Nonbolometric optical response of YBa2Cu3O7−δ epitaxial films

Abstract

The optical response of high-quality epitaxial ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ films on ${\mathrm{LaGaO}}_3$ and ${\mathrm{SrTiO}}_3$ substrates is reported. A careful analysis of the results reveals a strong nonbolometric response at temperatures below the onset of the superconducting transition. This finding is in contrast with recently published reports which attribute the optical response of epitaxial films to a bolometric effect only. We interpret this response as due to photoenhanced flux creep in the superconducting films.