
Email: [email protected]
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Type-I superconductivity in KBi2 single crystals
Shanshan Sun1, Kai Liu1, Hechang Lei1
1Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials
& Micro-nano Dvices, Renmin University of China, Beijing 100872, China
In condensed matter physics, superconductivity is always one of most attractive
topics. For most of superconducting compounds, they belong to the type-II
superconductors (SCs) and have been studied extensively. In contrast, type-I SCs are
thought empirically to occur mainly in elementary metals and metalloids and type-I
superconducting compounds are very rare. However, more binary and ternary
compounds are found to be type-I SCs, for instance, YbSb2, TaSi2, LaRh2Si2, LaRhSi3,
ScGa3 and LuGa3. These studies break the empirical relation between type-I
superconductivity and elemental metals and enlarge the family of type-I SCs to binary
and ternary compounds. For KBi2 with MgCu2-type (Laves phase) structure, except
superconducting transition temperature Tc, the studies on its physical properties are
scarce and its classification of superconductivity has not been identified yet. In this
work, we performed transport, magnetic, thermodynamic properties and theoretical
calculation of KBi2 single crystals in superconducting and normal states. KBi2 shows
metallic behavior at normal state and enters superconducting state below Tc = 3.573 K.
Moreover, KBi2 exhibits low critical fields in all of measurements, field-induced
crossover from second to first-order phase transition in specific heat measurement,
typical magnetization isotherms of type-I SCs, and small Ginzburg-Landau parameter
кGL = 0.611 < 1/√2. All results undoubtedly indicate that KBi2 is a type-I
superconductor in the dirty limit with thermodynamic critical field Hc = 234.3(3) Oe.
As far as we know, this is the first type-I SC in the bismuth compounds.
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Magnetic fluctuations of Ru1-xRhxP investigated by 31P NMR
Shang Li1, Yoshiaki Kobayashi1, Masayuki Itoh1, Daigorou Hirai2, Zenji Hiroi2, Hidenori
Takagi3,4
1
Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Japan
2
3
Department of Physics, Graduate School of Science, Tokyo, University of Tokyo
4
Ru1-xRhxP was recently reported to have metallic (M), pseudo-gap metallic (PGM),
non-magnetic insulating, and superconducting (SC) phases [1]. It is noted that the SC
transition emerges above x~0.3 and the transition temperature Tc shows a maximum
value of 3.7 K when the PGM phase disappears. We report the results of 31P nuclear
magnetic resonance (NMR) measurements on polycrystalline Ru1-xRhxP to study the
relation between magnetic fluctuations and SC. The temperature T and x dependences
of the 31P Knight shift and the nuclear spin-lattice relaxation rate indicate that an
antiferromagnetic fluctuation enhances in the low-T region of the PGM phase. On the
other hand, the x=0.5 sample with Tc=3.5 K in the M phase has almost no magnetic
fluctuations. Moreover, we also report NMR studies on a single crystal of RuP with a
metallic ground state different from that of the polycrystalline sample [2].
References:
[1] D. Hirai et al., PRB 85, 140509 (2012)
[2] R.Y. Chen et al., PRB 91, 125101 (2015); G.Y. Fan et al., Chin. Phys. Lett 32,
077203 (2015)
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Odd-frequency superconductivity in a nano-sized superconductor under an
external magnetic field
Masaru Kato, Masataka Kashiwagi
Department of Mathematical Sciences, Osaka Prefecture University, Sakai, Osaka, Japan
Recently, much attention focused on odd frequency superconductivity. It was studied by Berezinskii
for the 3He superfluid phase [1]. Then Balatsky et al. studied it for conduction electrons in bulk systems
[2]. Tanaka and coworkers [3] studied odd frequency pairing amplitude in vicinity of boundaries of
unconventional superconductors, where spatial inversion symmetry is broken. In such case, even- and
odd parity Cooper pairings are mixed and then even and odd frequency pairings are mixed. Matsumoto
et el. investigated odd frequency order parameter in a bulk superconductor under an external magnetic
field with an electron-phonon interaction [4,5]. In this case, time reversal symmetry is broken and then
spin singlet and triplet pairing are mixed. And due to the retarded electron-electron interaction that
comes from the electron-phonon interaction, there appears frequency dependence of order parameter.
In this study, we consider nano-sized superconducting plates under an external field. In this case, the
external field well penetrates in to the superconductors. Therefore, if the interaction between electrons
has frequency dependence, the superconducting order parameter is expected to have an odd frequency
component. In order to investigate this odd frequency superconductivity, especially its spatial
dependence, we solve numerically the Eiashberg equation using the finite element method [6]. And we
investigate how spatial dependence of the odd frequency order parameter depends on the strength of the
field and shape of superconductor. Also we investigate the odd frequency order parameter around a
single vortex.
Reference:
[1] V. L. Berezinskii, JETP Lett. 20 (1974) 287.
[2] A. V. Balatsky, E. Abraham, Phys. Rev. B 45 (1992) 13125.
[3] Y. Tanaka, M. Sato, N. Nagaosa, J. Phys. Soc. Jpn. 81 (2012) 011013.
[4] M. Matsumoto, M. Koga, H. Kusunose, J. Phys. Soc. Jpn. 81 (2012) 033702.
[5] M. Matsumoto, M. Koga, H. Kusunose, J. Phys. Soc. Jpn. 82 (2013) 034708.
[6] M. Kashiwagi, M. Kato, Phys. Proc. 65 (2015) 33.
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Spontaneous edge current in a small chiral superconductor witha rough surface
Shu-Ichiro Suzuki1 and Yasuhiro Asano1,2,3
1
1
Department of Applied Physics, Hokkaido University, Sapporo 060-8628, Japan
Center for Topological Science & Technology, Hokkaido University, Sapporo 060-8628, Japan,
3
Moscow Institute of Physics and Technology, 141700 Dolgoprudny, Russia
We study theoretically the spontaneous edge current in a small chiral superconductor with surface
roughness. We obtained self-consistent solutions of the pair potential and the vector potential by solving
the quasiclassical Eilenberger equation and the Maxwell equation simultaneously. We then employed
them to calculate numerically the spatial distribution of the chiral edge current in a small superconductor.
The characteristic behavior of the spontaneous edge current depends strongly on the symmetries of the
order parameters such as chiral p-, chiral d- and chiral f-wave pairing. The edge current is robust under
the surface roughness in the chiral p- and chiral d-wave superconductors. In the chiral d-wave case, the
surface roughness tends to flip the direction of the chiral current. On the other hand, the edge current in
a chiral f-wave superconductor is fragile when there is surface roughness. We also discuss the
temperature dependence of a spontaneous magnetization, which is a measurable value in standard
experiments.
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High Tc in hydrogen sulfide under pressure as a result of the formation of
hydrogen planes in the crystal
Evgeny Mazur1, Nikolay Degtyarenko1
1
National Research Nuclear University (Moscow Engineering Physics Institute), Kashirskoe sh.31, Moscow115409,
Russia
Eliashberg theory generalized for the account of the peculiar properties of the finite zone width
electron-phonon (EP) system with the non constant electron density of states, the electron-hole
nonequivalence, chemical potential renormalization with frequency is used for the study of the most
general properties of the normal and superconducting properties of the hydrogen sulfide electron-phonon
system. The pairing within the full width of the electronzone was taken into account, not just on the
Fermi surface. It is shown that all the necessaryconditions for the manifestation of the high
superconducting transition temperature are ideally implemented in the hydrogen sulfide under high
pressure. The results of the calculations of the electron and phonon properties of the most
thermodynamically favorable phase of hydrogen sulfide under pressure are used. These results are
applied to the calculation of the superconducting properties of hydrogen sulfide under pressure. As we
can see the Fermi level is located near the electron density peak of the s-type states corresponding to the
high Tc value. Most part of s-type states refers to the hydrogen. In this case a sharp decrease in the
density of electron state is distinctly seen above the Fermi energy in the system. The phonon dispersion
and the density of phonons (DOS) are shown vs energy for the pressure P=165 GPa . For P = 175 GPa
the pictures of phonon dispersion and the density of phonons (DOS) are very similar. Two narrow peaks
with phonon mode energies can be seen at the phonon density of states high-frequency region. Only one
of these two peaks is active in the infrared absorption. The calculated phonon spectrum is shown for the
pressure P = 180 GPa. As one can see, the one of the acoustic branches of the phonon spectrum tends to
zero value for this pressure, and the calculated phonon frequency turns to "negative" values (imaginary
values in reality), indicating the instability of the selected orthorhombic phase near the given pressure.
This result is fully consistent with the experimental results[1] , where at the pressure P = 180GPa the
phase transition point for this system was detected. The detailed analysis of changes of this structure
with increasing pressure shows that the specific feature of this structure should be the formation of the
system of parallel planes with the full-body concentration of hydrogen atoms in these planes at the
pressure P = 150 – 170 GPa. As a result, the electron properties of the system acquire quasi-twodimensional character. Only three modes have non-zero intensity of interaction with infrared light from
the six lattice vibrational modes (ν[cm-1]: 309.43; 309.43; 1169.91; 1169.91; 2306.72; 2420.94). Two
modes with maximum frequencies correspond to the conditions for the high critical temperature Tc for
the given SH2 phase. The vibrations of atomic plane consisting of hydrogen atoms with the frequency
ν1 = 2420.94 [cm-1] have zero intensity in infrared radiation. It is found that the finiteness of theelectron
zonewidth in the derived anew Eliashberg equations for the finite zone width EPsystem together with
the abrupt fall of the density of states above the Fermi surface are the crucial factors for the high
temperature superconductivity appearance.
