PULSED TERAHERTZ-BEAM SPECTROSCOPY AS A PROBE OF THE THERMAL AND QUANTUM RESPONSE OF YBA2CU3O7-DELTA SUPERFLUID

Pulsed terahertz spectroscopy is used to determine the superfluid resp onse of a YBa2Cu3O7-delta film under both thermal and optical stimulat ion. The coherent, time-domain technique is used in a novel configurat ion to directly measure the complex conductivity of the film versus te mperature and continuous-wave laser illumination. At 0.6 T-c, the supe rfluid shows an identical response regardless of whether the stimulus is thermal or optical. This contrasts with the behavior of the superfl uid at 0.26 T-c, where dramatic differences are observed depending on whether the sample is heated or subjected to optical illumination. It is suggested that these differences arise from an enhanced contributio n due to quantum effects, and thus also from a strong temperature depe ndence of the quasiparticle recombination time at low temperatures. (C ) 1995 American Institute of Physics.