EVIDENCE FOR 2-COMPONENT SUPERCONDUCTIVITY IN THE FEMTOSECOND OPTICALAND TRANSIENT PHOTOCONDUCTING RESPONSE OF YBA2CU3O7-DELTA

Femtosecond time-resolved spectroscopy and transient photoconductivity measurements have been used to investigate the time-dynamics, frequen cy dependence and symmetry of electronic excitations associated with t he opening of the superconducting gap in YBa2Cu3O7-delta. Two clearly identifyable relaxation components are observed operative on nanosecon d and picosecond timescales respectively, implying the co-existence of localized states and band-like carriers both in the superconducting a nd normal state. From the temperature dependence of the two components it is clear that both relaxation phenomena are directly connected wit h the formation of the superconducting condensate. The spectral respon se for both excitations closely follows the spectrum observed in therm al modulation spectroscopy and implies that the electron-boson couplin g function includes a charge-transfer component at optical excitation energies in the region of 1.5-2 eV.