References:
1.A.P.Drozdov,M.I.Eremets, I.A.Troyan.Conventional Superconductivity at 190 K at high
pressures, Arxiv, cond.mat, 14.12.0460.
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Spin-valley locking in the normal state of a transition-metal dichalocogenide
superconductor
L.Bawden,1 S. Cooil,2 F. Mazzola,2 J. M. Riley,1;3 L. Collins-McIntyre,1 V. Sunko,1;4 K. Hunvik,2 M.
Leandersson,5 C. Polley,5 T. Balasubramanian,5 T. K. Kim,3 M. Hoesch,3J. W. Wells,2 G. Balakrishnan,6
M. S. Bahramy,7;8 and P. D. C. King1
1
2
SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, UK
Dept. of Physics, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway
3
Diamond Light Source, Harwell Campus, Didcot, OX11 0DE, United Kingdom
4
Max Planck Institute for Chemical Physics of Solids, N•othnitzer Stra e 40, 01217 Dresden, Germany
5
MAX IV Laboratory, Lund University, P. O. Box 118, 221 00 Lund, Sweden
6
Dept. of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
7
Quantum-Phase Electronics Center and Dept. of Applied Physics, University of Tokyo, Tokyo, Japan
8
RIKEN center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
2H-NbSe2 is a metallic transition metal dichalcogenide, which hosts instabilities to a charge density
wave phase at 33 K, and exhibits superconductivity at 7 K.1 The origins and nature of these collective
states have been fervently debated since their discovery four decades ago. To date, they have been
assumed to emerge from a normal state of spin-degenerate quasiparticles. In contrast, from spin- and
angle-resolved photoemission measurements, supported by rst principles calculations, we reveal that the
normal state Fermi surface hosts a complex spin texture. We uncover a rich spin-valley locking of the
form also observed in the semiconducting materials of the same family,2 5 and consistent with the recent
observation of so-called Ising pairing in the superconducting state of monolayer NbSe2.5 We find that
for the bulk compound there is persistent spin polarisation, despite the centrosymmetric crystal structure
that would conventionally be expected to forbid this. We show how the degree of spin polarisation
becomes intrinsically linked to the electronic dimensionality, showing a significant dependence on the
out-of-plane momentum. This prompts a reinterpretation of the mechanism for and properties of the
collective phases in this and related materials.
Figure 1: Spin-valley locking in NbSe2 (a) Measurement of the normal-state Fermi surface of NbSe2
from angle-resolved photoemission. (b) Spin-resolved momentum distribution curve along the cut
indicated in (a) showing strong out-of-plane spin polarisation of the bands crossing the Fermi level.
References:
[1] Wilson, J. A, Di Salvo, F. J. and Mahanjan, S., Phys. Rev. Lett. 32 16 (1974).
[2] Xu, X et al., Nature Phys. 10 5 (2014).
[3] Mak, K. F. et al., Science 344 6191 (2014).
[4] Riley, J. M. et al., Nature Phys. 10 11 (2014).
[5] Xi, X. et al., Nature Phys. Advanced Online Publication (2015) DOI:10.1038/nphys3538
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Unusual Disorder Effect in Parity Mixing Superconductors Li2 T3 B
(T: Pd, Pt) with Noncentrosymmetric Crystal Structures
G. Bao1, Y. Inada2,3, G. Eguchi4, Y. Maeno5, G-q. Zheng3,6
1
The college of Physics and Electronic Information, Inner Mongolia University For The
Nationalities, Tongliao of Inner Mongolia, China
2
Graduate School of Education, Okayama University, Japan
3
Department of Physics, Okayama University, Japan
4
Institute of Solid State Physics, Vienna University of Technology, Austria
Department of Physics, Graduate School of Science, Kyoto University, Japan
6
Institute of Physics and Beijing National Laboratory for condensed Matter Physics, Chinese
Academy of Sciences, Beijing, China
5
Superconductivity in the absence of inversion crystal symmetry attracts particular
interesting in possibility mixture of spin singlet and spin triplet state. The NMR [1, 2],
penetration depth [3] and specific heat [4] measurements have found there exist nodes
in the gap function Li2 Pt 3 B while Li2 Pd3 B is a conventional BCS superconductor.
Especially, knight shift and penetration depth measurement suggested that Li2 Pt 3 B is
a spin triplet dominant superconductor with the ratio of singlet to triplet order parameter
was estimated as 0.6, while Li2 Pd3 B is an s-wave spin singlet dominant
superconductor with the ratio of 4. It is known that s-wave superconductor is robust
against disorder, while non s-wave superconductor is strongly affected. The disorder
effect of parity mixing superconductor is still unclear. We have reported there are clear
differences betweenLi2 Pt 3 B andLi2 Pd3 B in sample quality dependence of the H-T
superconducting phase diagrams [5]. Li2Pd3B exhibited the weak Tc suppression
attributed by disorder, while Hc2 (0) value increased about 1.5 times larger in the low
quality samples, while both the Tc and Hc2 were suppressed by disorder in Li2Pt3B. It
was suggested that the Cooper pair was broken by disorder in Li2 Pt 3 B. However, the
rate of Tc suppression by disorder has been found to be not so large to be explained by
the pair-breaking effect expected for the non s-wave superconductor. We will report
the unusual disorder effect in Li2 T3 B. Condensation energies are estimated from the
thermodynamic critical field of Hc. We will discuss possibilities of mechanisms which
produce robustness against disorder in parity mixing superconductors.
Reference:
[1] M. Nshiyama, Y. Inada and G-q. Zheng, Phys. Rev. B 71, 220505 (2005)
[2] M. Nshiyama, Y. Inada and G-q. Zheng, Phys. Rev. Lett. 98, 047002 (2007)
[3] H. Q. Yuan, et.al, Phys. Rev. Lett. 97, 017006 (2006)
[4] H. Takeya, et al., Phys. Rev. B 76, 104506 (2007)
[5] G. Bao, Y. Inada, G. Eguchi, Y. Maeno, M. Ichioka, G-q. Zheng, Physica C.
494, 95-98 (2013)
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Effect of Hopping Disorder on Mott Phase of 1T-TaS2
Yang-Yang Zhao1, Yang Yu, Yun Song1
1
Department of Physics, Beijing Normal University, Beijing, China
The bulk 1T-TaS2 is known to develop a peculiar Mott phase at low temperature. We
first use the kernel polynomial method to study the localization effect of the hopping
disorder of the transition-metal dichalcogenide with disordered layer stacking. At the
center of the energy band, the scaling of the generalized inverse participation ratio is
found to be very sensitive to the energy broadening of Lorenz kernel, indicating that
the localization of the intermediate state is abnormal. Secondly, we employ the realspace dynamical mean-field theory to study the cooperative effect of the electronelectron interactions and the hopping disorder on the Mott phase of the bulk 1T-TaS2.
We find that the Mott gap survives the strong off-diagonal disorder, which rules out the
possibility of a metallic phase introduced by the disordered layer stacking. Thirdly, we
discuss the possible gate-tunable phase transition by observing the evolution of the
optical conductivity with the decreasing carrier concentration.
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Curie-Temperature Enhancement in Electron-Doped EuO
Tobias Stollenwerk1,2 and Johann Kroha1,3
1
Physikalisches Institut and Bethe Center for Theoretical Physics, University of Bonn, Germany
2
German Aerospace Center, Cologne, Germany
3
Center for Correlated Matter, Zhejiang University, Hangzhou, China
Due to its simultaneous ferromagnetic and insulator-to-metal transition, electrondoped EuO is among the materials with the strongest magneto-electrical and magnetooptical responses known in nature. To make these outstanding properties accessible for
widespread applications, it is desirable to raise the Curie temperature to the range of
room temperature.
We present a comparative, theoretical study of the doping dependence of the critical
temperature TC of the ferromagnetic insulator-metal transition in Gd-doped and in Odeficient EuO, respectively [1]. The strong TC enhancement in Eu1−xGdxO is due to
Kondo-like spin fluctuations on the Gd sites, which are absent in EuO1−x. Moreover, we
find that the TC saturation in Eu1−xGdxO for strong doping x is due to a reduced
activation of dopant electrons into the conduction band, in agreement with experiments
[2], rather than antiferromagnetic long-range contributions of the RKKY interaction.
The results shed light on possibilities for further increasing TC.
References
[1]T. Stollenwerk, J. Kroha, Phys. Rev. B 92, 205119 (2015).
[2]T. Mairoser, A. Schmehl, A. Melville, T. Heeg, L. Canella, P. Böni, W. Zander, J.
Schubert, D. E. Shai, E. J. Monkman, K. M. Shen, D. G. Schlom, J. Mannhart, Phys.
Rev. Lett. 105, 257206 (2010).
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Spin-Fluctuation Mechanism of Insulator-Metal Transition of Strongly
Correlated Paramagnetic Compounds with pd-Hybridization
A.A. Povzner, A.G. Volkov1
1
Ural Federal University, Ekaterinburg, Russia
We investigate the transition of strongly correlated paramagnetic insulator with
hybridization gap in the metallic state. It is shown that the hybridization of the electron
spin states occurs in addition to the hybridization of states of p- and d-electrons. In
insulator phase spin density d-like electrons fluctuates without breaking the singlet state
of the valence band, which is separated from the conduction band of hybridization gap.
Therefore, the static spin susceptibility is zero, and the electronic specific heat increases
with temperature due to the dynamic spin fluctuations. The temperature increase
fluctuations of electronic density leads to d-like states inside the hybridization gap. In
metallic phase, spin susceptibility appears and increases with temperature. The number
occupied d-like states change with temperature that generates a maximum of electronic
heat capacity. Numerical calculations show that this picture is consistent with the results
of experimental studies and ab initio calculations of the electronic structure of FeSi.
