Interaction of ac Josephson Currents with Surface Plasmons in Thin Superconducting Films

The coupling of low-frequency surface plasmons to the ac Josephson currents in superposed thin dielectric and superconducting metal films is examined. The $I-V$ characteristics for various superposed film systems are derived. The theory permits the magnitude of the parameters entering in the expression for the $I-V$ characteristics, as well as their dependence on various quantities (temperature, mean free path, etc.), to be determined and compared with existing experiments. We have extended the theory of steplike structures in the $I-V$ characteristics of a single Josephson junction to multiple films, and have found that more than one series of such steplike structures is possible. The theory provides a natural explanation for a three-film tunneling experiment of Giaever. Finally, the modifications of the dispersion relations for surface plasma oscillations in multiple-film systems, when admitting the presence of the ac Josephson effect, are derived.