Electrical Conductivity of Discontinuous Metal Films

Abstract

We describe investigations into the process of transport at low temperatures in discontinuous metal films. A theoretical analysis using effective medium theory shows that observed temperature dependencies cannot be explained by the conventional model with realistic distributions of relevant parameters. Nor can they be explained by inhomogeneity as is shown by a series of experiments in which the scale of inhomogeneity is measured and shown to be generally much too small. Field-effect measurements show a very small symmetric effect at low temperatures that can only be explained if metal grains are subject to large random potentials. The presence of these potentials is shown directly in another experiment designed to measure the energetics of grain charging. We argue that new models for transport have to be developed which incorporate random potentials as an essential feature.