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Magnetic field induced charge-density-wave transitions: the role of orbital and Pauli effects

Magnetic field induced charge-density-wave transitions: the role of orbital and Pauli effects. Mark Kartsovnik. Walther-Mei ß ner-Institut, BADW, Garching, Germany. Outline. Q. 2D Fermi surface. very low!!. a -(BEDT-TTF) 2 KHg(SCN) 4 : basic features. r || (300 K)  30 – 100 W cm;

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Magnetic field induced charge-density-wave transitions: the role of orbital and Pauli effects

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  1. Magnetic field induced charge-density-wave transitions: the role of orbital and Pauli effects Mark Kartsovnik Walther-Meißner-Institut, BADW, Garching, Germany

  2. Outline

  3. Q 2D Fermi surface very low!! a-(BEDT-TTF)2KHg(SCN)4: basic features r||(300 K)  30 – 100 Wcm; r^/r|| ~ 104- 105; r||(300 K)/r||(1.4 K)  102 T. Mori et al., 1990 Nesting instability of the Fermi surface • CDW formation at 8 K

  4. Pauli effect (isotropic) Spin splitting deteriorates the nesting conditions for a CDW Phase diagram of a-(BEDT-TTF)2KHg(SCN)4 P. Christ et al., JETP Lett. 2000 Q- TCDW/TCDW(0), exp B ~ 23 T suppresses CDW Q+ Q- < Q+ TCDW/TCDW(0) Theory: D. Zanchi et al., PRB 1996; P. Grigoriev&D.Lyubshin , PRB 2005

  5. Real space orbit: Dy ~ 1/Bz electrons become effectively more 1D Orbital effect (B || z)

  6. Orbital effect (B || z) a-(BEDT-TTF)2KHg(SCN)4 D. Andres et al., PRB 2001 Theory D. Zanchi et al., PRB 1996 FICDW at t^’ > t^’ * due to Landau quantization of the unnested FS pocket

  7. SdHo FICDW: experiment; B || z The “slow oscillations” • approximately periodic with 1/B • appear at P  Pc  2.5 kbar P = 3 kbar • display a weak hysteresis

  8. FICDW: experiment; B || z The “slow oscillations” • approximately periodic with 1/B • appear at P  Pc  2.5 kbar • display weak hysteresis • slightly shift with temperature  behaviour consistent with the FICDW scenario!!

  9. FICDW: experiment; B || z

  10. FICDW: experiment; B || z FICDW in a-(BEDT-TTF)2KHg(SCN)4 FISDW in (TMTSF)2PF6 A. Kornilov et al., PRB 2002 FICDW is weaker than FISDW due to the Pauli effect! A. Lebed, JETP Lett. 2003

  11. FICDW: role of the Pauli effect 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/h QP = 2mBB/hvF

  12. FICDW: role of the Pauli effect 4 3 3 2 N = 2 A. Lebed, JETP Lett. 2003 1 1 0 0 Pauli effect on (FICDW) no Pauli effect (FISDW) Qx = 2kFQP + NG Qx = 2kF + NG G = 2eayBz/h QP = 2mBB/hvF

  13. FICDW in a tilted field Commensurate splitting (A. Bjelis et al., 1999; A. Lebed, 2003) “Spin-zero” N = 3,4 2,3 1,2 0,1 0 2QP = MG 2QP = (M + 1/2)G with M - integer A. Lebed, JETP Lett. 2003

  14. FICDW in a tilted field: experiment T = 0.4 K Spin-zero condition:

  15. FICDW in a tilted field: experiment 1st CS angle Spin-zero condition:

  16. FICDW in a tilted field: experiment 1st CS angle Spin-zero condition:  vF 1.2105 m/s

  17. Summary • The orbital effect causes FICDW transitions in a-(BEDT-TTF)2KHg(SCN)4 at pressures above Pc = 2.5 kbar • The Pauli effect, in general, weakens the FICDW instability • The interplay between the orbital and Pauli effects can be controlled by changing the field orientation: - the FICDW is enhanced at commensurate splitting angles - the FICDW is suppressed at „spin-zero“ angles

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