On the Coulomb interaction in granular systems

The previous theories on the behaviour of the conductivity of high-resistivity granular metals are analysed in terms of the Coulomb interaction between the charge carriers. In these theories a non-interacting system of carriers is considered, but it turns out that the Coulomb interaction is involved elsewhere in the calculations. Leaving out this interaction is shown to be a rather wrong assumption. The application of the Efros-Shklovskii theory leads to a real Coulomb gap. A second method is used to confirm the existence of this gap, which width is determined. The results we obtain seem to be consistent with those obtained on the systems with impurities.