Experimental Determination of the Quasiparticle Energy Distribution in a Nonequilibrium Superconductor

Abstract

We have observed sharp structure in the $I\ensuremath{-}V$ characteristics of Al-$\mathrm{Al}{\mathrm{O}}_{x}$-PbBi tunnel junctions induced by tunnel injection of excess quasiparticles into the Al film. Interpretation of this structure provides information on the form of the steady-state quasiparticle energy distribution, showing that it is highly nonthermal. The data also demonstrate the presence of a branch imbalance in the injected Al film.