Gap suppression by self-injection of quasiparticles in tin-tin-oxide-tin tunnel junctions

A decrease of the superconducting energy gap has been observed in high-current-density tin-tin-oxide-tin tunnel junctions. This effect cannot be adequately accounted for by simple heating and is attributed to the presence of a nonequilibrium excess quasiparticle population created by the tunnel current. Analysis using a phenomenological model of the nonequilibrium superconductor yields a determination of the phonon-trapped quasiparticle recombination lifetime in tin in good agreement with the results of other experiments. A size-dependent enhancement of the phonon-emission efficiency of very narrow tunnel junctions is also observed and explained. © 1978 The American Physical Society.