Fermi surface and resistance anomalies in ET-TCNQ

Recently, a new organic conductor ET-TCNQ, which exhibits two resistance anomalies at T 1 = 80 K and T 2 = 20 K, was synthesized. We present a systematic study of transport properties of ET-TCNQ under magnetic fields. Shubnikov-de Haas (SdH) oscillations are clearly observed and we find five distinct small Fermi surfaces (FS's). The cross-sectional areas of FS are estimated to be from I %(α) to 3.5 %(e) of the first Brillouin zone. We detect Lebed resonance and Danner-Chaikin oscillation in measurements of angular-dependent magnetoresistance oscillation (AMRO), suggesting the existence of the quasi-one dimensional FS related to ET molecules. The origins of the two resistance anomalies are discussed in terms of nesting-driven density-wave transition.