Depinning of the Spin-density Wave in (TMTTF) 2 Br under Pressure

1. ECRYS-2005, Cargese Depinning of the Spin-density Wave in (TMTTF)2Br under Pressure K. Nomura Division of Physics, Hokkaido University, Japan

2. Collaborators K. Ishimura Hokkaido University K. Fujimoto Hokkaido University N. Matsunaga Hokkaido University T. Nakamura Institute for Molecular Science T. Takahasi Gakushuin University G. Saito Kyoto University

3. Outline 1. Introduction (Phase diagram of (TMTCF)2X under pressure) 2. Results of non-linear conductivity measurements Threshold electric field ET Hysteretic behavior in the I-V curve Excess conductivity carried by the SDW sliding 3. Summary

4. Crystal structure of (TMTCF)2X a transfer energy ta: tb : tc =250:10:1 (TMTTF) ta: tb : tc =250:25:1 (TMTSF) b Quasi-one dimensional conductor c

5. Generic phase diagram of (TMTCF)2X Jerome et al.

6. Sub-phase transition (with magnetic fluctuation) T*0.3TSDW

7. Generic phase diagram of (TMTCF)2X Jerome et al.

8. Increase of P Increase of 2D Decrease of I Decrease of TSDW0 Decrease of TSDW TSDW0: perfect nesting TSDW I : electron correlation TSDW(0) vs.coefficient C 6

9. The SDW transition Temperature dependence of resistance SDW transition temperature vs. pressure

10. Non-linear conductivity with the clearly defined threshold field ET Behaviors are qualitatively similar in each pressure Non-linear conductivity 0.5 Electric field dependence of conductivity

11. Larger value of ET for lower pressure Peak around T*0.3TSDW Temperature dependence of ET Temperature dependence of ET

12. Non-linear conductivity in (TMTSF)2ClO4

13. Larger value of ET for lower pressure Peak around T*0.3TSDW → magnetic fluctuation? Temperature dependence of ET Temperature dependence of ET Brown et al.

14. With decreasing temperature ET decreases well above T* → Impurity pinning as (TMTSF)2X salts Sharp drop below T* → Change of the pinning mechanism ET at high pressure region Temperature dependence of ET

15. Sample dependence of ET • Negligibly small peak in sample #2 • Steep decrease of ET below T* is common →Change of the pinning mechanism across T* Temperature dependence of ET

16. Hysteresis for the electric current sweep around ET Switching at Etup for the upward sweep Hysteretic behavior in the I-V curve I-V curve

17. Hysteresis is the largest at T* Hysteresis disappears at high and low temperature region → pinning mechanism changes at around T* Temperature dependence of hysteresis Temperature dependence of ETup and ETdn

18. Almost independent of pressure (although ET is strongly dependent on pressure ) → Sliding resistivity is not connected with pinning potential Dip at T* Sharp increase below T* Differential excess conductivity  Sliding resistivity The sliding is resistive around T* and becomes less resistive below T* Temperature dependence of exc

19. Sample dependence of differential excess conductivity Steep increase of excbelow T* The sliding becomes less resistive below T* Temperature dependence of exc

20. X-ray diffraction measurement in (TMTSF)2PF6  coexistence of the CDW above T* Coexistence of the SDW and the CDW Image for the coexistence Similar coexistence is expected in (TMTTF)2Br, in which the one-dimensionality in electron band is stronger. The CDW is expected to be strongly pinned than the SDW. decrease of ET and increase of excess conductivity below T*

21. Summary • Non-linear conductivity with the threshold electric field ET the sliding motion of the SDW • Temperature dependence of ET shows a steep drop below T* • Excess conductivity shows a sharp increase below T* • Sharp peak in ET and large hysteresis around T* for #1 • The coexistence of the CDW component is probably responsible for these phenomena

22. Thank You

23. Threshold field ET Excess conductivity Differential excess conductivity Definition of parameters 各パラメタｰの決め方

24. Non-linear conductivity in (TMTSF)2ClO4

25. Non-linear conductivity in (TMTSF)2ClO4