Fermi surface and low temperature structure in (DMET-TSeF)2Au(CN)2

The title compound is one of the DMET-TSeF salts which are quasi-one-dimensional organic metals at room temperatures. We show that the compound has a closed Fermi surface using the angle-dependent magnetoresistance oscillation (AMRO) method together with magnetoresistance and magnetization quantum oscillation measurements at low temperatures. By the X-ray measurement, we confirm that the structural phase transition observed around 180 K is related to the anomaly observed in the temperature dependence of the resistivity [1]. The nesting vector has the direction of 0.5a*+0.5c*. The obtained low temperature closed Fermi surface has about 4 % of the first Brillouin zone area. The AMRO data show the existence of a very anisotropic Fermi surface where the diameter perpendicular to the most conducting a direction is about 0.5 c*. The possible origin of the low temperature closed Fermi surface is discussed and the relation to the ordering of anion molecules is considered as the probable reason.