Quantum-percolation model of electronic transport in two-dimensional granular metal films.

Abstract

We study the macroscopic and mesoscopic transport properties of granular metal films by using a quantum-percolation model. A granular metal film with metal fraction p is simulated by conducting grains randomly occupying the sites of a square lattice with probability p. Electrons are allowed to hop between nearest-neighbor grains. This model incorporates the granular property of a film and enables us to study the magnetoconductance in both the weak- and strong-scattering regimes. The calculated magnetoconductance exhibits a sign change as the temperature varies, as well as oscillations as a function of the applied magnetic field. Both are consistent with some recent experimental data. The universal conductance fluctuations and resonant-tunneling characteristics are also studied systematically in both the extended and the localized regimes of mesoscopic samples. At the percolation threshold, the localization behavior is studied by using both the finite-size-scaling method and the resonant-tunneling method. Our results show no evidence for superlocalization. The effect of a magnetic field on localized wave functions at the percolation threshold is also examined.