Coulomb tunneling anomaly in disordered copper-germanium alloys

We have performed electronic tunneling density of states and resistivity measurements in three-dimensional Cu_xGe_100-x films spanning the weakly and strongly localized regimes. We found that the Coulomb anomaly in tunneling density of states in the strongly disordered regime is very profound and grows in strength with resistivity. However, when the system becomes less disorderly and approaches the weakly disordered regime, this anomaly weakens rapidly. The data suggest that the disorder enhanced electron-electron interaction effects can drive the crossover from weak disorder to strong disorder in CuGe alloy system.