Observation of rf-induced dc voltages in sputtered binary superconducting films

We have observed that an rf current of frequency 1–5 MHz, passing through a sputtered binary superconducting film, can induce a dc voltage as large as 1 mV across the film for temperatures near the critical temperature T_C. The largest induced voltage has been observed in films which are microscopically inhomogeneous, such as Mo₆₃C₃₇ films which exhibit columnar microstructure. We suggest that the effect may be due to an inverse ac Josephson effect in a randomly connected series array of many microscopic superconducting weak links that are expected to exist close to T_C.