Nonequilibrium superconductivity

In general, the quasiparticles, phonons, and pair field in a superconductor driven by an external source are out of equilibrium. Here we review briefly the various quasiparticle and phonon lifetimes in real metals and estimate the strengths necessary to induce a strongly nonequilibrium state. Then we investigate the properties of a thin film driven in a spatially uniform steady state by quasiparticle injection, heater phonon pumping, and microwave radiation. This analysis uses a set of coupled kinetic equations for quasiparticle and phonon distributions and the BCS gap equation with the self-consistently determined quasiparticle distribution. Such films can be used to generate phonons with energy near 2 . In addition, the gap enhancement in a thin film due to microwave irradiation is discussed.Work supported by the Office of Naval Research. Preliminary results have been reported at the Applied Superconductivity Conference, Stanford, August 1976 IEEE Trans. Magn. MAG-13, 747 (1977)] and at the NATO Advanced Study Institute at Lago di Garda, Italy, September 1976 NATO Adv. Study Inst. Series (B-Physics) 21, 447–486 (1977)].J. S. Guggenheim Foundation Fellow (1976–77).