Tunneling and Percolation in Metal-Insulator Composite Materials

TL;DR

This paper explains how tunneling and percolation coexist in metal-insulator composites, showing that the percolation cluster is formed by nearest-neighbor tunneling, reconciling tunneling with percolation theory.

Contribution

It reveals that the apparent cut-off of tunneling to non-nearest neighbors causes the percolation behavior in composites, linking tunneling networks to percolation clusters.

Findings

Percolation cluster is the nearest-neighbors sub-network of tunneling.

Cut-off of tunneling to non-nearest neighbors explains percolation behavior.

Atomic force microscopy measurements support the model.

Abstract

In many composites the electrical transport takes place only by tunneling between isolated particles. For a long time it was quite a puzzle how, in spite of the incompatibility of tunneling and percolation networks, these composites conform well to percolation theory. We found, by conductance atomic force microscopy measurements on granular metals, that it is the apparent cut-off of the tunneling to non-nearest neighbors that brings about this behavior. In particular, the percolation cluster is shown to consist of the nearest-neighbors sub-network of the full tunneling network.