Radiation detection by coherent Josephson phenomena in agglomerated tin films
We have previously reported radiant energy detection by superconducting thin films in both a thermal (or bolometer) mode and a current mode. We now report evidence that at least some current-mode detection is due to Josephson behavior associated with agglomeration in tin films. The temperature dependence of the critical current agrees with results for Dayem bridges, and we observe microwave-induced steps in the current-voltage characteristics which have the proper dependence on frequency and power. At a constant film resistance the current-mode responsivity shows structure (dips) in its dependence on bias current which shifts with microwave frequency in agreement with the Josephson theory. The films appear to behave like an array of weak links in the "correlated" state as observed by Clark and explained by him and Tilley.