ELECTRON-TUNNELING EXPERIMENTS NEAR THE METAL-INSULATOR-TRANSITION

Tunneling measurements of the electronic density of states N(E) on amorphous Ge1-xCr(x) and Si1-xCr(x) near the metal-insulator transition are reported. N(E) shows a square-root law in the energy dependence on the metallic side. The results are interpreted in terms of the electron-electron interaction in disordered materials. The range of the E1/2 dependence is the same for all chromium concentrations in each material. An E1/2 dependence can be seen for higher energies on the insulating side as well. Temperature dependent contributions to N(E) should be relevant only for energies smaller than 5 k(B)T.