TEMPERATURE SINGULARITIES IN REFLECTION SPECTRA OF YBACUO SUPERCONDUCTING FILMS IN THE INFRARED FREQUENCY-RANGE

The reflection spectra of YBaCuO superconducting films with moderate a nd optimal doping are measured in the IR region (2500-10000 cm(-1)) by varying temperature in the interval 5-200 K. The experimental results convincingly confirm an optical response to the superconducting trans ition occurring at the point T = T-c and the sensitivity of optical IR spectra to the phase ordering temperature T = T > T-c. It is found t hat samples with optimal doping display reproducible temperature chang es at T > T-c. It is shown that the two-component model of carriers, including light fermions and heavy bosons, is most adequate for a desc ription of the entire body of optical data. Optical data are used for reconstructing the phase diagram for YBa2Cu3O6+x in the T vs. x coordi nates. (C) 1998 American Institute of Physics. [S1063-777X(98)00103-0] .