SIMULATION OF BELOW-GAP PHOTORESPONSE OF THIN-FILM SUPERCONDUCTORS BYJOSEPHSON-JUNCTION ARRAYS

The below-gap, nonbolometric photoresponse of granular, thin-film supe rconductors seen recently by Strom et al. and by other experimental gr oups is simulated by a numerical study of the dc voltage response to a n 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 photoresp onse 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 enhan ced and moved to lower temperatures. The behavior of the photoresponse versus bias current, ac power, and frequency is reported. A simple mo del of random localized heating is tried as a numerical approach to ex plain some features of the above-gap photoresponse.