Giant Shubnikov–de Haas oscillation in τ-conductors

The magnetoresistance (MR) of two-dimensional organic τ-conductors, τ-(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y and τ-(P-S,S-DMEDT-TTF)2(AuBr2)1+y (y∼0.75) in high magnetic field was investigated. In both salts, large negative MR and Shubnikov–de Haas (SdH) oscillation were observed though the resistance of these compounds show upturn at low temperature. Especially for latter salt, the amplitude of SdH oscillation is so giant (|Δρ/ρ0|∼30%). From the frequency of the SdH, the area of Fermi surface for each compound is calculated to be 0.65, 6.1 and 6.8%, respectively. These values are not consistent with the previously calculated value of 12.5% for single star-shaped Fermi surface for y∼0.75.