Nonequilibrium carrier transport in superconducting niobium-silicon heterostructures

Abstract
Carrier transport through a 50-nm-thick single-crystal silicon film sandwiched between two superconducting electrodes is studied. A strongly voltage-dependent normal current is found, substantially below the value in the normal state, together with the structure at submultiples of the superconducting energy gap. The results are explained as a hot-electron effect, taking into account elastic and Andreev scattering at the interfaces and ignoring energy relaxation in the silicon. It is argued that the elastic scattering at the interfaces is due to Fermi-momentum mismatch.