Modulation measurements of YBa2Cu3O7 − δ optical reflectivity using a thermal wave technique

We have measured the differential optical reflectivity (lambda = 0.78 mm) of YBa2Cu3O7-x single crystals in the temperature range of 20-300 K using a thermal wave technique. A sharp signal maximum with a temperature width similar to 10 K was observed below T-c, and was attributed to the electronic contribution of the optical reflectivity. It is concluded that the two components of the differential reflectivity signal are related to accumulation of, the superconducting phase and temperature variation of the electron-scattering time.