Fermi surface and pressure effect in (BEDT-TTF) 2Cu(NCS) 2

Abstract

We have recently reported on the Shubnikov-de Haas (SdH) effect and the Fermi surface in the title compound. The SdH signal observed corresponds to the cylindrical closed Fermi surface with the area of the extremal orbit, 18 % of the first Brillouin zone. The corresponding Fermi surface can be obtained using the tight-binding band calculation based on the extended Hückel approximation. In this case the validity of the simple theory is confirmed. We report on the pressure effect in the SdH effect. The SdH period decreases as the pressure increases. The preliminary result indicates the decrease in the effective mass. The decrease of the oscillation period gives the same order of compressibility of the crystal as the ß-(BEDT-TTF) 2I 3 salt. The decrease in the effective mass cannot be understood by the simple band theory. The decrease may correspond to the decrease in the electron-photon interaction resulting in the lower superconducting transition temperature.