Presentation

Electron Transport in/across
the van der Waals Interfaces
Philip Kim
Physics Department, Harvard University
Acknowledgement
Amelia Barreiro, Dmitri Efetov, Cheol Ho Lee, Austin Fong, Patrick Maher,
Wei Tsen, Xiaomeng Xue
Collaborators
Collaborators:
Current Members
Collaborating Students/postodcs
Horst Stormer, Aron Pinczuk, Tony Heinz, Abhay
Yue Zhao
Cory Dean, Inanc Meric, Lei Wang,
Jim
Hone,
Ken
Shepard,
Tony
Heinz,
Cory
Dean
(Columbia),
Jing Guo (UF)
Pasupathy, Latha Venkataraman
Mitsuhide Takekoshi
Sebastian Sorgenfrei, Kevin Knox, Nayung
Louis Brus, George Flynn, Colin Nuckolls,
Andrea
Jung, Seok
Ju Kang, Jun Yan,
YanwenWatanabe
Tan,
G.
C.Young
Yi (SNU), Takashi
Taniguchi,
Kenji
(NIMS)
Jim
Hone, Ken Shepard, Louis Campos, Rick Osgood
Dmitri Efetov
Kevin Knox
Fereshte Ghahari
Patrick Maher
Young-Jun Yu (jointly with GRL, POSTECH)
Vikram Deshpande (jointly with Hone group)
Paul Cadden-Zimansky (Columbia Frontier of Science Fellow)
Chenguang Lu (jointly with Hone and Herman
T. Taniguchi, K, Watanabe
Andre Geim, Kostya Novoselov, Sanka Das Sarma
Past Members
Melinda Han (Ph.D. 2010, Frontier of Science Fellow, Columbia University)
Meninder S. Purewal (Ph.D. 2008)
Josh Small (Ph.D. 2006)
Yuanbo Zhang (Ph.D. 2006, Professor, Fundan University)
Yuri Zuev (Ph.D. 2011, IBM Fishkill)
Kirill Bolotin (Assistant Professor, Department of Physics, Vanderbilt University)
Byung Hee Hong (Associate Professor, Department of Chemistry, Seoul National University)
Pablo Jarillo-Herrero (Assistant Professor, Department of Physics, MIT)
Kim
Keunsoo Kim (Assistant Professor, Department of Physics, Sejong University)
Namdong Kim (Research Scientist, POSTECH)
Barbaros Oezyilmaz (Assistant Professor, Department of Physics, National University of Singapore)
Funding:
group and friends (2011)
Pick-up Technique and Edge Contacts
for Multilayer vdW Stacking (Columbia Team)
• 
Creation of multilayer
systems with colamination techniques
• 
Encapsulated
graphene in hBN
• 
Completely ballistic at
low temperature
Edge contacting method
Contac Resistance: 100 Ω µm
Mobility ~ 106 cm2/Vsec
Mean free path > 10 µm
L. Wang et al, Science (2013)
Magnetic Focusing in Graphene
(collaboration with Cory Dean)
L = 7.5 µm
L = 15 µm
Similar result in Taychatanapat et al. (2013) Fractional Quantum Hall Effect in Moire Superlattice
Single layer graphene on hBN @ 20 mK up to 35 T
Hall Conductivity
Fractional Quantum Hall Effect
-1
σxy (mS)
0
1
Rxx
Rxy
2/3
B (T)
4/3
5/3
7/3
Vg (V)
•  Fractal quantum Hall effect due to the periodic
electric potential form graphene/hBN moire.
4/3 5/3
7/3
8/3
10/3 13/3
(ν)
σxx (e2/h)
•  Competition between fractional and fractal
quantum Hall effect in the extreme quantum
condition.
In collaboration with C. Dean (Columbia)
Noise Thermometry and Hydrodynamic Transport
Johnson noise thermometry
5 µm
hBN encapsulated
graphene with low
inhomogeneity
Crossno et al. (2015)
Breakdown of Wiedeman Franz law
Enhancement of electric contribution of thermal transport at charge neutrality due to hydrodynamic transport
Effect of CDW Dimensionality: Thin TaS2
Electrical transport in
encapsulated TaS2
Encapsulated TaS2 on SiN membrane for TEM study
Electron diffraction from TEM
•  Nearly commensurate to
commensurate CDW
phase transition is
suppressed due to
increasing disorder
contribution in thin
samples.
