rf-induced effects in superconducting tunnel junctions

Arguments are presented to resolve experimental discrepancies with the theory of photon-assisted tunneling. A standing-wave model is suggested as a more realistic picture of the rf fields in a thin-film tunnel junction. By including the effects of this model in the theories of Tien and Gordon and of Werthamer, we obtain qualitative agreement with data on both the Josephson effects and the photon-assisted tunneling effects in the same junction. In an experiment with a junction sufficiently small to maintain a uniform rf field, we find excellent agreement with the unmodified theory. The low-frequency equivalence of the photon-assisted tunneling phenomenon and classical rf detection is also pointed out and used to demonstrate that the magnitude of the rf voltage appears correctly in the theory. We conclude that the Werthamer theory of rf-induced effects in superconducting tunnel junctions is on very firm experimental ground.