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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, Bayerische Akademie der Wissenschaften, Garching, Germany Ilya Sheikin Laboratoire National des Champs Magnétiques Intenses, Grenoble, France Harald Müller 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 Nesting instability of the Fermi surface • CDW formation at8 K very low!! a-(BEDT-TTF)2KHg(SCN)4: basic features 2D Fermi surface [P. Foury-Leylekian et al., PRB 2010] smallDCDW kBTCDWhigh sensitivity to external conditions: pressure, magnetic field

  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 space orbit: 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. Zanchi et al., PRB 1996

  8. CDW in a magneticfield • Orbital effect (requires an imperfectly nested FS): stimulates CDW Angle-dependent MagnetoResistance Oscillations (AMRO) in a-(BEDT-TTF)2KHg(SCN)4 field-induced CDW state R^(W) q (deg) normal state normal state M.K. et al., SSC 1994 P > Pc ambient pressure

  9. 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. Zanchi et al., PRB 1996 L. Gor’kov & A. Lebed, J. Phys. Lett. (Paris) 1984

  10. 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]

  11. 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

  12. 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) – inhomogeneous superconductivity at P = 0

  13. Superconductivity vs. CDW • Onset of superconductivity

  14. 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!

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

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

  17. Superconductivity in a magneticfield; P > Pc T = 90 mK

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

  19. 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.

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