FEMTOSECOND RELAXATION DYNAMICS OF ELECTRONIC PROCESSES AND ELECTRON-PHONON COUPLING IN YBA2CU3O7-DELTA AND PRBA2CU3O7 EPITAXIAL-FILMS

The room temperature femtosecond relaxation dynamics of reflection spe ctra of YBa2Cu3O7-delta with different oxygen contents and PrBa2Cu3O7 epitaxial films have been studied. The relaxation times of Delta R(t) in YBa2Cu3O7-delta increase from less than 100 fs to more than 1 ps wi th increasing delta and with substitution of Pr for Y. The electron an d lattice temperature profiles at these quasi-equilibrium state are ca lculated from the nonequilibrium energy-balance model. The process of electron-phonon energy transfer was found to be dominated in our exper iments. These results reveal that in 123 phase superconductors decreas e of carrier concentration slows down the carrier-phonon coupling and the type of the electron-phonon interaction would be localized. The de pedence of electron-phonon coupling to oxygen defects in YBa2Cu3O7-del ta was found to be lambda similar to exp(-delta).