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Magnetic field effects on the CDW and SC states in  -(BEDT-TTF) 2 KHg(SCN) 4

Magnetic field effects on the CDW and SC states in  -(BEDT-TTF) 2 KHg(SCN) 4. Dieter Andres, Sebastian Jakob , Werner Biberacher , Karl Neumaier and Mark Kartsovnik Walther-Mei ß ner-Institut , Bayerische Akademie der Wissenschaften , Garching , Germany Ilya Sheikin

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Magnetic field effects on the CDW and SC states in  -(BEDT-TTF) 2 KHg(SCN) 4

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  1. Magnetic field effects on the CDW and SC states in -(BEDT-TTF)2KHg(SCN)4 Dieter Andres, Sebastian Jakob, Werner Biberacher, Karl Neumaier and Mark Kartsovnik Walther-Meißner-Institut, BayerischeAkademiederWissenschaften, Garching, Germany Ilya Sheikin Laboratoire National des Champs MagnétiquesIntenses, Grenoble, France HaraldMüller European Synchrotron Radiation Facility, Grenoble, France Natalia Kushch Institute of Problems of Chemical Physics, Chernogolovka, Russia

  2. a-(BEDT-TTF)2KHg(SCN)4: basic features BEDT-TTF molecule: bis(ethylenedithio)-tetrathiafulvalene b c a a T. Mori et al., Bull. Chem. Soc. Jpn. 1990; R. Rousseau et al., J. Phys. I (France) 1996; P. Foury-Leylekian et al., PRB 2010 r||(300K) 10 - 20 mW•cmr/r|| ~ 104- 105ra/rc 2 r (300K) / r (1.4K) ~ 102t ||/t  670  ,coh/||  2.210-6

  3. Q Nestinginstability of the Fermi surface • CDW formation at8 K verylow!! a-(BEDT-TTF)2KHg(SCN)4: basic features 2D Fermi surface [P. Foury-Leylekian et al., PRB 2010] smallDCDW kBTCDWhighsensitivitytoexternalconditions: pressure, magneticfield

  4. CDW in a magneticfield • Pauli paramagnetic effect: suppresses CDW [W. Dieterich & P. Fulde, 1973] Phase diagram of a-(BEDT-TTF)2KHg(SCN)4 P. Christ, W. Biberacher, M.K., et al., JETP Lett. 2000 Q- TCDW/TCDW(0), exp 2mBB/hvF B NM CDWx ~ 23 T CDW0 Q+ Q-< Q+ TCDW/TCDW(0) Theory: A. Buzdin & V. Tugushev, JETP 1983 D. Zanchi et al., PRB 1996; P. Grigoriev & D. Lyubshin, PRB 2005

  5. CDW in a magneticfield • Orbital effect (requires an imperfectly nested FS): stimulates CDW

  6. Real spaceorbit: Dy ~ 1/Bz electrons become effectively more 1D CDW in a magneticfield • Orbital effect (requires an imperfectly nested FS): stimulates CDW

  7. a-(BEDT-TTF)2KHg(SCN)4 D. Andres, M.K., et al., PRB 2001 CDW in a magneticfield • Orbital effect (requires an imperfectly nested FS): stimulates CDW Theory: D. Zanchiet al., PRB 1996

  8. a-(BEDT-TTF)2KHg(SCN)4 D. Andres, M.K., et al., PRB 2001 FICDW at t^’ > t^’ * ??? CDW in a magneticfield • Orbital effect (requires an imperfectly nested FS): stimulates CDW Theory: D. Zanchiet al., PRB 1996 L. Gor’kov& A. Lebed, J. Phys. Lett. (Paris) 1984

  9. CDW in a magneticfield • Field-induced CDW (FICDW) transitions The “slow oscillations” SdHo • appear at P  Pc  2.5 kbar • approximately periodic • with 1/B P = 3 kbar • display a weak hysteresis Positions of the FICDW transitions can be fitted with t^  0.5 meV [A. Lebed, PRL 2010]

  10. CDW in a magneticfield • Field-induced CDW (FICDW) transitions FISDW in (TMTSF)2PF6 FICDW in a-(BEDT-TTF)2KHg(SCN)4 A. Kornilov et al., PRB 2002 FICDW is weaker than FISDW due to the paramagnetic effect! A. Lebed, JETP Lett. 2003

  11. Superconductivity vs. CDW R  0 R = 0 Sample #2: zero resistance but no Meissner! R^ (Ohm) • Resistance at zero field See also: H. Ito et al., SSC 85 1005 (1993) – inhomogeneoussuperconductivityatP = 0

  12. Superconductivity vs. CDW • Onset of superconductivity

  13. Superconductivity vs. CDW • Onset of superconductivity CDW+SC R  0 R = 0 The SC onset temperature is 3 times higher in the SC/CDW coexistence region!

  14. Superconductivity in a magneticfield; P > Pc • Critical field ^ layers at P = 3 kbar:x||(0)  250nm cf. meanfreepath  1m

  15. Superconductivity in a magneticfield; P > Pc • Critical field // layers 1.6Hp0 Hp0: Chandrasekhar-Clogston paramagneticlimit GL: Hc2 (Tc-T ) dHc2/dT 12 T/K  x^(0) = 1.0 nmd/2; x||(0)/ x^(0)  250!

  16. Superconductivity in a magneticfield; P > Pc Directmanifestationoftheparamagnetic pair-breaking!

  17. Summary • CDW state: • richphasediagram due totheinterplayof • competingPauli paramagneticandorbital • effectsofmagneticfield • SC state: • at P < Pc: coexistswiththe CDW state; the • SC onsettemperatureisdrasticallyincreased • in thecoexistenceregion; • at P >Pc:bulk SC statewith a highly • anisotropic Hc2nearTc(0) and a clear • manifestationofparamagnetic pair-breaking • at H // layers.

  18. Qx = 2kF + NG, G = eayBz/ CDW in a magneticfield • Field-induced density wave transitions, t^’>t^’*: -kF kF B

  19. CDW in a magneticfield • Field-induced CDW (FICDW) transitions Commensurate splitting (A. Bjelis et al., 1999; A. Lebed, 2003) N = 3,4 2,3 “Spin-zero” 1,2 0,1 0 2QP = MG 2QP = (M + 1/2)G with M - integer

  20. CDW in a magneticfield • Field-induced CDW (FICDW) transitions 4 4 3 3 2 N = N = 5 3 2 2 1 1 1 0 0 0 Pauli effect on (FICDW) no Pauli effect (FISDW) Qx = 2kFQP + NG Qx = 2kF + NG G = 2eayBz/ QP = 2mBB/vF

  21. CDW in a magneticfield • Field-induced CDW (FICDW) transitions 4 3 3 2 N = 2 A. Lebed, JETP Lett. 78, 138 (2003) 1 1 0 0 Pauli effect on (FICDW) no Pauli effect (FISDW) Qx = 2kFQP + NG Qx = 2kF + NG G = 2eayBz/ QP = 2mBB/vF

  22. CDW in a magneticfield • Field-induced CDW (FICDW) transitions Spin-zero condition:  vF 1.2105 m/s

  23. Superconductivity vs. CDW • Onset of superconductivity Low Tc  weakfluctuations! CDW+SC Ginzburg-Levanyuk parameter: Gi(2)~ 10-5 R  0 R = 0 The SC onset temperature is 3 times higher in the SC/CDW coexistence region!

  24. Superconductivity in a magneticfield; P > Pc B (mT) • Critical field ^ layers

  25. Superconductivity in a magneticfield; P > Pc • Critical field // layers

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