Photoemission study of the transition from the insulating to metallic state in ultrathin layers

The transition from the insulating to metallic state in ultrathin Pb films was studied using high-resolution photoemission. The states near ${\mathrm{E}}_{\mathrm{F}}$ were probed as Pb was deposited onto a thin insulating layer, thin enough to reduce macroscopic charging. The results, which experimentally show a vanishing of states at ${\mathrm{E}}_{\mathrm{F}}$, are consistent with the arguments of Efros and Shklovskii based on electron-electron interactions, and as far as we know are the first in situ study of the electronic properties as one goes from the insulating to metallic state in a two-dimensional system.