ASYMMETRIC DIFFERENTIAL RESISTANCE OF POINT CONTACTS ON NORMAL-METAL-SUPERCONDUCTOR BILAYERS

Point-contact junctions on normal-metal-superconductor bilayers show a symmetries of different magnitudes and signs in the differential resis tance versus voltage curves for opposite-bias voltages. In the absence of Andreev reflection (i.e. for energies outside the energy gap) no a symmetry is found. The asymmetries are investigated with Ag, Cu, Pd, P t, Ni, and Co as point-contact material on Ag-Pb bilayers. For all mat erials we provide the statistics of the asymmetries. We discuss effect s that may be responsible for this new phenomenon.