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Melted insulator state under pressure in layered structured
compounds (Eu3-nSrn)Bi2S4F4 (n = 1 and 2)
Bosen Wang1, K. Ishigaki,1 K. Matsubayashi,1,2 G. Kalai Selvan3, Zeba Haque4, A. K.
Ganguli4,5,S. Arumugam,3 and Y. Uwatoko1
1
Institute for Solid State Physics, University of Tokyo, Japan
Department of Engineering Science, University of Electro-Communications, Japan
3
Centre for High Pressure Research, School of Physics, Bharathidasan University, India
4
Department of Chemistry, Indian Institute of Technology New Delhi, India
5
Institute of Nano Science and Technology, India.
2
Hydrostatic pressure effect on the insulator (Eu3-nSrn)Bi2S4F4 (n= 1, 2) was studied
in a multiple-anvil cell up to 15 GPa. As increasing the pressure, the resistivity
decreases monotonously and the insulator was melted into metallic behavior at critical
pressures. Meanwhile, some superconducting indications emerge at lower temperature
and its characteristic temperature depends on pressure. Pressure-temperature diagram
was studied by combining with the evolutions of crystal structure and magnetic
properties under high pressure.
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Fano resonance in Spin-Orbit coupled Mott Insulating System
Sr2IrO4: a Raman Study
Dileep Kumar Mishra1,2,3
1
Department of Condense Matter Physics & Material Sciences,Tata Institute of Fundamental
2
Research, Mumbai India 400005
3
Department of Physics, Indian Institute of Science Education and Research, Bhopal India
Raman laboratory, UGC DAE Consortium of Scientific Research, Indore, India
Present study highlights the influence of electron phonon (e-ph) interaction on the
ground state and low energy excitations of 5d iridates. Sr2IrO4 is a prototype strongly
spin orbit driven Mott insulating system [1], here investigated in detail by low
temperature polarized Raman spectroscopy. All Γ-point phonon modes and its
symmetry well collaborates with group theory. Observed asymmetric line shape of the
Raman modes owing to Fano resonance [2] evidenced e-ph interaction. Fano
asymmetry increased sharply above the magnetic ordering temperature, implies that
pseudo spin degrees of freedom forms electronic continuum in the paramagnetic state
that strongly interfere with low energy lattice vibrations. Therefore. Strong spin orbit
coupling is not sufficient to seize the orbital fluctuations in the paramagnetic state.
Furthermore, magnetic order induced renormalization of phonon frequencies signifying
presence of spin phonon coupling and two magnon excitation are also observed in
Raman spectra below magnetic transition temperature.
References:
[1]B.J. Kim et al, Phys. Rev. Lett. 101, 076402 (2008).
[2]U. Fano, Phys. Rev. 124, 1866 (1961).
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Metal insulator transition of pyrochlore iridate Ln2Ir2O7 studied by
ARPES
M. Nakayama1, Takeshi Kondo1, Z. Tian1, J.J. Ishikawa1, M. Halim1, C. Bareille1, W.
Malaeb1,2, K.Kuroda1, T. Tomita1, S. Ideta3, K. Tanaka3, M. Matsunami4, S. Kimura5,
N. Inami6, K. Ono6, H.Kumigashira6, L. Balents7, S. Nakatsuji1,8, and S. Shin1
1
ISSP, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
Physics Department, Faculty of Science, Beirut Arab University, Beirut, Lebanon
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Toyota Technological Institute, Nagoya 468-8511, Japan
5
Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, 565-0871,
Japan
6
Institute of Materials Structure Science, High Energy Accelerator Research
Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
7
Kavli Institute for Theoretical Physics, Santa Barbara, California 93106, USA
8
CREST, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi,
Saitama 332-0012, Japan
2
We present an angle-resolved photoemission study of the electronic structure of the
three- dimensional pyrochlore iridate Nd2Ir2O7 through its magnetic metal-insulator
transition. Our data reveal that metallic Nd2Ir2O7 has a quadratic band, touching the
Fermi level at the Γ point, similarly to that of Pr2Ir2O7[1].Upon cooling below the
transition temperature, this compound exhibits a gap opening with an energy shift of
quasi-particle peaks like a band gap insulator. The quasi-particle peaks are strongly
suppressed, however, with further decrease of temperature, and eventually vanish at the
lowest temperature, leaving a non-dispersive flat band lacking long-lived electrons. We
thereby identify a remarkable crossover from Slater to Mott insulators with decreasing
temperature [2].
Reference:
[1] T. Kondo et al., Nature Communications 6,10042 (2015).
[2] M. Nakayama et al., arXiv:1603.06095 (2016).
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High Pressure Quantum Oscillation Studies of the Metallised Mott
Insulator NiS2
Hui Chang1, Jordan Baglo1, Alix McCollam2, Inge Leermakers2, Xiaoye Chen1, HongEn Tan1,
Pascal Reiss1, Sven Friedemann3, Monika Gamza4, Patricia Alireza1, William Coniglio5, David
Graf5, Stanley Tozer5, and F. Malte Grosche1
1
Cavendish Laboratory, University of Cambridge, UK.
High Field Magnet Laboratory, Nijmegen, The Netherlands.
3
HH Wills Laboratory, University of Bristol, UK.
4
Jeremiah Horrocks Institute for Mathematics, Physics and Astrophysics,University of Central
Lancashire,UK.
5
National High Magnetic Field Laboratory, Tallahassee, Florida, USA.
2
The transition from a metallic to a Mott insulating state is a longstanding theme of
fundamental interest in condensed matter research. Yet, the detailed description of the
transition remains unresolved. This, coupled with the emergence of novel phenomena
- such as high-Tc superconductivity - in the vicinity of the transition has continued to
motivate experimental and theoretical studies toward a more precise understanding of
Mott physics.
One of the most basic questions concerns the evolution of the Fermi surface and the
carrier effective mass in the correlated metallic state near the Mott transition. Quantum
oscillation measurements present a direct probe of the Fermi surface, and pressure
rather than doping should be used as the tuning parameter in this case. We investigate
this question in the Mott insulator NiS2, which becomes metallic at a moderate pressure
of 30 kbar. Using the tunnel diode oscillator technique in conjunction with high pressure
anvil cells, we have observed quantum oscillations at pressures between 38 kbar and
50 kbar in magnetic fields up to 31T. This enables us to resolve key elements of the
Fermi surface of high pressure NiS2 and to obtain estimates of the effective carrier mass
on different Fermi surface sheets. Moreover, we discuss the evolution of the Fermi
surface, the carrier effective mass and the relaxation time with applied pressure within
the pressure-metallised correlated state.
410
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Switching of electronic states due to cooperation between hydrogen
-bond dynamics and π-electrons in a purely organic conductor
Kenichiro Hashimoto1, Keisuke Itoh1, Ryota Kobayashi1, Megumi Kurosu1, Satoshi Iguchi1,
Takahiko Sasaki1, Kensuke Kobayashi2, Reiji Kumai2, Youich Murakami2, Akira Ueda3, Hatsumi
Mori3
1
Institutes for Materials Research,Tohoku University, Sendai, Japan
The Institute for Solid State Physics, The University of Tokyo, Kashiwa , Japan
3
Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK),
Tsukuba, Japan
2
A purely organic conductor κ-H3(Cat-EDT-TTF)2 has spurred great interest as a new
spin liquid candidate [1,2]. The most striking feature of this system is that the 2D πelectron layers of the Cat-EDT-TTF molecules are connected by the hydrogen bonds.
In this system, the quantum tunneling of the proton between the double minimum
potential of the hydrogen bonds may play an important role for the quantum
paramagnetic state. Recently, it has been reported that hydrogen/deuterium substitution
of the hydrogen bonds induces a charge disproportionation associated with deuterium
localization [3], which highlights a strong coupling between the hydrogen-bond
dynamics and the π-electronic system. Here we report a phase transition observed in κH3(Cat-EDT-TTF)2 with slightly different lattice parameters from the spin liquid
compound. The X-ray crystal structure analysis demonstrates a displacement of the
hydrogen atom at 50 K, which causes a change of electronic states from the Mott
insulating state to a band insulating state. The infrared-visible optical experiments have
revealed a drastic thermochromism associated with hydrogen-bond-based switching of
the electronic structure. We discuss novel phenomena caused by cooperation between
the hydrogen-bond dynamics and the π -electrons.
Reference:
[1]T. Isono et al., Nature Commun. 4, 1344 (2013).
[2]T. Isono et al., PRL 112, 177201 (2014).
[3]A. Ueda et al., JACS 136, 12184 (2014).
411
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A New Family of Quasi One-dimensional Organic Conductors
(BPDT-TTF)2X
R. Kobayashi1, K. Hashimoto1, N. Yoneyama2, H. Taniguchi3, B. Wang4, Y. Uwatoko4, T. Sasaki1
1
2
Institute for Materials Research, Tohoku University, Miyagi, Japan
Faculty of Engineering, University of Yamanashi, Yamanashi, Japan
3
Faculty of Science, Saitama University, Saitama, Japan
4
Institute for Solid State Physics, University of Tokyo, Tokyo, Japan
Most of organic conductors are recognized as low dimensional strongly correlated
electron systems, in which various exotic ground states such as charge order,
magnetic order, and unconventional superconductivity can be realized. Since applying
physical pressure as well as chemical pressure can tune the ground states, pressure
effects play an essential role to understanding the origins of these electronic states.
Therefore, development of a new family of organic conductors whose physical
properties are systematically tunable by chemical and physical pressure is important
for investigating strongly correlated electron systems.
