LOW-TEMPERATURE OPTICAL-RESPONSE OF A SINGLE GRAIN-BOUNDARY IN SUPERCONDUCTING YBA2CU3O7-DELTA THIN-FILM

We have investigated the optical response from a single grain boundary in a thin film (approximately 300 nm) of superconducting YBa2Cu3O7-de lta fabricated on bicrystals SrTiO3 substrate. We have studied the tem perature, bias current, and magnetic field dependence of the optical r esponse in the temperature range of 15 K less-than-or-equal-to T less- than-or-equal-to 35 K. We find that the optical response from the sing le grain boundary in this temperature range can be satisfactorily expl ained in terms of the optical response of a Josephson weak link. The o ptical response of the grain boundary is qualitatively similar to that of granular films seen in the earlier studies, indicating that the la tter may be dominated by the optical response of grain-boundary weak l inks.