S. Haddad LPMC, Département de Physique, Faculté des Sciences de Tunis, Tunisia S. Charfi-Kaddour
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Transcript of S. Haddad LPMC, Département de Physique, Faculté des Sciences de Tunis, Tunisia S. Charfi-Kaddour
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S. Haddad LPMC, Département de Physique, Faculté des
Sciences de Tunis, Tunisia
S. Charfi-KaddourLPMC, Faculté des Sciences de Tunis, Tunisia
M. HéritierLPS, Orsay, (unité mixte de Recherche) CNRS-Paris
XI, FranceR. Bennaceur
LPMC, Faculté des Sciences de Tunis, Tunisia
Interplay between SDW and superconductivity in the quasi-one organic
superconductor (TMTSF)2ClO4
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Acknowledgments
Theory ExperimentsC. Bourbonnais (Sherbrooke) D. Jérome (Orsay)A. G. Lebed (Arizona) Y. Maeno (Kyoto)
N. Joo (Orsay)
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Why quasi-one organic superconductors?
(TMTSF)2ClO4: an exotic organic conductor
Effect of disorder on the interplay between Superconductivity and SDW
Effect of a magnetic field: new field induced SDW (FISDW) phases
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Why superconductors ?
Uses for superconductors:
Also as … Electric generator (99% more efficient than ordinary one)SQUID (Superconducting Quantum Interference Device): sensing weak magnetic field Military: antenna and in detecting mines (US NAVY) …
IRM Accelerator LHC (CERN)
Maglev in Japan: fast, safe and economic
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The future of Superconductors
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Why organic superconductors ?
Dream: towards room temperature superconductors !!!
Problems: difficulties to synthesize such materials until…
Little’s Proposition (1964): look for organic conductors with one dimensional character to get high Tc !!!
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Why organic superconductors ?
But: there are still open questions !!!
1979: discovery of organic superconductivity in a quasi-one dimensional salt (TMTSF)2PF6 (D. Jérome’s group) …then in Bechgaard salts denoted by (TMTSF)2X (X=PF6
-, ClO4-
…)
Interplay between SC/ SDW: coexistence or competition?
SDW
SC
BUT : TC=1.2 K (so low !!!)
a complete laboratory for physicists intensive study
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Needle like
Crystal structure of (TMTSF)2X
TMTSFX
TMTSF=tétraméthyl-tétraséléna-fulvalèneX= anion: Br-, PF6
-; ClO4-…
c
ba
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ab
c
Organic chains of TMTSF molecules
Conducting planestbta
Key parameters of (TMTSF)2X
tc
t’b
tc « tb « ta c «b« a quasi-1D conductors
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0 10 20 30 40 50 60 70 80
1
10
100
1000
T*
T ()B
r
ClO
4
PF6X = B
F 4
PF6
Tem
pera
ture
(K)
(TMTTF)2 X
M-H
Pressure (kbar)
SC
METAL
AF SDWSP
(TMTSF)2 X
1D LL
2D FL
Phase diagram of Bechgaard salts
AF SC T. Vuletic, et al. Eur. Phys. J. B 25, 319 (2002)
(TMTSF)2ClO4 is superconducting at ambient pressure (Tc= 1.2 K)
ClO
4
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(TMTSF)2ClO4 : What makes it so special ?
TMTSFClO4
ab
c
ClO4 anions are noncentrosymmetric
2 possible orientations or
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(TMTSF)2ClO4 : anion ordering
Anion ordering in (TMTSF)2ClO4
ClO4 TMTSFb
c
t b
Slowly cooled sample (relaxed):
ClO4 anions order along b direction at TAO = 24 K
Rapidly cooled sample (quenched):
ClO4 anions disordered ! V = 0
Periodic potential:
V (y) =V cos( /b y)
V: anion potential
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2VFermi surface of (TMTSF)2ClO4
k ┴
k
Fermi surface of (TMTSF)2X without anion ordering
Dispersion relation of relaxed (TMTSF)2ClO4
bktVbktkkvk bbFF 2cos2 cos4 222
Two-band energy spectrum
BBA A
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Joo et al., Euro. Phys. Lett. 72, 645 (2005)
Effect of cooling rate
In the quenched samples:
pure magnetic state (SDW)
Puzzles !!!
SC
SDW
relaxed samples (slowly cooled) :
Superconducting (SC)
For the intermediate cooling rate:
both SC and magnetism.
