Femtosecond dynamics of quasi-particles in YBa/sub 2/Cu/sub 3/O/sub 7- delta / superconductor films

The transient electronic response of epitaxially grown YBa/sub 2/Cu/sub 3/O/sub 7- delta / superconductor thin films in the femtosecond time domain was investigated using transient photoinduced reflectivity ( Delta R) with 60-fs time resolution. For temperatures T>T/sub c/, only a bolometric signal was observed with Delta R>0. For T0. The results for T