Here we focus on a new family of quasi one-dimensional organic conductors (BPDTTTF)2X (X = I3, IBr2, ICl2, AuCl2, CuCl2). Band structure calculations using the tightbinding approach based on the extended Hückel method demonstrate that the electronic
structure of these salts can be classified into a 3/4-filled and an effective 1/2-filled
system depending on the degree of dimerization. Our optical conductivity
measurements have revealed that the ground state of the 3/4-filled system is in a charge
ordered insulating state, while a dimer-Mott insulating state emerges in the 1/2-filled
system. Moreover, in order to investigate the physical pressure effect in addition to the
chemical pressure effect, we have performed resistivity measurements under high
pressure using a cubic-anvil type cell, which reveal that a one-dimensional metallic
state appears above 4 GPa at room temperature and a dimensional crossover from 1D
to 2D emerges above 5 GPa. We will discuss the obtained p-T phase diagram of the
quasi one-dimensional organics (BPDT-TTF)2X in terms of both chemical and physical
pressure effects.
412
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Solid hydrogen metallization as a Mott transition from exact
diagonalization - ab initio approach
A. Biborski1, A. P. Kądzielawa2
1
and J. Spałek1,2
Academic Centre for Materials and Nanotechnology, AGH University of Science and Technology,
al. A. Mickiewicza 30, 30-059 Krakow, Poland
2
Marian Smoluchowski Institute of Physics, Jagiellonian University, ulica Łojasiewicza 11, 30348 Kraków, Poland
We discuss a transition of solid molecular hydrogen to the quasiatomic state [1]. The
transition is modeled on finite-size one- and two-dimensional systems, with inclusion
of the long-range Coulomb interaction between electrons. The method of approach
combines exact diagonalization in the Fock space with an ab initio readjustment of the
single-particle wave functions in the correlated state (the EDABI method [2,3]). The
system is characterized by the effective bond length R and the intermolecular distance
a, both optimized for given applied force (pressure). It is shown that those system
undergo a discontinuous transition from a molecular phase (R≪a) to the quasiatomic
phase with R ~ a. This transition is accompanied by a jump in the ratio of the Hubbard
interaction U to the bare bandwidth from the value $U/W ~ 1.5 to the value <1. We
interpret this fact as a Mott-Hubbard transition to the correlated almost localized Fermi
liquid. In distinction to the canonical insulator--metal transition as a function of
pressure, here the insulating phase is nonmagnetic (diamagnetic), not antiferromagnetic.
The work was supported by the National Science Centre (NCN), Grant No. DEC2012/04/A/ST3/00342.
Reference:
[1]A. P. Kądzielawa, A. Biborski, and J. Spałek, Phys. Rev. B 92, 161101(R) (2015)
[2]A. P. Kądzielawa, et al., New J. Phys. 16, 123022 (2014)
[3]A. Biborski, A. P. Kądzielawa, and J. Spałek, Comp. Phys. Commun. 197, 7-16
(2015)
413
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Metal-insulator transition and spectroscopy of LaCoO3: realistic
many-body approaches
E. Gorelov1, I. Krivenko1,2, M. Izquierdo1,2, A. I. Lichtenstein1,2, S. L. Molodtsov1,3
1
2
European XFEL GmbH, 22761 Hamburg, Germany
I. Institut für Theoretische Physik, Universität Hamburg, 20355 Hamburg, Germany
3
ITMO University, 197101 St. Petersburg, Russia
Rare-earth cobaltates are of great interest nowadays, due to their rich phase diagram,
including metal-to-insulator transitions, and variety of technological applications, e.g.
as a catalytic materials, or as an electrodes for batteries, photovoltaic devices, sensors,
etc.
One of the interesting examples of these materials is LaCoO3 (LCO), that has
perovskite structure and undergoes a metal-insulator transition around T~500 K and a
gradual spin-state transition around T~80-120 K.
One of the main theoretical challenges, arising in the electronic structure calculations,
is the interplay between localized and itinerant behavior of Co 3d orbitals, leading to
all the variety of electronic structure transitions with change of a control parameter, e.g.
temperature or pressure. This makes calculation of the electronic structure and
corresponding spectroscopic properties a very interesting and nontrivial task.
One of the ways to tackle this problem, is using the LDA+DMFT method, that maps
the problem of correlated lattice of Co 3d orbitals in the crystal to effective single-site
problem with material-specific parameters, that could be calculated ab initio. This
method is able to treat multi-orbital on-site Coulomb interaction, responsible for the
multiplet structure. Using this approach we could study details of the metal-to-insulator
transition in LCO and calculate orbital-dependent spectral function of Co 3d bands at
different pressures and temperatures [1,2]. We found, that the gap opens first in eg bands,
while t2g bands still remains conducting.
Another theoretical method, allowing the calculation of spectroscopic properties of
LCO is the approach of M. Haverkort, taking into account transition metal ion and its
octahedral oxygen surrounding [3]. This approach allows us to calculate the resonant
Co L2,3 X-ray absorption spectra (XAS), using ab initio calculated model parameters,
i.e. nearest neighbors hopping matrix. Using this approach we calculate Co L2,3 XAS
for different temperatures in the range of 80-600 K. In our calculations we include Co
3d orbitals with full Coulomb vertex, and five ligand orbitals, constructed from 2p
orbitals of O atoms, forming the octahedra around Co ion. We analyze features in the
XAS spectra, and attribute them to thermal expansion of the lattice, change of electron
temperature, and low-spin to high-spin transition. We compare calculated XAS spectra
to recent experimental results and analyze effects caused by proximity of the crystal
surface.
References:
[1]G. Zhang, E. Gorelov, E. Koch, and E. Pavarini, Phys. Rev. B 86, 184413 (2012)
[2]M. Karolak, M. Izquierdo, S. L. Molodtsov, A. I. Lichtenstein Phys. Rev. Lett.
115, 046401 (2015)
[3] M. W. Haverkort, M. Zwierzycki, and O. K. Andersen PRB 85, 165113 (2012)
414
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Magnetoresistivity in Nanobridges of Сompounds with Magnetic
Phase Separation
Yu. Goryunov1
1
Self-localization effects of current carriers or a ferrons formation in narrow -band
magnetic semiconductors and semimetals arise due the interaction of different types of
carriers with the magnetic ions and they cause to the small-scale magnetic phase
separation [1] on the dielectric and metal regions. A consequence of this phase
separation is colossal negative magnetoresistance. EuB6 is a classic representative of
compounds with colossal magnetoresistivity, along with manganites. We performed an
experiment in which by the same measuring current of 15 μA we have simultaneously
measured the magnetoresistivity of a bulk single crystal along the direction [100] and
of a nanobridge along the direction [111]. In absolute values, the resistances of bulk
EuB6 sample and EuB6 nanobridge differed by 4 orders of magnitude but temperature
behavior was similar. However, the influence of magnetic field on the resistance of two
conductors, connected by the same current, was very different. In the case of a bulk
EuB6 at 15 K, we observed previously known value of about -60%, whereas for EuB6
nonobridge hexaboride this value was about -15%. Taking in attention [2], we are
explaining this result by the closeness of sizes of nanobridge and ferron, causing a
quantity of ferrons participating in the conductivity is decreased and we are regarding
it as direct evidence of the existence of ferrons in EuB6.
Reference:
[1]M. Yu. Kagan, A. V. Klaptsov et al., Phys.–Uspekhi, 46(8) 851(2003)
[2]A.O. Sboychakov, et al., J.Phys.: Cond.Mat. 22 415601(2010)
415
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High-performance channel-decomposed renormalization group
scheme for fermions on two-dimensional lattices
Julian Lichtenstein1, Carsten Honerkamp1
1
Institute for Theoretical Solid State Physics, RWTH Aachen University, Germany
The truncated unity functional renormalization group (TUfRG) approach is a novel
functional renormalization group (fRG) variant for interacting fermions. It is based on
an exchange parametrization of the two-fermion interaction [1], while the structure of
the equations and some more advantageous aspects are inspired by the singular-mode
functional renormalization group put forward by Wang et al.[2]. On the basis of speedup
data gained from our implementation we show that the TUfRG facilitates efficient
calculations on a large number of multi-core CPUs. In this context, it will be illustrated
that a separation of the underlying equations as done here is numerically advantageous.
In order to discuss the virtues this method, we compare data for the t,t’ Hubbard model
on the square lattice to those from other fRG methods. Furthermore, we analyze the
effects of including longer ranged interactions in addition to the purely local Hubbard
interaction.
This work was supported by DFG (German Research Foundation) via RTG1995
‘Quantum many-body methods in condensed matter systems’.
Reference:
[1]C. Husemann and M. Salmhofer, PRB 79, 195125 (2009)
[2]W. S. Wang et al., PRB 85, 035414 (2012)
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Interaction-driven insulator-to-metal transition in bilayer ionic
Hubbard model
M. Jiang1 and T.C.S. Schulthess1,2
1
2
Institute for Theoretical Physics, ETH Zurich, Switzerland
Swiss National Supercomputing Center, ETH Zurich, 6900 Lugano, Switzerland
The interaction-driven insulator-to-metal transition has been reported in the ionic
Hubbard model (IHM) on square lattice for intermediate interaction $U$, which poses
fundamental interest in the correlated electronic systems. Here we use determinant
quantum Monte Carlo to study the interplay of interlayer hybridization $V$ and two
types of intralayer staggered potentials: one with the same (in-phase) and the other with
a $\pi$-phase shift (anti-phase) potential in two layers termed as ''bilayer ionic Hubbard
model''. We demonstrate that the interaction-driven Insulator-Metal transition extends
to bilayer IHM for both types of staggered potentials. Besides, the system with in-phase
potential is prone to metallic phase with turning on interlayer hybridization while that
with anti-phase potential tends to insulators with strong charge density order.
