Electronic correlation effects and the Coulomb gap at finite temperature

We have investigated the effect of the long-range Coulomb interaction on th e one-particle excitation spectrum of n-type germanium, using tunneling spe ctroscopy on mechanically controllable break junctions. At low temperatures , the tunnel conductance shows a minimum at zero bias voltage due to the Co ulomb gap. Above 1 K, the gap is filled by thermal excitations. This behavi or is reflected in the variable-range hopping resistivity measured on the s ame samples: up to a few degrees Kelvin the Efros-Shklovskii InR proportion al to T-1/2 law is obeyed, whereas at higher temperatures deviations from t his law occur. The type of crossover differs from that considered previousl y in the literature.