Active subclusters in percolative hopping transport

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Abstract
In materials exhibiting localized states due to disorder or due to impurity sites, the standard model for transport is the random-resistance network with an exponentially wide distribution of resistances. dc currents are carried on paths where the largest resistance is as small as possible, but the paths exist on clusters of resistors that percolate across the sample. This model differs from common percolative transport where equal resistors are found in randomly placed bonds on a lattice. In such systems transport is usually most active on the backbone subcluster of the percolation cluster. We believe that transport in the random-resistance network actually occurs on an essentially different current-carrying subcluster. We study some of the properties of this subcluster using a computer model. These properties are important for understanding various transport phenomena in impurity conduction, conducting polymers, amorphous semiconductors, and a variety of other disordered solids.