Scaling of the insulator-to-superconductor transition in ultrathin amorphous Bi films

Study of the electrical conductances of a series of ultrathin Bi films as a function of increasing thickness has revealed behavior which can be correlated with the onset of superconductivity, even in the insulating state. The conductances of these films scale empirically with a single parameter which falls to zero when the films become superconductive. These observations suggest a direct transition between insulating and superconducting behavior. This transition occurs at a normal-state sheet resistance close to the quantum resistance for pairs, Rq=h/4e².