Charge transport in superconductor/semiconductor/normal-conductor step junctions

Abstract

We present experimental data on the transport properties of a two-dimensional electron gas in contact with a superconducting and a normal conducting electrode. A short distance (\ensuremath{\approx}500 nm) between the electrodes is realized by means of a step geometry. At voltages below the gap voltage of the superconductor, a decrease in resistivity of about 10% is observed. At low temperature and for voltages corresponding to a value smaller than the Thouless energy, an enhancement of the resistance is observed. The resistance at low energy coincides approximately with the resistance value above the gap voltage and depends sensitively on the bias current, temperature, and magnetic field. The experimental results are compared to theories of the reentrance effect. For small energies, good agreement is found.