METAL-INSULATOR-TRANSITION IN THIN TIOX FILMS

Conductivity and electron tunneling measurements are reported for amorphous, oxygen rich Ti films in the vicinity of the Anderson metal-insulator transition. In the metallic films the conductivity varies proportional to square-root T, while for the insulating films the Mott variable range hopping process is recovered. By reducing the film thickness, a cross-over towards a two-dimensional behavior is observed. For the metallic films a ln T divergence of the resistance occurs at the lowest temperatures. On the other hand, the two-dimensional hopping process is affected by the presence of a Coulomb gap. Our tunneling measurement provide us with a quantitative estimate for the reduction of the density of states in metallic films due to the disorder enhanced Coulomb repulsion.