Shot noise properties of superconducting quasiballistic contacts

Experiment and analysis have been done to show that the low frequency voltage noise properties of a current-biased Nb-(constrictions)-NbN (S-c-S´) contacts is well described by existing theories of a mesoscopic two-terminal conductor. The quasiparticle characteristics of the S-c-S´ which has adjustable current-voltage curve is also well analyzed using the theory based on the single Andreev reflection model without heating. In the clean S-c-S´ contacts, there is no measurable excess noise contribution associated with the Andreev reflection itself.