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Is the t -type Conductor, t -(EDO- S,S -DMEDT-TTF) 2 (AuCl 2 ) 1+ y , Clean or Dirty ?

Is the t -type Conductor, t -(EDO- S,S -DMEDT-TTF) 2 (AuCl 2 ) 1+ y , Clean or Dirty ?. T. Nakanishi, M. Teramura, L. Li, T. Fujimoto, S. Yasuzuka, Keizo Murata. Osaka City Univ., Japan. T. Sasaki. Tohoku Univ., Japan. T. Konoike, T. Terashima, S. Uji.

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Is the t -type Conductor, t -(EDO- S,S -DMEDT-TTF) 2 (AuCl 2 ) 1+ y , Clean or Dirty ?

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  1. Is the t-type Conductor, t-(EDO-S,S-DMEDT-TTF)2(AuCl2)1+y, Clean or Dirty ? T. Nakanishi, M. Teramura, L. Li, T. Fujimoto, S. Yasuzuka, Keizo Murata Osaka City Univ., Japan T. Sasaki Tohoku Univ., Japan T. Konoike, T. Terashima, S. Uji Nat’l Res.Inst.Mat., Japan Y. Nogami Okayama Univ., Japan G. C. Anyfantis, G. C. Papavassiliou Nat’l Hell’c Res. Found., Greece

  2. Previous works 1 ~ dirty or clean ? ~ T.Konoike et al., PRB66 (2002) 245308. Dirty ? Clean ? Res. Upturn, Small RRR, Sample Dependent, Negative MR with Large Hysteresis SdH (TD = 1.4 K !!) No Sample Dependence Quantum Hall Effect

  3. Scatter inr(T) is not related to SdH AuBr2 -salt Sample dependent r(T) Almost the same oscillations Band structures are the same. Observed at Tallahassee with Brooks

  4. Structure t-(EDO-S,S-DMEDTTTF)2(AuX2)1+y Cond. layer Ins. layer EDO-S,S-DMEDT AuX2 X = Cl, Br, I Space group I4122 c b a a G.C.Papavassiliou et al., Mol. Cryst. Liq. Cryst., 285 (1996) 83.

  5. disorder t-(EDO-S,S-DMEDT-TTF)2(AuX2)1+y Cond. layer • ethylinedioxy-group • anion defect (ins.layer) (diffuse streak) • anion mixing AuBr2 -salt (AuBr2) 1-x( AuCl2) x from solvent, DCE Ins. layer EDO-S,S-DMEDT OOSS-AuBr2 c a

  6. Previous works 2 ~ magnetic feature ~ AuBr2-salt T.Konoike et.at, Synth. Met., 120 (2001) 801. Saturation of M =>Ferro-like but no coercive force.

  7. Previous works 2 ~ magnetic feature ~ c B f b a // a // a+b // b H. Yoshino et.at, J. Phys. Soc. Jpn. 68 (1999) 177. AuBr2-salt Symmetry change 5 T => 0.5 T C4 => C2 Hysteresis (#2 & #3) Existence of domain ? (Ferro) 0 T 5 T 0.5 T

  8. This work Previous works but mixed with AuCl2 from solvent, DCE AuBr2-salt AuCl2-salt pure anion

  9. Experiment • Resistance • X-ray diffraction • Magnetoresistance • Magnetization Examined • Magnetic phase in low temperature • Magnetic field effect to M and r ( relation between M and r )

  10. r (T) （AuCl2)1+y r// r^ Steep rise at 20 K (No hysteresis)

  11. r (T, B) r^ (W) r// (W)

  12. X-ray diffraction ~ No new superstructure across 20 K ~ 9 K 24 K CuKa, 15 kV-30 mA, 10 h exposing

  13. Magnetoresistance c B I b a hysteresis Rapid decrease saturates 1~1.5 T.

  14. SdH Effect m/m0= 1.2 TD = 1.5 K very clean! AuCl2; Only one Fermi pocket (17 T 0.2 %) => metal ref: AuBr2; Two pockets (50 T 0.66 %, 481 T 6.1 %)

  15. Results (1) ~ transport ~ • Resistivity => dirty feature ? Steep rise anomaly at 20 K without hysteresis. not CDW (X-ray). • SdH oscillation => very clean !! One Small Fermi surface Pocket (metal). Very low Dingle temperature (TD = 1.5 K). • Magnetoresistance => related to magnetism. Large negative magnetoresistance (~ 80 % at 27 T). The decrease saturates at higher field (B < 2 T) Hysteresis (low T > high T). The anomaly vanishes by 5 T (TC increases). Contrast between FC & ZFC (Spin-Glass?).

  16. M – H Curve dM/dH saturates ~1 T like MR. r is related toM

  17. c–T Curve FC ZFC 1 T : Peak at 20 K irreversible (FC & ZFC) 5 T : nothing

  18. FC & ZFC, Remnant M T T IRM TRM 0 T B 0 T B Temperature (K) Thermal Remnant Mag’n polycrystal Isothermal Remnant Mag’n Remnant M exists and vanishes ~ TC = 20 K

  19. Possible state? AF cant-AF F SG Remnant M M - H curve × ○ △ ○ FC &ZFC × ○ ○ ○ Peak at 20 K ○ ○ × ○ TC vanishes under 5 T ？ ？ ？ ○ ‘Spin-Glass’ with ‘Canted AF’

  20. Results (2) ~ magnetism ~ • M - H Curve dM/dH saturates at low field. • M - T => related to r(T) Peak at 20 K (vanishes at 5 T). Different between FC & ZFC. • Remnant Magnetization exists TRM large. IRM small or nothing. • Spin-Glass based on canting-AF

  21. Magnetic field effects on M and r Low field high field uniform Spin direction random disorder order M neg. mag saturates & SdH Mag. Resistance

  22. Conclusion • History (Field and Temp.) strongly influences to reversible and irreversible properties very clearly in both r and M. First Example in Organic Conductors • The possible ground state is Spin-Glass with Canting-AF. • The system changes from‘dirty’ to ‘clean’ by increasing magnetic field.

  23. Thank you. Dep’t. of Mat. Sci., Grad. School of Sci., Osaka City Univ., Osaka 558-8585, Japan muratak@sci.osaka-cu.ac.jp nakanisi@sci.osaka-cu.ac.jp

  24. r (B) Dr/rB=0 Magnetic Field (T) hysteresis Rapid decrease saturates 1~1.5 T.

  25. Quantum Hall Effect in a new Mechanism Intermed. temp.（4He temp.） Empty Empty Fermi Surface of 6 % plays a role of elec. reservoir εF Partially filled completely filled filled 6 % 0.6 % <= Fermi Surface/BZ 3.5～5.2 1.3<=m*/me courtesy of Y. Hasegawa

  26. Rxy at intermed. temp.

  27. Pressure effect

  28. Structure ~ dispersion relation ~ Conduction layer large pocket (star shape) small packet Ins. layer ~ disorder ~ OOSS-AuBr2 • ethylinedioxy-group • anion mixing (AuBr2 => AuCl2) • anion defect (ins.layer) (diffuse streak) c a

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