TEMPERATURE-DEPENDENCE OF THE MILLIMETER-WAVE CONDUCTIVITY OF YBA2CU3O7 AND BI2SR2CA1CU(2)O(8) THIN-FILMS AT 300-GHZ

A millimeterwave spectrometer using continuously tunable backward wave oscillators as sources and a quasioptical interferometer in the Mach-Zehnder configuration was used to measure the transmittivity in amplitude and phase of 60nm thin YBa2Cu3O7 and 250nm thin Bi2Sr2Ca1Cu2O8 films on NdGaO3 substrates at 300GHz for temperatures between 4K and 300K. From the spectra we derived the real and imaginary part of the dynamic conductivity sigma=sigma(1)i sigma(2) in the normal and superconducting state. From sigma(2) we got absolute values for the London penetration depth X. Beside the lower sigma(1)(T) values for the BSCCO films over the entire temperature range a clear maximum in sigma(1)(T) was measured at 60K for both compounds. The lambda(T) values of the BSCCO films are more than a factor of two higher in comparision to YBCO. Using a Drude-model for the normal and superconducting state a strong temperature decrease of the quasiparticle scattering rate tau(1)(T) below T-c was observed for both compounds, whereas the absolute tau(-1)(T) values are smaller for the BSCCO-films.