Tunneling-current-induced transitions of superconducting thin films

The resistive state of a superconducting film can be induced either by passing sufficient current along the film or by raising the temperature above Tc. We have been studying this transition in aluminum films when they are injected with "hot" (i.e. nonthermal) phonons and electrons. This injection efficiently breaks electron pairs in the region near the injection point. These "hot", electrons and phonons are produced by tunnel junctions which incorporate or are adjacent to the Al film under study. This method of current injection usually results in significantly lower critical currents than the critical current measured conventionally along the film. Well-defined and reproducible critical currents together with I-V traces for the Al film, which under certain conditions are characterized by a series of constant current voltage steps, have been obtained with a variety of geometrical configurations and different tunnel junction resistances.