TRANSIENT DIFFERENTIAL REFLECTIVITY AND NONEQUILIBRIUM ELECTRON RELAXATION IN Y1-X-YPRXCAYBA2CU3O7 THIN-FILMS

We report systematic studies of the transient differential reflectivit y Delta R/R in YBa2Cu3Cu7-delta film's with different oxygen contents and in Y1-x-yPrxCayBa2Cu3O7 thin films with different compositions. Th e spectra have been used to analyze the nonequilibrium electron dynami cs and the related position of the Fermi level to the filled Cu d(9)/d (10) band. The Delta R/R changes sign in YBa2Cu3O7-delta system with d elta=0.1 and in Y1-xPrxBa2Cu3O7 system with x=0.5 for probe photon ene rgy of 1.92 eV. The transient differential reflectivity measurement se ems to reveal that the substitution of Pr for Y ions in Y1-xPTxBa2Cu3O 7 system and the oxygen deficiency in YBa2Cu3D7-delta system have simi lar effects on the related Fermi level position. The influence of part ial substitution of divalent Ca ions for Pr, however, cannot be simply understood from the hole filling model. These results and variation o f the relaxation time for nonequilibrium electrons suggest that other effects should be considered.