Tunneling measurements of the electronic density of states of amorphous ${\mathrm{Ge}}_{1-x}{\mathrm{Au}}_x$ near the metal-insulator transition at $x=0.12\mathrm{}$ are reported. In the metallic phase there is a giant zero-bias anomaly with a minimum in the density of states at the Fermi energy. In the insulating phase a pseudogap opens, centered about the Fermi energy, with zero density of states at the Fermi energy.

• Received 17 July 1980

DOI:https://doi.org/10.1103/PhysRevLett.46.556