Screening of the Coulomb interaction in two-dimensional variable-range hopping

Abstract

A Coulomb gap in the density of states is inferred from variable-range-hopping measurements in two dimensions in a gated GaAs/Al${}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ heterostructure. For large hopping lengths the Coulomb interaction is screened by a metallic gate, and a universal crossover to Mott hopping at low temperatures is observed. Excellent agreement with theory is achieved by adjusting a single combination of constants associated with variable-range hopping. This change in constants is explained by correlated hopping. The Coulomb interaction is not screened by the two-dimensional electron layer.