Conduction in granular metals-the effect of the grain separation distribution

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Abstract
A charging energy model of conduction in granular metals has been considered. It has been shown that the temperature dependence of the DC conductivity, sigma approximately exp(-(T1/T)12/), interpreted as a crossover between high- and low-temperature behaviour can in fact be explained as resulting from flat parts of both the density of states and the distribution of tunnelling distances. It has also been shown that such distributions can appear in real metal-insulator composites. Models of hopping conduction in regular lattices and in continuous systems of hard and soft grains have been proposed. A comparison with experiments has been given as well.