OPTICAL-RESPONSE TO SUPERCONDUCTING TRANS ITION IN INFRARED REFLECTION AND TRANSMISSION OF YBACUO

Reflection and transmission spectra of YBaCuO thin films with a modera te oxygen content are measured in the near infrared range of 2 500 to 10 000 cm(-1) with varying temperature from 300 to 10 K. It is found t hat the optical response to superconducting transition depends oct the state of temperature equilibrium and the conditions of sample thermoc ycling. The reflection and transmission spectra are different sensitiv ity to the YBaCuO structures below and above the critical temperature T, which separates the states with various degree of localization of the carries. It is shown that there are two contributions to the IR sp ectral functions from different groups of the carriers, which generate the superconducting condensate.