Magnetocapacitive effect in SDW system (TMTSF) 2 AsF 6

1. Magnetocapacitive effect in SDW system (TMTSF)2AsF6 D. Starešinić, D. Dominko, K. Biljaković Institute of Physics, Zagreb, Croatia P. Lunkenheimer, A. Loidl Institute of Physics, University of Augsburg, Germany

2. Phase diagram • new properties of SDW glass SDW1

3. Low temperature SDW phase dielectric response Lasjaunias et al. PRL 1994 thermodynamics NMR Takahashi et al. JPSJ 1986 also AMR, microwave response…

4. Multiferroic SDW relaxor ferroelectric SDW • SDW: incommensurate AFM + relaxor ferroelectric • two coexistent ferroic orders • possible multiferroic behaviour Nad et al. SSC 1995 Levstik et al. PRB 1998 Betouras et al. PRL 2007

5. Experiments • (TMTSF)2AsF6 • very similar to (TMTSF)2PF6 • Dielectric measurements in magnetic field • T down to 1.9 K • B up to 8 T • f 20 Hz – 1 MHz • j||a, B||c* • Vac=5 mV (instrument limit) • too low for high precision • too high for SDW systems (ET~10 mV/cm) Hemberger et al. Nature 2005

6. Resistance DLT B=8 T DHT B=0 T

7. Magnetoresistance • MR roughly linear in B • T dependence similar to (TMTSF)2PF6 1.9 K

8. Dielectric constant B=8 T B=0 T 80 Hz • Similar as in (TMTSF)2PF6 • B increases dielectric constant and relaxation time 1.6 kHz 300 kHz 300 kHz

9. Frequency dependence at 1.9 K 8 T Cole-Cole fit 0 T 8 T 5 T 0 T B||b’ 0 T

10. Parameters at 1.9 K • Littlewood’s pinning&screening theory does not work • De increases faster than the order parameter • B increases domain cooperativity?

11. Temperature vs field dependence 1.9 K 1.9 K 8 T 8 T Suggests B-T scaling! 0 T 2.9 K 8 T 1.9 K 0 T 2.9 K

12. Temperature dependence 8 T 0 T 8 T 0 T

13. Eact=26 K Eact=13 K Field dependence 1.9 K 2.6 K 1.9 K 2.6 K

14. Conclusions • huge magnetocapacitive effect in (TMTSF)2AsF6 • multiferroic nature of low temperature SDW state • not the consequence of screening • no simple relation between the De(B¸,T), t(B,T) and r(B,T) • further measurements with better samples at lower T, lower f and lower Vac