Optical absorption and disorder in an amorphous metal

The optical gap ${\mathit{E}}_{\mathit{g}}$ of amorphous indium oxide films is measured as a function of static disorder characterized by the dimensionless conductivity g. In the range 1≥g≥0.1 the optical gap obeys a scaling relation: Δ${\mathit{E}}_{\mathit{g}}$=-${\mathit{E}}_{\mathrm{*}}$Δg where ${\mathit{E}}_{\mathrm{*}}$ is of the order of the Fermi energy of the given sample. These results are ascribed to the continuous shift of the mobility edge in the conduction band with disorder.