ANOMALIES IN THE TEMPERATURE BEHAVIOR OF ABSORPTION IN THE OPTICAL 1.5-3.0 EV RANGE FOR THE HIGH-T(C) SUPERCONDUCTOR YBA2CU3O7-DELTA

Spectral and temperature measurements of the absorption coefficient, k appa(E, T), have been performed within a dielectric transparency windo w (from 1.5 to 3 eV) which persists in the metal phase. An unusual tem perature-dependent increase in absorption was observed above T(c) for the metal phase. In combination with the measured absorption spectra a nd their concentration dependences it indicates an important role for the metal-type intraband transitions which is enhanced with oxygen con centration. It is concluded that there occurs a noticeable temperature -dependent redistribution of electrons between the CuO2 plane and the reservoir of charges. The kappa(T) curve has a peculiarity at T(c) and follows the superconducting pp width below T(c). All the peculiar fea tures of kappa(T) are conditioned by the narrowness of the conduction hole band and provide information on the electron structure near the F ermi level.