417
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Detecting phase transitions and crossovers in Hubbard models using
the fidelity susceptibility
Li Huang,1 Yilin Wang,2 Lei Wang,3
and Philipp Werner4
1
Science and Technology on Surface Physics and Chemistry Laboratory, P.O. Box 9-35, Jiangyou
621908,China
2
Beijing National Laboratory for Condensed Matter Physics,and Institute of Physics, Chinese
3
Theoretische Physik, ETH Zurich, 8093 Zurich, Switzerland
4
Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland(Dated: January 15,
2016)
The fidelity susceptibility of single-band and multi-orbital Hubbard models is
systematically studied using single-site dynamical mean field theory in combination
with a hybridization expansion continuous-time quantum Monte Carlo impurity solver.
We find that the fidelity susceptibility is extremely sensitive to changes in the state of
the system. It can be used as a numerically inexpensive tool to detect and characterize
most kinds of phase transitions and crossovers in Hubbard models, such as (orbitalselective) Mott metal-insulator transitions, high-spin to low-spin transitions, Fermiliquid to non-Fermi-liquid crossovers, and spin-freezing crossovers.
PACS numbers: 71.27.+a, 71.10.Hf, 71.10.Fd, 71.30.+h
418
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Mott-Insulator to Superconductor Transition in a Two-Dimensional
Superlattice
Rubem Mondaini1, Marcos Rigol2
1
2
Beijing Computational Science Research Center, Beijing 100084, China
Physics Department, The Pennsylvania State University,104 Davey Laboratory, University Park,
Pennsylvania 16802, USA
We use use quantum Monte Carlo and exact diagonalization calculations to study the
Mott-insulator to superconductor quantum phase transition in a two-dimensional
fermionic Hubbard model (either in square as well in honeycomb lattices) with
attractive interactions in the presence of a superlattice potential. The model introduced
offers unique possibilities to study such transitions in optical lattice experiments and
hints at the possibility of the investigation of pseudogap phenomena with a symmetry
different from the one observed in high-Tc experiments. We show that, in regimes with
moderate to strong interactions, the transition belongs to the 3D-XY universality class.
We also explore the character of the lowest energy charge excitations in the insulating
and superconducting phases and show that they can be fermionic or bosonic depending
on the parameters chosen.
Reference:
[1] Rubem Mondaini, Predrag Nikolić, and Marcos Rigol, Physical Review A, 92,
013601 (2015).
419
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Homologous Multiferroicity in Ca0.5Ba0.5MnO3 from First-Principles
Investigation
Shan Jin1, Di Jin1, Xilian Jin2, Xing Meng1, 2
1
Key Laboratory of Physics and Technology for Advanced Batteries ( Ministry of Education ),
College of Physics, Jilin University, Changchun 130012, P. R. China
2
State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun
130012, P. R. China
The family of ABO3 perovskite oxide compound has attracted widespread concern
in the field of condensed matter physics and materials science because of their diverse
physical properties, which originates from the cooperation and competition among the
different types of ferroic order-parameter. The major problem in multiferroics is the
difficulty of combining ferromagnetism with ferroelectricity in the single phase.
However, combination between two complex oxides could provide a new example of
a material in which charge, spin, lattice and orbital degrees of freedom strongly coupled.
The orthorhombic single phase of CaMnO3 cannot exhibit a spontaneous polarization
at its ground state due to the strong antiferrodistortive ( AFD ) instability, meanwhile,
AFD mode suppress the ferroelectric mode forcefully. Herein by alloying the CaMnO3
and BaMnO3 together, the larger radius Ba2+ ion in Ca0.5Ba0.5MnO3 could successfully
suppress the AFD mode. Due to the weakened inhibition from AFD mode, the
spontaneous polarization is derived from the off-center of symmetry of Mn4+ ion. So
that the origin of the magnetism and ferroelectricity are derived from Mn4+ ion inducing
a homologous of multiferroic magnetic effect, which overcome the disadvantages of
weak magnetoelectric coupling in most of multiferroics. Using the first-principles
simulation, we calculate the energy of the 40 atoms 2×2×2 supercell Ca0.5Ba0.5MnO3
with different magnetic configurations and different cationic ( Ca2+, Ba2+ ) orders based
on density functional theory GGA + U method. The initial structure contains all the
freedom of unstable phonon modes in order to find the accurate ground state structure.
Reference:
[1] D. I. Bilc et al., PRL 96, 147602 (2006)
[2] S. Bhattacharjee et al., PRL 102, 117602 (2009)
[3] J. M. Rondinelli et al., PRB 79, 205119 (2009)
[4] H. Sakai et al., PRL 107, 137601 (2011)
[5] G. Giovannetti et al., PRL 109, 107601 (2012)
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Ferroelectricity and magnetoelectric coupling in h-YbMnO3: Spin
reorientation and Defect effect
Gang Qiang1, Yifei Fang1, Xiaowen Lu1, Shixun Cao1 and Jincang Zhang1*
1
Materials Genome Institute and Department of Physics, Shanghai University, Shanghai 200444,
China
* Corresponding author, E-mails:[email protected]
The hexagonal RMnO3 are usually divided into two classes according to the ionic
radius of the rare earth element. Orthorhombic structure (space group Pnma) is stable
for R=La–Dy and hexagonal structure is optimal for R=Ho to Lu as well as Y and Sc.
We have studied the low-temperature magnetic and electric properties in hexagonal
multiferroic compound YbMnO3. The Mn3+ spin moments order at TN=85K and
reoriented around 43.5 K leading to the magnetic phase transition from
B2(P63cm)→A2(P63cm). The concomitant ferroelectric polarization is observed and
explained microscopically by the destruction of initial symmetric relationship of the
polarization between the upper and lower half of the magnetic unit cell. The asymmetry
of the polarization vs temperature curves under opposite poling voltage revealed the
pinning effect of the defects on the electrical polarization.
421
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X-ray Dichroisms Study of Multiferroic GaFeO3 single crystals
A.Rogalev1, F. Wilhelm1, A. Bosak1
1European Synchrotron Radiation Facility (ESRF), Grenoble, France
Ferroelectric and ferrimagnetic ordering coexist in gallium ferrate - GaFeO3. The
multiferroic properties of this compound have been extensively studies since early
sixties by many different experimental techniques. In order to study these properties on
a microscopic level we have measured various x-ray dichroisms at the Fe K-edge. The
results of these experiments carried out at the ESRF beamline ID12 on high quality
single crystals of GaFeO3 are presented here. Measurements of X-ray natural circular
dichroism originating from p-d hybridization at the Fe site in these nonenantiomorphous crystals confirmed that samples are untwined crystals. X-ray
magnetic circular dichroism spectra showed that there is a weak orbital magnetic
moment carried by 4p states of Fe and it is aligned antiparallel to the 3d spin moment.
X-ray magnetochiral dichroism and X-ray non-reciprocal magnetic linear dichroism
allowed us to disentangle experimentally the orbital anapole moment and higher order
magnetoelectric multipole moments carried by the Fe atoms in GaFeO3 crystals. All
these dichroisms are analyzed with the help of a set of the sum rules. This analysis
allowed us to deduce the expectation values of different effective operators related to
multiferroic properties of GaFeO3.
422
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High Temperature and Intrinsic Single-phase Bismuth Layerstructured Multiferroics
Jianlin Wang1, 2, Haoliang Huang2, 3, Zhengping Fu2, 3, 4, Yalin Lu1, 2, 3, 4, 5
1
Hefei 230026, P. R. China.
2
Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science
and Technology of China, Hefei 230026, P. R. China.
3
CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and
Engineering, University of Science and Technology of China, Hefei 230026, P. R. China.
4
Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and
5
Colorado 80840, USA.
Multiferroics are a kind of materials which simultaneously possess polarization
ordering and magnetic ordering. The conflicting requirements for d-obital electron
configurations of ferroelectricity and ferromagnetism result in the scarcity of
multiferroic materials. For a very long time, there is only one “star” multiferroic
material, BiFeO3 (BFO), which has the ferroelectric and magnetic transition
temperature above room temperature. In this study, we apply the magnetic layer
insertion method to synthesis a new multiferric material SrBi5Fe0.5Co0.5Ti4O18
(SBFCT). The remnant polarization and the remnant magnetization of SBFCT was 52.4
μC/cm2 and 2.24 emu/g, respectively, measured at room temperature. Especially, the
high temperature magneto-electric coupling effects of SBFCT were reached ~350
μV·cm-1·Oe-1 at 100 °C, which was so far the best result of all available high
temperature multiferroic ceramics reported. The magnetic field prototype senor we
manufactured using SBFCT works very well under low magnetic field at room
temperature. This makes multiferroic materials with the intrinsic magneto-electric
coupling effect attainable, which is essential to both fundamental research and device
application such as senor, information storage and quantum control.
Reference:
[1] J. F. Scott, NPG Asia Mater. 5: e72 (2013).
[2] X. Y. Mao, et al., Appl. Phys. Lett. 95: 082901 (2009).
[3] J. L. Wang, et al., Mater. Horiz. 2:232 (2015).
