INFRARED CONDUCTIVITY OF YBCO FROM TRANSMISSION AND REFLECTION SPECTRA OF THIN-FILMS

We measured far infrared transmittance and reflectance spectra of thin YBa2Cu3O7-x films grown on MgO. At 295 K reflectance measurements were extended up to 20 000 cm-1. We model the dielectric function of Y1Ba2Cu3O7-x by using free-carrier and mid-infrared terms. Our data are consistent with a huge mid-infrared component, in which low frequency contributions are very important and appear to be temperature dependent. The free-carrier term is described by the usual Drude model in the normal phase and by a two-fluid model in the superconducting phase.