Reflection spectroscopy of τ-type organic conductors under the magnetic field

A T-type organic conductor, τ-(P-S,S-DMEDT-TTF)2(AuBr 2 ) 1+y , (y∼0.75) shows large negative magnetoresistance (ΔR/R ∼ -0.9) and Shubnikov-de Haas (SdH) oscillations originated from small Fermi pockets at low temperature in the apparent semiconducting state. Polarized reflectance spectra were measured to elucidate the effect of the magnetic filed on the low temperature electronic state. Temperature dependence of the spectra shows at least four kinds of temperature regions divided at 11, 40 and 100 K, respectively. It was succeeded to observe the relatively large recovery of spectral intensity especially below 1500 cm -1 by the application of the magnetic field along the c-axis (Faraday configuration), while the magnetic field gives minor effect on the spectral shape in the energy range in this study.