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Magnetoelectric coupling in mixed multiferroic state of
Eu1−x YxMnO3
A.Skaugen1, D. K. Shukla1,2, H. C. Walker1,3, S. Francoual1, J. Strempfer1
1
Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607 Hamburg, Germany
2
UGC DAE Consortium for Scientific Research, Khandwa Road, Indore 01, India
3
ISIS, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom
In the orthorhombic multiferroic systems, the role of the rare earth elements for
appearance of ferroelectric order is still being debated. Whereas TbMnO3 is
ferroelectric below TC=30 K, in GdMnO3 ferroelectricity appears in a very small
temperature range and is established in a wider temperature range only by an applied
external magnetic field. Investigation of the Gd magnetic order using resonant elastic
x-ray scattering (REXS) brings this in direct relationship to the order of Gd moments,
which is extended by application of magnetic field [1].
Deeper insight into the role of the rare earth is expected from the investigation of
Eu1-xYxMnO3, where Eu3+ (4f6) and Y3+ (4f0) ions both are in principle non-magnetic
[2,3]. A comparison of the magnetic order of the x=0.2 and 0.3 samples show different
ordering behaviour below the ferroelectric transition temperature TC=30 K [3]. In the
x=0.2 compound, the magnetic structure shows weak ferromagnetism, attributed to a
cone-like structure that breaks inversion symmetry and gives rise to ferroelectricity
with the polarization along the a-axis. High magnetic field measurements reveal a
stabilization of an intermediate canted spin structure, which is also responsible for an
increase in spontaneous polarization. The method of full polarization analysis has been
used to investigate different magnetic reflections at the Mn K-edge. From the
polarization scans the postulated magnetic order [4] is confirmed.
Reference:
[1] A. Skaugen et al., Journal of Physics: Conference Series 519, 012007 (2014)
[2] J. Hemberger et al., Phys. Rev. B 75, 035118 (2007)
[3] A. Skaugen et al., Phys. Rev. B 91, 180409 (2015)
[4] H. Jang et al. Phys. Rev. Letters 106, 047203 (2011)
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Magnetic structures and magnetoelastic coupling of Fe-doped
hexagonal manganites LuMn1-xFexO3 (0 ≤ x ≤ 0.3)
Zhendong Fu1,Yinguo Xiao2, Harikrishnan S. Nair3,Anatoliy Senyshyn4,5, Vladimir Y.
Pomjakushin6, Erxi Feng1, Yixi Su1, W. T. Jin1, Thomas Brückel2
1
Jülich Centre for Neutron Science JCNS at Heinz Maier-Leibnitz Zentrum MLZ,
Forschungszentrum Jülich GmbH, Lichtenbergstraße 1, D-85748 Garching, Germany
2
Jülich Centre for Neutron Science JCNS and Peter GrünbergInstitut PGI, JARA-FIT,
Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany
3
Highly Correlated Matter Research Group, Physics Department, University of Johannesburg P.
O. Box 524, Auckland Park 2006, South Africa
4
Institute for Material Science, Darmstadt University of Technology, D-64287 Darmstadt,
Germany
5
Forschungsneutronenquelle Heinz-Maier Leibnitz FRM-II, Technische Universität München,
Licthenbergstraße 1, D-85747 Garching b. München, Germany
6
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen PSI,
Switzerland
We have studied the crystal and magnetic structures of Fe -doped hexagonal
manganites LuMn1-xFex O3 (x = 0, 0.1, 0.2, and 0.3) by using bulk magnetization and
neutron powder diffraction methods. The samples crystalize consistently in a hexagonal
structure and maintain the space group P63cm from 2 to 300 K. The Néel temperature
TN increases continuously with increasing Fe-doping. In contrast to a single Γ4
representation in LuMnO3, the magnetic ground state of the Fe-doped samples can only
be described with a spin configuration described by a mixture of Γ3 (P63'cm') and Γ4
(P63'c'm) representations, whose contributions have been quantitatively estimated. The
ordered moment at base temperature amounts to about 3.2 to 3.5 μB per transition metal
ion, nearly independent of the doping ratio. The drastic effect of Fe -doping is
highlighted by composition-dependent spin reorientations. A phase diagram of the
entire composition series is proposed based on the present results and those reported in
literature. Our result demonstrates the importance of tailoring compositions in
increasing magnetic transition temperatures of multiferroic systems.
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Theory of Spin Wave Spin Current in Multiferroics
S. Miyhara
1Department of Applied Physics, Fukuoka University, Fukuoka, Japan
In magnetoelectric multiferroics, there is a strong coupling between magnetization
and electric polarization. Due to the magnetoelectric coupling, cross-correlated effects,
such as electric filed control of magnetization, appear prominently. Even in dynamical
processes, such a coupling induces novel effects. One of the examples is an electro
active magnon excitation, so-called electromagnon excitations [1]. In multiferroics,
several electro active spin wave modes can appear∙. For example, symmetryic spin-pair
dependent electricpolarization p =ΠSiSj can excite q= π spin wave mode in a cycloidal
screw spin structures [2,3]. In this way, electro active spin wave can have non-zero q
contrary to the conventional magnetic resonance modes and show the possibility for the
novel features as a spin-wave spin current.
Reference:
[1] H. Katsura, A.V. Balatsky, and N. Nagaosa, Phys. Rev. Lett. 98, 027203 (2007).
[2] R.Valdes Augilar et al. Phys. Rev. Lett 102, 047203 (2009).
[3] J.S. Lee et al., Phys. Rev. B 79, 180403 (2009).
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Mechanism of multiferroic properties formation in BaFe11.9D0.1O19
(D=Al; In) substituted M-type hexaferrites
A.V. Trukhanov1,2, S.V. Trukhanov2,V.G. Kostishin1, L.V. Panina1, V.A. Turchenko3
1Dep. Technology of electronic materials, NUST MISiS, Moscow, Russia
2Lab. of magnetic films physics, S&P materials research centre of NAS of Belarus, Minsk, Belarus
3Lab. of neutron physics, JINR, Dubna, Russia
In papers which demonstrate the multiferroic properties in M-type hexaferritesthere are too
much contradictory results about mechanisms: formation of non-collinear magnetic structures
(helical, conical, spiral, etc.)[1, 2] or noncentrosymmetry distortion of the oxygen octahedra
with collinear ordering of magnetic moments[3, 4].Dual ferroic properties (ferromagnetic and
ferroelectric ordering) were observed in BaFe11.9D0.1O19 (D=Al3+- BFAO, In3+- - BFIO) at room
temperatures. Consolidated magnetic moment is:BFAOat 300 K 9.75 µB/f.u.; BFIO at 300
K11.31 µB/f.u.The maximum polarization (Pmax), remanent polarization (Pr) and the coercive
electric field (EC) are:BFAO ~5.89 mC/m2, ~5.13 mC/m2and ~86 kV/m respectively;
BFIO~4.7mC/m2, ~3.8mC/m2and ~75 kV/m respectively.We estimated temperature
dependences (4.2-730K) of Fe-O bond lengths and Fe-O-Fe bond angles (main parameters that
determine the strength of superexchange interactions in complex oxides) by polarized neutrons
diffraction. All the Fe-O bond lengths (for Fe cations in different oxygen coordination) decrease
with temperature decreasing. The most changes in the bond lengths are detected for the Fe3O2 cation; for the Fe4-O5 and for the Fe5 - O2. Almost all from the bond angles decrease with
temperature decreasing except for the Fe3-O4-Fe5. Careful analysis of the unit model structure
suggests a perovskite-like crystal structure with one distorted FeO6 oxygen octahedron in
hexagonal BaFe11.9D0.1O19. In a normal octahedron, Fe cation is located at the center of an
octahedron of oxygen anions. However, in the unit cell of BaFe12-xDxO19 below the Curie
temperature, there is also a distortion to a lower-symmetry phase accompanied by the shift offcenter of the small Fe cation. Fe cation shifts away from the center along b-axis, while O5 and
O6 shift off their original positions of the octahedron along the opposite directions of a axis,
which leads to the distortion of O5–Fe–O6 bond away fromstraight line. The spontaneous
polarization derives, largely fromthe electric dipole moment, were created by the two shifts. So
neutron powder diffraction data (bond length and angels, collinear direction of magnetization
vector) indicate not only in which exactlyposition this iron cation is located – 12k position and
even preferable mechanism of multiferroic property formation (exchange-striction mechanism).
Acknowledgement The work was carried out with financial support in part from
theMinistry of Education and Science of the Russian Federation in the framework of
Increase Competitiveness Program of NUST «MISiS» (№ К4-2015-040).
References:
[1] Y. Tokunaga, et al., PRL, 105, 257201 (2010)
[2] A.M. Balbashov, etal., JETP Letters, 101, 489 (2015)
[3] V.G. Kostishynet al.,JMMM,400, 327 (2016)
[4] G. Tan, X. Chen, JMMM,327 87 (2013)
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Change in crystal structure and physical properties of the
Multiferroics YMnO3 single crystal by Strong gravitational field
Makoto Tokuda1, Ma Weijian1, Shinya Hayami2, Tadao Nishiyama2, Akira Yoshiasa2,
andTsutomu Mashimo1
1
Institute of Pulsed Power Science, Kumamoto University, Kumamoto, Japan
2
Faculty of Science, Kumamoto University, Kumamoto, Japan
Many researchers have studied the multiferroicity of the hexagonal RMnO3 (R: rareearth element) for both applications and fundamental studies. To investigate the
relationship between the structure and physical properties of materials, some people
apply the chemical pressure effect. The procedure of chemical pressure effect involves
substituting rare-earth elements for ones which have a different ionic radius. Mashimo
et al. have developed a high-temperature ultracentrifuge apparatus that can generate
extended duration strong gravitational field in excess of 106 G under a wide range of
temperatures (up to 500°C). Strong gravitational fields directly act on each atom as a
different body force. This can cause the change in crystal structure. Thus, we subjected
YMnO3 single crystal to strong gravity experiments (0.78×106 G, 400°C, 2 h) and
investigated the resulting changes in the crystal structure and physical properties of the
gravity sample. The single crystal four-circle X-ray diffraction measurements revealed
the change in the nearest neighboring Mn-Mn and M-O bond distances. The
temperature dependence of magnetic susceptibility by SQUID showed the change in
the magnetic anisotropy of gravity sample.
