Density-of-States Anomalies in a Disordered Conductor: A Tunneling Study

Results of single-particle tunneling experiments performed on films of indium oxide are presented. The zero-bias anomalies change character with decreasing thickness from a three-dimensional behavior to a logarithmic energy dependence. Theoretical consideration suggest a crossover from a $\ln V$ to a $V^{\frac{1}{2}}$ correction to the density of states at a thickness-dependent energy. In the $V^{\frac{1}{2}}$ range, where the sample exhibits a three-dimensional density-of-states anomaly, its transport properties may still be two dimensional. These expectations are experimentally confirmed.