•  CDW phase transition can
be modulated by current
Tsen et al (2015)
(Collaboration with Pasupathy group)
Andreev Reflections – between NbSe2 & Graphene
Efetov et al. (2015) graphene
5 µm
NbSe2
Tc = 7 K
Hc2 = 4.5 T
Graphen Hall-bar
With NbSe2 as a current
injection electrode
Andreev reflection
between graphene
and NbSe2 across
vdW interface
Gate Depedent Andreev Reflections
– Sign of Specular Andreev Reflection
Efetov et al. (2015) Normal AR (EF > Δ)
Specular AR (EF < Δ)
Inter valley AR (eV > EF)
Intra valley AR (eV < EF)
Atomically Thin PN junction: MoS2/WSe2
Vertical & Lateral Channels
W2
WSe2
M1
W1
MoS2
J. A. =8.8 µm2
- Al contact to MoS2 for electron injection
- Pd contact to WSe2 for hole injection
10
-5
10
-6
10
-7
10
-8
10
-9
10
-10
10
-11
10
-12
-60
0.1
Illumination
Dark
Vds = 0.5 V
WSe2 p-type
MoS2 n-type
I (nA)
Ids (A)
-4
M2
M3
PN diode characteristics
Field Effect Transistor Characteristics
10
5 µm
Active
zone
0
Off
Off
-0.1
-0.5
-40
VgVg
(V)(V)
2020
1010
00
-10
-10
-20
-20
-20
0
Vg (V)
20
40
60
0.0
0.5
1.0
Vds
(V)
ds
Atomically thin tunable photovoltaic cell!
C. Lee et al. Nature Nano (2014) Electric Field Effect Tunable PL: MoS2/WSe2
Van der Waal Heterostructures Graphene (semimetal) Graphene hBN MoS2 WSe2 NbSe2 TaS2 Cr2Ge2Te6 Bi2Se3 Twisted stacking Hofstadter BuAerfly; tunneling SchoAky diode SchoAky diode Andreev reflecFon Super laGce potenFal MagneFc insulaFng ContacFng surface states Twisted stacking EncapsulaFon EncapsulaFon EncapsulaFon, tunneling EncapsulaFng, tunneling Control exchange interacFon EncapsulaFng, tunneling Twisted stacking Atomic pn juncFon Supercond /
Semicond junFon Super laGce modulaFon MagneFc semiconductor Valley tronics Twisted stacking Supercond /
Semicond junFon Super laGce modulaFon MagneFc semiconductor Valley tronics Josephson coupling CompeFng order parameters Triplet superconductor Majorana C-­‐axis CDW orders CompeFng order parameters Super laGce modulaFon C-­‐axis magneFc orders CreaFng gap in TI surface hBN (insulator) MoS2 (n-­‐semicond) WSe2 (p-­‐semicond) NbSe2 (supercond.) TaS2 (CDW) Cr2Ge2Te6 (magneFc) AnnihilaFon of TI surface states Bi2Se3 (T. I.) performed in-­‐progress Planned Acknowledgement
Amelia Barreiro, Dmitri Efetov, Cheol Ho Lee, Austin Fong, Patrick Maher,
Wei Tsen, Xiaomeng Xue
Collaborators
Collaborators:
Current Members
Collaborating Students/postodcs
Horst Stormer, Aron Pinczuk, Tony Heinz, Abhay
Yue Zhao
Cory Dean, Inanc Meric, Lei Wang,
Jim
Hone,
Ken
Shepard,
Tony
Heinz,
Cory
Dean
(Columbia),
Jing Guo (UF)
Pasupathy, Latha Venkataraman
Mitsuhide Takekoshi
Sebastian Sorgenfrei, Kevin Knox, Nayung
Louis Brus, George Flynn, Colin Nuckolls,
Andrea
Jung, Seok
Ju Kang, Jun Yan,
YanwenWatanabe
Tan,
G.
C.Young
Yi (SNU), Takashi
Taniguchi,
Kenji
(NIMS)
Jim
Hone, Ken Shepard, Louis Campos, Rick Osgood
Dmitri Efetov
Kevin Knox
Fereshte Ghahari
Patrick Maher
Young-Jun Yu (jointly with GRL, POSTECH)
Vikram Deshpande (jointly with Hone group)
Paul Cadden-Zimansky (Columbia Frontier of Science Fellow)
Chenguang Lu (jointly with Hone and Herman
T. Taniguchi, K, Watanabe
Andre Geim, Kostya Novoselov, Sanka Das Sarma
Past Members
Melinda Han (Ph.D. 2010, Frontier of Science Fellow, Columbia University)
Meninder S. Purewal (Ph.D. 2008)
Josh Small (Ph.D. 2006)
Yuanbo Zhang (Ph.D. 2006, Professor, Fundan University)
Yuri Zuev (Ph.D. 2011, IBM Fishkill)
Kirill Bolotin (Assistant Professor, Department of Physics, Vanderbilt University)
Byung Hee Hong (Associate Professor, Department of Chemistry, Seoul National University)
Pablo Jarillo-Herrero (Assistant Professor, Department of Physics, MIT)
Kim
Keunsoo Kim (Assistant Professor, Department of Physics, Sejong University)
Namdong Kim (Research Scientist, POSTECH)
Barbaros Oezyilmaz (Assistant Professor, Department of Physics, National University of Singapore)
Funding:
group and friends (2011)