Shubnikov-de Haas oscillations in the two-dimensional organic conductor τ-(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y (y∼0.75) -: art. no. 245308

The quasi-two-dimensional organic tau-type conductor, tau-(EDO-S,S-DMEDT-TTF)(2)(AuBr2)(1+y) (ysimilar to0.75), shows metallic temperature dependence of the resistivity down to T(min)similar to50 K, below which resistance upturn is observed. There has been no evidence of the phase transition through T-min. In this work, in pursuit of direct evidence for metal at low temperature by transport measurement, we show an observation of the Shubnikov-de Haas (SdH) oscillations for this salt. The observed frequencies of the oscillations are inconsistent with the previous band calculation. Further, it is remarkable that the amplitude of the oscillation was so giant (\Deltarho/rho(0)\similar to30%), and the oscillation above 20 T corresponds to a N=2 Landau state, i.e., next to a quantum limit. We also observed the SdH oscillations in other tau-type conductor, tau-(P-S,S-DMEDT-TTF)(2)(AuBr2)(1+y) (ysimilar to0.75), which almost reproduced the previous report by Storr.