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TSCSC/
SDW
TSDW
Cooling rate
T
effect of cooling rate: generic phase diagram
metal
Pure SC
Pure SDW
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Model :Interplay of superconductivity and magnetic
phases
Anion ordering two band energy spectrum
(k)
k
A B
kFA
kFBEg
Bands separated by gap Eg
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Method: perturbative renormalization group theory (Bourbonnais et al.)
Eg
tb
MV
system set of coupled chains
singlet superconductivity (SSc)
MV CDW SDW
triplet superconductivity(tSc)
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m
Scattering processes:(g-ology model)
g(1) processes g(2) processes
m m
m
m
m m
m m
m m
m
m m
m
(1)0g (1)
bg
(1)tg(1)
fg
m
m m
m
m
m m
m m
m
m
m
m
m
m
m
m
(2)0g (2)
bg
(2)fg(2)
tg
Most divergent the most dominant fluctuation.
MV
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Eg = 5 K
Rapid cooling
Eg = 8 K
Intermediate cooling
Eg = 15 K
Slow cooling
Scaling flows of the most divergent MV
tb = 300 K, EF = 2000 K, Tcross= 170 K, = 0.6 (i)g
Singlet SC Coexisting singlet SC/SDW
Pure SDW
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Phase diagram
pure singlet SC (SCs) phase(SCs + SDW) pure SDW
Limits RG calculations:
Is there coexistence or
segregation
between SC and SDW ?
Cooling rateS. Haddad et al. to appear in J. Low Temp. Phys.
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Experiments
Phase segregation !
Ordered ClO4 region
SC
SC
SCSDW
Disordered ClO4 region
decrease cooling rate(decrease disorder)
Next step: compare free energies (pure SC, pure SDW, SC+SDW)
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Effect of a transverse magnetic fieldH
a
b
c
Organic chains
Cascade of field-induced SDW (FISDW) phases
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Other puzzle: Effect of a high magnetic field
Generic Temperature field phase diagram in the absence of anion
ordering:
2
4
6
8
10
Tem
pera
ture
(K)
5 10 15 20 25
N=0
N=123
metal
Cascade of FISDW phases :already explained within the Quantized nesting model (Lebed, Gor’kov, Maki, Héritier, Montambaux, Lederer).
Magnetic field (T)
SDW phase inside an original SDW state !!!
Temperature field phase diagram in the (TMTSF)2ClO4 (Chung et al. 2000)
SDW I
SDW III
SDW IISDW IV
?
??
Ok-Hee Chung et al., PRB 61 (2000)
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2
4
6
8
10
Tem
pera
ture
(K)
5 10 15 20 25
N=0
N=123
metal
Magnetic field (T)
High field phases correspond lowest N values
Focus on N=0 and N=1 phases
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Gvt
VJF
b40 G=eHb/hc, b interchain distance
In the presence of magnetic field: effective anion gap
27Bq0
Aq0 q1
Intraband nesting: N=0 phase
Osada et al. (Phys. Rev. Lett. 1992)
Interband nesting: N=1 phase
(k)
k
A B
N=0Tow nesting vectors
k
A B
N=1one nesting vector
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Instability criteria
Tvg
gTQ
g F
mm
b ,4 21 ,
21 1
)2(
)2(
00
)2(00
N=0 FISDW phase: Generalized Stoner Criterion
Term describing the overlap of the tow SDW components appearing
on the two bands
Intraband term
N=1 FISDW phase: standard Stoner Criterion
, 1 21 1
11)2(
)2(
)2( TQgg
gff
t
MFT + RG
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Thermodynamics:Competition between the N=0 and the N=1 phase
F
T
F1
F0
T1 T0
T*1
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Temperature-field phase diagram
Experiments (Chung et al. 2000)
?
?
?
Our model
S. Haddad et al. Phys. Rev. Lett., 89, 087001 (2002)S. Haddad et al. Phys. Rev B, 72, 085104 (2005)
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Effect of a parallel magnetic field
H
a
b
c
Organic chainsa
Confinement inthe (a,b) plane
b
Free of bird flu !
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Experiment (Danner et al. 1997)
Our model
submitted to Eur. Phys. J. B
Joo et al. 2006
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Quantum mechanical calculation
Layer index
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Other models in competition with our !!!
Index layer
Probability in transverse direction
A. G. Lebed, Phys. Rev. Lett. (2005)
But, does not explain the resistance
behavior
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What should be next ?
symmetry of the gap in (TMTSF)2ClO4? triplet or singlet ?
Interplay between Superconductivity and SDW : coexistence or competition ?
SDW
Sc