Reference:
[1]T. Mashimo, et al., Rev. Sci. Instr, 67, 3170 (1996)
[2]T. Mashimo, et al., J. Appl. Phys. 90, 741-744 (2001)
[3]T. Katsufuji, et al., Phys. Rev. B 64, 104419 (2001)
[4]J. Park, et al., Phys. Rev. B 82, 054428 (2010)
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Valence Transition in Negative Thermal Expansion Material BiNiO3
Makoto Naka1, Hitoshi Seo2, and Yukitoshi Motome3
1
2
Department of Physics, Tohoku University, Sendai, Japan
Condensed Matter Theory Laboratory and CEMS, RIKEN, Wako, Japan
3
Department of Applied Physics, University of Tokyo, Tokyo, Japan
We theoretically study [1] the metal-insulator transition in transition metal oxide
BiNiO3 where colossal negative thermal expansion is observed [2]. The transition is
accompanied by a charge transfer between the Bi and Ni sites; i.e. a valence transition.
We introduce an effective two-component electronic model for the Bi-6s and Ni-3d
orbitals, taking into account the valence skipping of the Bi cation. A notable feature is
that the electronic state of the usually inert “A-site” in the perovskite-type structure
is now explicitly incorporated. We investigate the ground-state and finite-temperature
properties of this model within the mean-field approximation.
We find that the valence transition indeed occurs in our model which captures the
essence of the experiments. Namely, the charge transfer triggers a bipolaronic charge
ordering in the Bi sites owing to its valence skipping nature, and at the same time the
Ni sites become half-filled and then unstable toward magnetic ordering (Mott
insulating). Our results indicate that the instability can be considered as a
commensurate locking of the electron filling in each orbital toward such orderings. The
mean-field phase diagram (see Figure) by varying the relative energy between the Bi
and Ni levels well explains the experiments: not only the temperature- and pressuredriven transition producing the negative thermal expansion in BiNiO3, but also the
systematic variation of valence states for a series of perovskite oxides BiMO3 and
PbMO3 (M: transition metals). Our work can serve as a guideline for searching new
functional materials.
Figure: Global phase diagram of the two-component model for BiNiO3 [1]. UB and ∆ are the onsite Coulomb interaction (allowing attraction) for Bi sites and relative energy between Bi and Ni
sites, respectively. CO and AFM stand for charge and antiferromagnetic orders.
Reference:
[1] M. Naka, H. Seo, and Y. Motome, to be published in Phys. Rev. Lett.
[2] M. Azuma et al., Nat. Commun. 2, 347 (2011).
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Oxygen Vacancies Effects in Eu0.5 Ba0.5 TiO3−𝛿 Multiferroic Thin
Films
Hao Yang1, Sheng Ju2, Albina Borisevich3, Kuijuan Jin4, Yuheng Zhang5
1
College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China
2
College of Physics, Optoelectronics and Energy, Soochow University, Suzhou 215006, China
3
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge,
4
Academy of Science, Beijing 100190, China
5
High Magnetic Field Laboratory, Chinese Academy of Science, Hefei 230031, China
E-mail:[email protected]
Oxygen vacancies (VO) in complex oxides offer an extra functionality dimension via
their strong coupling with lattice and electronic structure of the material. Developments
of electron microscopy techniques and density functional theory (DFT) have led to
recent discoveries of VO induced new properties such as polar behavior in
(LaFeO3)2/SrFeO3 superlattices, and ferromagnetism in strained LaCoO3-δ thin
films. Controlling the VO during material synthesis thus become a promising route for
creating novel multiferroic materials.
In this work, VO effects on the multiferroic behavior in Eu0.5Ba0.5TiO3-δ thin films
have been investigated using a combination of experimental measurements and firstprinciples calculations. Eu0.5Ba0.5TiO3 ceramics have been known to exhibit
antiferromagnetic (TN = 1.9 K) and ferroelectric
(TC
= 213 K) properties.
While, Eu0.5Ba0.5TiO3-δ thin films show
ferromagtic-ferroelectric
(FM-FE)
properties and, for the highest concentration of VO (i.e. δ >0.04), the ferroelectric Curie
temperature is above room temperature. Considering the easy formation of VO, our
work presents a new methodology to realize the coexistence of FM-FE orders in oxide
thin films.
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Control of electronic phases & charge transport in hole doped
manganite by electrostatic carrier modulation
Rajib Nath 1 ,A. K Raychaudhuri1
1
Dept. of Condensed matter physics & Material sciences, S. N. Bose National Centre for Basic
Sciences, Kolkata, India.
Email:[email protected]
The magnetite system especially La1-xCaxMnO3 shows coexistence of different
electronic phases when the parent system LaMnO3 doped by divalent atoms at the rare
earth position. Chemical doping generally introduces structural disorder as well as
electronic inhomogenities in the system in an irreversible way which make it difficult
to understand their intrinsic electronic properties. Other than chemical doping,
electrostatic carrier doping can play a crucial role to perturb the electronic properties as
well as electronic phase in manganites without creating any kind of disorder. The
bipolar control of co-existing electronic phases in a hole doped manganite (La 0.85Ca
0.15MnO3) film can be achieved by electrostatic carrier modulation using an applied gate
bias in a field effect (FE) device configuration. The gate induced field affects the
transport within the grain (intra grain) as well as inter-grain transport by controlling the
depletion layer and the potential barrier at the grain boundaries. We observed a large
modulation in the resistance of the film, ±40%, at room temperature for a moderate
gate bias (VG) of 4V, which increased to ±100% at 100K. The field-effect-induced
charges alter the relative fraction of the coexisting phases as well as the characteristic
temperatures, such as the orthorhombic–orthorhombic (O–O/) transition temperature,
the ferromagnetic transition temperature, and the onset temperature of the low
temperature FMI state. We found that Electrostatic carrier modulation affects the
electronic transport in this hole doped perovskite oxide system as the same way divalent
atom substitution by chemical method or chemical doping does. There are many future
prospects of electrostatic carrier modulation by EDL which can be used to study the
electronic phenomena of strongly correlated oxides and other functional oxides.
Reference:
[1] Rajib Nath et al., RSC Advances 5, 57875 (2015)
[2] Rajib Nath et al., Appl. Phys. Lett. 104, 083515 (2014)
431
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Spin wave and Electromagnon Dispersions in Multiferroic MnWO4
as Observed by Neutron Spectroscopy
Y. Xiao1, C. M. N. Kumar2, 3, S. Nandi1, 4, Y. Su4, W.T. Jin1, 4, Z. Fu4, E. Faulhaber5,
A. Schneidewind4, 5, and Th. Brückel1, 4
1
Jülich Centre for Neutron Science JCNS and Peter Grünberg Institut PGI, JARA-FIT,
Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
2
Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Outstation at SNS,
POB 2008, 1 Bethel Valley Rd. Oak Ridge, TN 37831-6473, USA
3
Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge,
4
Jülich Centre for Neutron Science JCNS at Heinz Maier-Leibnitz Zentrum, Forschungszentrum
Jülich GmbH, Lichtenbergstraße 1, 85747 Garching, Germany
5
Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM-II), TU München, 85747 Garching,
Germany
High resolution inelastic neutron scattering reveals that the elementary magnetic
excitations in multiferroic MnWO4 consist of low energy dispersive electromagnons in
addition to the well-known spin-wave excitations. The latter can well be modeled by a
Heisenberg Hamiltonian with magnetic exchange coupling extending to the 12th nearest
neighbor. They exhibit a spin wave gap of 0.61(1) meV. Two electromagnon branches
appear at lower energies of 0.07(1) meV and 0.45(1) meV at the zone center. They
reflect the dynamic magnetoelectric coupling and persist in both, the collinear magnetic
and paraelectric AF1 phase, and the spin spiral ferroelectric AF2 phase. These
excitations are associated with the Dzyaloshinskii-Moriya exchange interaction, which
is significant due to the rather large spin-orbit coupling.
Reference:
[1] C. M. N. Kumar, et al., PRB 91, 235149 (2015).
[2] Y. Xiao et al., to be published.
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Orbital degenerated 3d1 system α-Sr2VO4 investigated by 51V NMR
Yusuke Kato,1 Yasuhiro Shimizu,1 Yoshiaki Kobayashi,1 Masayuki Itoh,1 Hiroya
Sakurai,2 Ting-Hui Kao,2, 3 and Hung-Duen Yang3
1
Department of Physics, Nagoya University, Nagoya, Japan
2
National Institute for Materials Science, Tsukuba, Japan
3
Department of Physics, National Sun Yat-Sen University, Kaohsiung, Taiwan
In d electron systems with degenerated orbitals, a novel ground state such as orbital
liquid and multipole order has been discussed particularly from theoretical point of
view. One candidate of such systems is α-Sr2VO4, a 3d1 system with the degenerated
dxy/dyz orbital due to the tetragonal crystal field. This oxide was reported to undergo
successive phase transitions with structural changes at 120 and 100 K. Models of stripetype orbital and spin order [1] and magnetic octapole order [2] were proposed as its
ground state. However, the ground state and the phase transitions have not been
uncovered in spite of intensive experimental studies. We report the 51V NMR results of
α-Sr2VO4, the temperature dependences of the NMR spectrum, the Knight shift and the
nuclear spin-lattice relaxation rate, and discuss the ground state and the phase
transitions with the structural data reported.
