TEMPERATURE-DEPENDENCE OF THE FAR-INFRARED MAGNETOTRANSMISSION OF YBA2CU3O7-DELTA FILMS

Measurements in circularly polarized light from 5 to 28 cm(-1) in magn etic fields up to 9T are reported. The zero field response is independ ent of temperature for T less than or equal to 30 K for clean samples and linear in T for films irradiated with alpha particles. Ln field th e transmission of the left circular polarization varies linearly with temperature up to 30 K and the right circular response is independent of temperature. The difference is maximum at lowest temperatures corre sponding to an electron active response and reverses sign at 20 K, The se results are interpreted in terms of the effects of thermally excite d quasiparticles in the mixed state.