SIMULATION OF BELOW-GAP PHOTORESPONSE OF THIN-FILM SUPERCONDUCTORS BY JOSEPHSON-JUNCTION ARRAYS

The below-gap, nonbolometric photoresponse of granular, thin-film superconductors seen recently by Strom et al. and by other experimental groups is simulated by a numerical study of the dc voltage response to an applied ac current at finite temperature, by ordered and disordered two-dimensional arrays of resistively shunted Josephson junctions. The current-assisted random generation of vortex-antivortex pairs by the temperature fluctuations and the ac current is observed. The photoresponse for perfect arrays shows a large peak at the Kosterlitz-Thouless transition T(KT) which moves to lower temperature with increasing I(dc) or I(ac). For randomly diluted, disordered arrays at p = 0.9 (10% of the junctions removed) the peak in the photoresponse is greatly enhanced and moved to lower temperatures. The behavior of the photoresponse versus bias current, ac power, and frequency is reported. A simple model of random localized heating is tried as a numerical approach to explain some features of the above-gap photoresponse.