Quantized resistances in the current-voltage characteristics of superconducting PbAgPb sandwiches

We have compared the voltage steps and the linear current branches in the current-voltage characteristic of PbAgPb sandwiches with numerical results given by a theoretical model due to Kümmel. In this model the occurrence of a potential difference between the film ends is explained by quasiparticle-induced spatial and temporal variations of the superconducting order parameters phase. In these experiments a new feature is found: Also without an external magnetic field the resistance of the current branches are proportional to a quantum number. From this we can draw important conclusions about the shape of the pair potential well and the proximity effect. Furthermore we give an explanation for the temperature dependent hysteresis of the critical current.