CHARGE-TRANSPORT IN SUPERCONDUCTOR SEMICONDUCTOR/NORMAL-CONDUCTOR STEP JUNCTIONS/

We present experimental data on the transport properties of a two-dime nsional electron gas in contact with a superconducting and a normal co nducting electrode. A short distance (approximate to 500 nm) between t he electrodes is realized by means of a step geometry. At voltages bel ow the gap voltage of the superconductor, a decrease in resistivity of about 10% is observed. At low temperature and for voltages correspond ing to a value smaller than the Thouless energy, an enhancement of the resistance is observed. The resistance at low energy coincides approx imately with the resistance value above the gap voltage and depends se nsitively on the bias current, temperature, and magnetic field. The ex perimental results are compared to theories of the reentrance effect. For small energies, good agreement is found.