Correlated hopping through thin disordered insulators

We present data from Mo/a-Si/Mo tunnel junctions together with calculations that show that hopping transport via localized states in amorphous silicon is highly correlated. Localized states whose single-particle energies lie well below the Fermi level participate in transport due to the large on-site Coulomb interaction U. The results also imply that the density of these states is roughly constant over a wide energy range of order U.