Investigation of Microwave-Induced dc Voltages across Unbiased Josephson Tunnel Junctions

We have studied the power dependence of the microwave-induced dc voltages across "unbiased" Pb—Pb oxide—Pb Josephson tunnel junctions and found a systematic dependence. We have also found that the Josephson effect in the form of induced quantum voltages was observable in a large dc magnetic field as high as 0.5 kG, about one-half of the $H_{c2\mathrm{}}$ of the superconducting Pb film.