S. Haddad

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Interplay between SDW and superconductivity in
the quasi-one organic superconductor (TMTSF)2ClO4

• S. Haddad
• LPMC, Département de Physique, Faculté des
  Sciences de Tunis, Tunisia
• S. Charfi-Kaddour
• LPMC, Faculté des Sciences de Tunis, Tunisia
• M. Héritier
• LPS, Orsay, (unité mixte de Recherche) CNRS-Paris
  XI, France
• R. Bennaceur
• LPMC, Faculté des Sciences de Tunis, Tunisia

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• Acknowledgments
• Theory Experiments
• C. 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)

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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
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Why organic superconductors ?

• 1979 discovery of organic superconductivity in a
  quasi-one dimensional salt (TMTSF)2PF6 (D.
  Jéromes group)
• then in Bechgaard salts denoted by (TMTSF)2X
  (XPF6-, ClO4-)

But there are still open questions !!!
Interplay between SC/ SDW coexistence or
competition?
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Crystal structure of (TMTSF)2X
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Key parameters of (TMTSF)2X
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Phase diagram of Bechgaard salts
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(TMTSF)2ClO4 What makes it so special ?
ClO4 anions are noncentrosymmetric
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(TMTSF)2ClO4 anion ordering
Slowly cooled sample (relaxed) ClO4 anions
order along b direction at TAO 24 K
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Effect of cooling rate
relaxed samples (slowly cooled)
Superconducting (SC)
For the intermediate cooling rate both SC and
magnetism.
In the quenched samples pure magnetic state
(SDW)
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effect of cooling rate generic phase diagram
T
metal
TSDW
Pure SDW
TSC
SC/ SDW
Pure SC
Cooling rate
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Model Interplay of superconductivity and
magnetic phases
Bands separated by gap Eg
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Method perturbative renormalization group theory
(Bourbonnais et al.)
SDW
CDW
singlet superconductivity (SSc)
triplet superconductivity(tSc)
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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
m
m
m
m
m
m
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Scaling flows of the most divergent
tb 300 K, EF 2000 K, Tcross 170 K,
0.6
Coexisting singlet SC/SDW
Singlet SC
Pure SDW
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Phase diagram
Limits RG calculations Is there coexistence
or segregation between SC and SDW ?
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Experiments
Phase segregation !
Next step compare free energies (pure SC, pure
SDW, SCSDW)
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Effect of a transverse magnetic field
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Other puzzle Effect of a high magnetic field
Generic Temperature field phase diagram in the
absence of anion ordering
10
8
metal
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Temperature (K)
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N0
2
N1
2
3
5
10
15
20
25
Magnetic field (T)
Cascade of FISDW phases already explained
within the Quantized nesting model (Lebed,
Gorkov, Maki, Héritier, Montambaux, Lederer).
SDW phase inside an original SDW state !!!
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High field phases correspond lowest N values
10
8
metal
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Temperature (K)
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N0
2
N1
2
3
5
10
15
20
25
Magnetic field (T)
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Instability criteria
MFT RG
N1 FISDW phase standard Stoner Criterion
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ThermodynamicsCompetition between the N0 and
the N1 phase
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Temperature-field phase diagram
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Effect of a parallel magnetic field
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Quantum mechanical calculation
Layer index
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Other models in competition with our !!!
Probability in transverse direction
A. G. Lebed, Phys. Rev. Lett. (2005)
Index layer
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 ?

• 
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