Abstract
Presents a detailed analysis of conduction in discontinuous metals in the regime of activated conductivity. It is shown that the effective conductance between a pair of metallic grains at low temperature may be expressed as exp(-(2 alpha R+E/kT)) where R is the grain separation and E is an effective activation energy related to the energies for localisation of a single charge on the two grains. Effective-medium theory is then used to obtain the temperature dependence of the bulk conductivity for realistic distributions of R and E. It is shown that near-neighbour tunnelling cannot explain observed behaviour if there is no correlation between grain size and separation. This leads to the conclusion that there is currently no detailed model that gives a satisfactory general explanation for conduction in such systems. Possible bases for a general theory are discussed briefly.