Phonon-injection-induced nonequilibrium phenomena in superconducting proximity-effect bridges

Extensive investigations of the current-voltage characteristics of long Ag-Sn proximity-effect bridges when phonons are dc injected from heated transverse normal metal strips show that at bath temperatures above Tsub(lambda) (the lambda point of 4He) the experimentally observed critical current dependence on in ector current deviates from a simple heating model in a direction consistent with Parker's modified heating theory of nonequilibrium superconductors whereas below Tsub(lambda) the deviation changes direction. However, the injection induced transition is continuous. Further below Tsub(lambda), bridges underlaid with a thin film of germanium exhibit a first-order transition to the normal state which is consistent with the Owen-Scalapino model for nonequilibrium superconductors. Possible implications are discussed. (auth.)