Microwaves-induced oscillations in Andreev tunneling

In the presence of a microwave field the current-voltage characteristics of Au/InO_x/Pb tunnel junctions acquire an oscillatory component that shows up as peaks in the dV/dI vs. V plots. We show that this phenomenon is qualitatively different than the previously reported microwave-induced structure in superconducting devices. While some aspects of the phenomenon resemble photon-assisted tunneling processes, the detailed behavior suggests that it involves destruction of Andreev tunneling.