References:
[1] Y. Imai et al., PRL 95, 176405 ( 2005 )
[2] G. Jackeli et al., PRL 103, 067205 ( 2009 )
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Magnetic Resonance and optical Study on the Orbital Order in
Ba3CuSb2O9
Y. Han1, M. Hagiwara2, T. Nakano3, Y. Nozue3, K. Kimura4, M. Halim4, S.
Nakatsuji4, N. Katayama5, and H. Sawa5.
1
Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of
Science and Technology, Wuhan, China.
2
Center for Advanced High Magnetic Field Science, Graduate School of Science, Osaka
University, Osaka, Japan.
3
Graduate School of Science, Osaka University, Osaka, Japan.
4
Institute for Solid State Physics, University of Tokyo, Chiba, Japan.
5Department of Applied Physics, Nagoya University, Nagoya, Japan.
Orbital order plays an important role in the electronic and magnetic structure of
condensed matter with Jahn-Teller effect, but mostly it undergoes an ordered state as
the strong exchange interactions. Here we report a novel compound Ba3CuSb2O9
(BCSO) shows different orbital orders as the stoichiometry of Cu and Sb changes [1-3].
We used two techniques – the electron spin resonance and magneto-optical absorption
spectra to measure two BCSO single crystals with and without static Jahn-Teller
distortion, and observe direct evidence of an orbital liquid state in the stoichiometric
single crystal.
Reference:
[1] Y. Han et al., PRB 114, 146403 (2015).
[2] N. Katayama et al., PNAS 112, 9305 (2015).
[3] S. Nakatsuji et al., Science 336, 559 (2012)
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V-NMR study of charge order induced by cation order in δAg2/3V2O5
Y. Kawasaki1, R. Morioka1, Y. Kishimoto1, K. Nakamura1, K. Nishiyama2, T. Koyama2, T.
Mito2, T. Baba3, T.Yamauchi3, M. Isobe4, Y. Ueda5
1
Institute of Technology and Science, Tokushima University, Tokushima, Japan
2
Graduate School of Material Science, University of Hyogo, Hyogo, Japan
3
4
Max-Planck Institute, Stuttgart, Germany
5
Toyota Physical and Chemical Research Institute, Aichi Nagakute, Japan
Several compounds of vanadium bronze have drawn much interest as a stage of
various quantum phenomena. In this study, the δ-phase of vanadium bronze has been
investigated by using 51V-NMR methods, focusing on δ-Ag2/3V2O5 which shows the
novel V4+/V5+ charge order induced by the Ag ions order at around 220 K [1, 2]. It has
been clarified that the ground state of this material is a charge ordered one with a spin
singlet of 3d electrons on V4+-V4+ pair from a microscopic point of view. When the
sample is rapidly cooled down from room temperature, which may prevent the Ag ions
order, the majority of 3d electrons remain paramagnetic without forming a spin singlet.
These results indicate that the geometrical arrangement of magnetic V4+ ions required
for the spin-singlet state is closely related to the Ag ions order.
Reference:
[1] T. Baba et al., J. Phys. Soc. Jpn. 84, 024718 (2015)
[2] Y. Kawasaki et al., J. Phys.: Conf. Ser. 592, 012042 (2015)
435
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Entanglement and magnetism in graphene nanoribbons
Imre Hagymási1, Levente Tapasztó2, Örs Legeza1
1
Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, PO Box 49, H1525 Budapest, Hungary
2
Institute of Technical Physics and Materials Science, Centre for Energy Research, PO Box
49, H-1525 Budapest, Hungary
In the first part of the work we performed electronic structure and magnetic ordering
calculations on graphene nanoribbons by applying the mean-field theory for an
extended Hubbard Hamiltonian including the effect of temperature and finite doping.
We found that ribbons with zigzag edge orientation possess spin polarized edge states
with both antiferromagnetic (AF) and ferromagnetic (FM) coupling between opposite
edges. The calculations revealed a strong connection between the electronic and
magnetic properties of zigzag graphene nanoribbons, AF ribbons displaying
semiconducting, while FM ribbons showing metallic behavior in excellent agreement
with our experimental findings [1].
In the second part, we applied the density-matrix renormalization group (DMRG)
algorithm to go beyond the single-particle description, and determined the ground state
of finite graphene ribbons with various edge configurations keeping block states up to
20000. Using the elements of quantum information theory, we calculated the
entanglement patterns between the carbon atoms, which reveal the intrinsic properties
of the true many-body ground state. [2]
Reference:
[1] G. Zs. Magda, et al., Nature 514, 608-611 (2014).
[2] I. Hagymási, Ö. Legeza, in preparation
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Orbital Magnetism of Bloch Electrons Applied to Single-Band
Models and Graphene
Masao Ogata1
1
Department of Physics, University of Tokyo, Hongo, Bunkyo-ku Tokyo, Japan
Recently we have derived an exact formula of orbital susceptibility expressed in
terms of Bloch wave functions [1] starting from the exact one-line formula by
Fukuyama written in terms of Green's functions. The obtained formula contains four
contributions: (1) Landau- Peierls susceptibility, (2) interband contribution, (3) Fermi
surface contribution, and (4) contribution from occupied states which we call intraband atomic diamagnetism. Except for the Landau-Peierls susceptibility, the other
contributions involve the crystal-momentum derivatives of Bloch wave functions. The
present formula is simplified compared with those obtained previously by Hebborn et
al.
Based on this formula, the band effects are studied in terms of linear combination of
atomic orbital treating overlap integrals between neighboring atomic orbitals as a
perturbation. The orbital susceptibilities of single-band models in two-dimensional
square and triangular lattices and of a two-band model for graphene are calculated
exactly up to the first-order with respect to the overlap integrals. In addition to the
Landau-Peierls susceptibility, it is found that there are comparable contributions from
the Fermi surface and from the occupied states in the partially-filled band. In the case
of graphene (or honeycomb lattice), there also appear interband contributions between
the upper and lower massless Dirac cone, which have not been included in the previous
calculations. The obtained results are compared with those obtained by using the Peierls
phase in the tight-binding models. This result means that the Peierls phase is not enough
as the effect of magnetic field.
Reference:
[1] M. Ogata and H. Fukuyama, J. Phys. Soc. Japan 84, 124708 (2015).
437
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Friedel oscillation near a van Hove singularity in two-dimensional
Dirac materials
Dr. Chi-Ken Lu1
1
Physics Department, National Taiwan Normal University, Taipei, Taiwan
We consider Friedel oscillation in the two-dimensional Dirac materials when Fermi
level is near the van Hove singularity. Twisted graphene bilayer and the surface state
of topological crystalline insulator are the representative materials which show lowenergy saddle points that are feasible to probe by gating. We approximate the Fermi
surface near saddle point with a hyperbola and calculate the static Lindhard response
function. Employing a theorem of Lighthill, the induced charge density $\delta n $ due
to an impurity is obtained and the algebraic decay of $\delta n$ is determined by the
singularity of the static response function. Although a hyperbolic Fermi surface is rather
different from a circular one, the static Lindhard response function in the present case
shows a singularity similar with the response function associated with circular Fermi
surface, which leads to the $\delta n\propto R^{-2}$ at large distance $R$. The
dependences of charge density on the Fermi energy are different. Consequently, it is
possible to observe in twisted graphene bilayer the evolution that $\delta n\propto R^{3} $ near Dirac point changes to $\delta n\propto R^{-2}$ above the saddle point.
Measurements using scanning tunnelling microscopy around the impurity sites could
verify the prediction.
Reference:
[1] arXiv:1601.00801 (accepted by Journal of Physics: Condensed Matter)
438
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Giant frequency tuneability enabled by external magnetic field in
active graphene metamaterials
Xiang Hu1, Qiuping Huang1, and Yalin Lu1, 2
1
Advanced Applied Research Center, Hefei National Laboratory for Physical Sciences at the
Microscale, University of Science and Technology of China, Hefei, Anhui, 230026, P. R.
China;
2
Colorado 80840, USA
Metamaterials plays enormous roles in manipulating electromagnetic waves by
providing unique features that cannot be obtained with natural materials [1]. Especially,
the electromagnetic behavior of metamaterials can be drastically enhanced by dynamic
control through incorporation of active media [2]. A remarkable example is a graphene
metamaterial – an integration of graphene with a planar metasurface, where the
metamaterial is endowed with the unique optical and electronic properties of graphene,
resulting in intriguing possibilities in electromagnetic wave control [3]. Here, through
a combination of external magnetic field and gate electric field, we demonstrate an
unprecedented six-channel modulation of terahertz waves in a graphene metamaterial
[Fig.1(a)]. Moreover, ultra-high modulation efficiency is found solid at the edge of
transition between Landau levels [Fig.1(b)]. Underlying mechanism is carried out using
full quantum mechanical interpretation of graphene. Such excellent frequency
tuneability and gate control ability of graphene metamaterial opens up prosperous
prospects for its applications in various realms like spin optics, active optoelectronics,
ultrafast optics, and etc.
Fig.1. (a) Mapping of the modulation depth spectrum with varying magnetic field B; red areas
indicate six modulation channels in total; dashed lines indicate the corresponding Landau level
transitions. (b) Reflection spectrum tuned by Fermi level EF; the required variation on EF is as low
as 10 meV.
References:
[1] Valentine Jason et al., Nature 455, 7211, 376-379 (2008).
[2] Hou-Tong Chen et al., Nature 444, 7119, 507-600 (2006).
[3] Quan Li et al., Nature Comms 6, 7082 (2015).
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