We have investigated the optical response of epitaxial ultrathin (3 nm) YBa2Cu3O7-δ film on NdGaO3 substrate and thin (50 nm) film of YBa2Cu3O 7-δ on a bicrystal SrTiO3 substrate. While the current-voltage characteristics of the ultrathin film indicate a Kosterlitz-Thouless transition (associated with vortex-antivortex unbinding) at a temperature TKT, we do not observe any optical response at or below TKT. An enhanced optical response with nonbolometric characteristics was observed from the grain-boundary as compared to the bolometric optical response of the epitaxial film at the resistive transition. These results indicate that the grain-boundary weak links play a significant role in the enhanced optical response near Tc.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy (miscellaneous)