Conduction in Granular Metals by Hopping via Virtual States

It is shown that the conductivity of granular metals on the insulating side of the metal--insulator transition can be essentially determined by inter-grain tunneling via virtual localized states of intermediate grains. This mechanism gives rise to conductivity temperature dependence of the form ln(sigma)=const-(T0/T)^x, where x is about 0.4, and to a large enhancement of the conductivity.