Temperature Dependence of Reflectance Spectrum of (SN)_xSingle Crystal

The plasma edge around 2.7 eV in the reflectance spectrum of (SN) x single crystal for E // b -axis polarization shows the blue shift with lowering temperature. The relaxation time of the free electron estimated from the reflectance spectrum at 4.2 K is slightly larger than that of 300 K by the factor of 1.5, resulting in the much smaller temperature dependence of the σ opt (conductivity at optical frequency) compared with that of σ dc (conductivity at dc). Several models which explain these results are discussed.