Thermal expansion of organic superconductor α-(BEDT-TTF)2 NH4Hg(SCN)4
A.V. Dolbin, M.V. Khlistuck, V.B. Eselson, V.G. Gavrilko, N.A. Vinnikov, R.M. Basnukaeva, and V.A. Konstantinov
B. Verkin Institute for Low Temperature Physics and Engineering, NAS of Ukraine 47 Nauky Ave., Kharkov 61103, Ukraine
V.N. Karazin Kharkiv National University, 4 Svobody Sq., Kharkov 61022, Ukraine
Department of Chemistry, Graduate School of Science, Osaka University 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
Received July 17, 2018, published online November 26, 2018
The temperature dependence of the linear thermal expansion coefficients (LTEC) of a single crystal of α-(BEDT-TTF)2NH4Hg(SCN)4 where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene was studied by the method of precision capacitive dilatometry in the temperature range 2–250 K along the crystallographic direction b (perpendicular to the crystal layers). Negative values of LTEC were found below 4 K. Probably it is due to charge fluctuations as the temperature approaches the temperature of transition to the superconducting state Tc. It has been suggested that the bends on temperature dependence of LTEC observed in the temperature range 25–45 K are related to order-disorder arrangement of NH4+ ions. Weak maximum of the LTEC, detected at a temperature of about200–220 K, can be caused by the processes of charge redistribution and the associated intermolecular interaction fluctuations.
Key words: organic (super) conductors, α-(BEDT-TTF)2NH4Hg(SCN)4, thermal expansion.