Low frequency noise properties of all-thin film superconducting point contacts

We report the results of low frequency voltage noise measurements of an all-thin film superconducting point contact (SPC). The SPC is prepared in liquid helium by application of a voltage pulse to a Nb-MgO-NbN edge sandwich. Increasing the amplitude of the pulse we may observe a gradual transition of a junction from the tunneling to metallic transport regime. We study the magnitude of low frequency noise during this transition and find that noise decreases quickly with decreasing ratio of subgap-to-supergap resistance. This result is contrasted with an opposite finding of C. T. Rogers and R. A. Buhrman [IEEE Trans. Magn. MAG-21, 126 (1985)] for the limit of a ‘‘leaky’’ tunnel junction. This comparison suggests that the excess subgap conductivity observed in our samples is caused by an Andreev reflection.