L`effet de désordre sur les propriétés des

L'effet de désordre sur les propriétés des supraconducteurs à base de fer Marcin Konczykowski, Laboratoire des Solides Irradiés Ecole Polytechnique, Palaiseau, France Collaborateurs: C.J. van der Beek (LSI) Ruslan Prozorov, Ames Laboratory, Iowa State University, USA Takasada Shibauchi, Yuta Muzakami, Shibaru Kasahara, Yuji Matsuda, Kyoto University, Japan Samples Ba(FeAs1-­‐xPx)2: Shibaru Kasahara, Kyoto University, Japan LiFeAs: Kee Hoon Kim, Seoul NaRonal University, Seoul, Korea BaK(FeAs)2: Hai-­‐Hu Wen, Nanjing University, Nanjing, P. R. China Sr(FeAs1-­‐xPx)2, Ba(Fe1-­‐x,RuxAs)2: Paul C. Canfield, The Ames Laboratory, USA •  FeSeTe: Zhiqiang Mao, Tulane University, New Orleans, USA • 
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Hall arrays: Vincent Mosser, ITRON, Issy-­‐les-­‐Moulineaux, France IrradiaRons: electrons: SIRIUS plaZorm Ecole Polytechnique swi\ heavy ions: GANIL (Caen) Disorder in superconductors Outline Flux pinning: As grown samples: SuperposiRon of strong pinning from nanometer scale defects and of weak collecRve pinning from charged defects. Irradiated materials: Columnar defects, Bose glass type of pinning. Pairbraking: No effect from large (columnar defects)
Strong depression of Tc, increase of resisRvity and modificaRon of superconducRng gap structure by point defects. ImplicaRon for pairing mechanism. Two types of irradiaRon induced disorder Swi\ heavy ions: typically 5.8 GeV Pb Columnar amorphous tracks few nanometers diameter Strong pinning for H// tracks Electron irradiaRon 2.5 MeV of samples cooled to 20K. CreaRon of stable Frenkel pairs on all sub-­‐laeces ParRal recombinaRon of defects on warming but final state: uniform spread of point defects Defauts crées par irradiaRon SIRIUS plaZorm NEC Pelltron accelerator Target at low temperature (20K liquid hydrogen) to prevent defect migraRon electron beam energy from 0.3 to 2.5 MeV In-­‐situ measurements: resisRvity (operaRng, AC Hall in progress) Magnetometry using 2D Electron Gas Hall sensor gradiometer • 
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Pseudomorphic AlGaAs/InGaAs/GaAs heterostructure Passivated, ion implantaRon delimited line of 10 sensors Sensor size 3x3µm2 each, spaced by 10µm or 20µm Constant sensiRvity 80mΩ/Gauss (from milliK to RT). SpaRally resolved measurement of the local flux density B e.g single crystal Ba(Fe0.76Ru0.24As0.64)2 cut to rectangle Local gradient dB/dx vs. local inducRon B isothermal loops j = 2 dB µ0 dx 1G/µm=16000 A/cm2 Magnetometry u
sing 2
D E
lectron G
as AC mode Hall sensor in AC mode AC generator 2DEG GaAlAs Hall sensor
H
Lock-­‐in detector Current source T’= B’AC/HAC can be converted to screening current
Jc=1/π arccos(2T’-1)
Onset of T’3H marks nonlinear I-V used to
determine IRL
Gilchrist & Konczykowski Physica C 212, 43 (1993)
Disorder in prisRne material: two origins of pinning Low field, central peak “Strong pinning”, nm scale fluctuaRon of Tc High field “weak collecRve pining” by charged defects npξ3 >> 1
jc = Fp/B determined by <fp2> niξ3<<1
jc = ni u02 fp/Φ0 direct sum of the fp Yu. Ovchinnikov and B. Ivlev, Phys. Rev. B 43, 8024 (1991)
C.J. van der Beek et al., PRL 105, 267002 (2010) PRB 81, 174517 (2010).
A.I. Larkin and Yu. Ovchinnikov, JETP 31, 784 (1970); J. Low. Temp. Phys. 34, 409 (1979) ExcepRon: isovalently subsRtuted Ba(FeAs1-­‐xPx)2 No signature of “weak collecRve pinning” regime Controlled disorder: columnar defects Heavy ion irradiaRon: columnar defects, strong enhancement of pinning asenuate or erase central peak => field independent Jc Controlled disorder Heavy ion irradiaRon: columnar defects, strong enhancement of pinning asenuate or erase central peak => field independent Jc FeSe Te
1-x
8
4.2
6
8
10
2
4
0
-2
2
0
-2
-4
-6
-4
-8
-4000
-2000
0
B [G]
2000
4000
T[K]
4.2
7
8
9
10
11
12
13
14
6
T[K]
4
dB/dx [G/!m]
!
dB/dx [G/!m]
x
FeSeTe 47% irradiated 1GeV Xe, B =4T
x=0.47 crystal H//c pristine
-2000
-1000
0
B [G]
1000
2000
Controlled disorder: columnar defects Columnar defects: Proof from anisotropy of pining But small diameter and unstable (annealing at room temperature) Pronounced flux creep: ≈ 5% Rme decade with U(J) ≈(Jc/J)µ . Persist a\er irradiaRon with change of regime fromµ =0.5-­‐1 in prisRne samples (vortex loop nucleaRon) µ=0.3 in ion irradiated irradiated samples (variable range hopping) Columnar defects: IRL & Tc Heavy ion irradiaRon: enhancement of pinning without depression of Tc Isovalently subsRtuted Ba(FeAs1-­‐xPx)2: no measurable change of IRL, other compounds slight upward shi\ of IRL Ba(FeAs1-­‐xPx)2 & Ba(Fe1-­‐xRuxAs)2 point disorder As Ba(Fe Ru As) x=0.24 crystal#2
1-x
x
2
IRL H//c at 11Hz before and after e- irradiation
Strong depression of Tc By point like disorder Linear with irradiaRon dose Down to <50% of iniRal Tc 30000
irradiated
19
1.7x10
pristine
25000
-
e /cm
2
Ba(Fe Ru As) x=0.24
15000
1-x
x
2
irradiated with 2.5 MeV electrons at 20K
0
10000
Faster than in HTC cuprates -0.5
5000
-1
8
9
10
11
T [K]
12
13
14
c
0
!T [K]
H[Oe]
20000
-1.5
Strong depression in all compounds except FeSeTe -2
-2.5
-3
0
0.5
1
1.5
2
2
dose [C/cm ]
2.5
3
Ba(Fe1-­‐xRuxAs)2 resisRvity point disorder As Ba(FeAs1-­‐xPx)2 point disorder As DeterminaRon of scasering rate from resisRvity: problem: semi metallic two band conducRvity Hall coefficient does not reflect carrier concentraRon. Need high magneRc field to separate hole and electron contribuRon. Change in Rh(T) variaRon a\er irradiaRon indicate charge redistribuRon. Experimental observation of node lifting by disorder
CONCLUSIONS DisRnct effects of different types of disorder on pinning and paibraking -­‐  Large defects (columnar) : interband scasering lisle effect on Tc -­‐  Point defects: intraband scasering: strong pairbraking effect. -­‐  Suppression of nodes in superconducRng gap by disorder incompaRble with symmetry induced nodes (d-­‐wave) -­‐ EvoluRon of gap structure with disorder compaRble with S+/-­‐ coupling