EVIDENCE FOR 2-COMPONENT HIGH-TEMPERATURE SUPERCONDUCTIVITY IN THE FEMTOSECOND OPTICAL-RESPONSE OF YBA2CU3O7-DELTA

Femtosecond time-resolved spectrocopy has been used to investigate ele ctronic excitations contributing to the superconducting gap function D elta(omega,T) in YBa2Cu3O7-delta. The optical response is strongly pea ked at 1.5 eV, and contains two distinct components: one with a charac teristic relaxation time of similar to 5 ps, whose amplitude displays a two-fluid-like temperature dependence, and a long-lived component (> 10 ns) which is consistent with localized quasiparticle states at the Fermi energy. The latter shows activated behavior below T-c with an ac tivation energy 2 Delta(0) approximate to 3.5kT(c).