Evidence for two-component high-temperature superconductivity in the femtosecond optical response of YBa2Cu3O7-delta

Femtosecond time-resolved spectrocopy has been used to investigate electronic excitations contributing to the superconducting gap function Delta(omega,T) in YBa2Cu3O7-delta. The optical response is strongly peaked at 1.5 eV, and contains two distinct components: one with a characteristic 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 activation energy 2 Delta(0) approximate to 3.5kT(c).