Electron Assisted Variable Range Hopping in Strongly Correlated 2D Electron Systems

Abstract

We have investigated the temperature dependence of longitudinal resistivity of high mobility two dimensional (2D) electron systems in the strongly correlated regime (rs ∼ 4–5). The area of the samples was relatively small, typically 2 × 2 μm2. The resistivity followed an Efros–Shklovskii (ES)-type variable range hopping (VRH) behavior, ϱ (T) = ϱ0 exp (T0/T)p, with p = 0.5. We found that in this regime, the pre-factor ϱ0 increases by discrete steps of h/2e2 as the carrier concentration (n) is increased, starting from ϱ0 = h/e2 at the lowest values of n close to the localization. The jumps in ϱ0 were associated with an oscillation in the activation energy defined by T0. We have discussed the observation of such quantized, temperature-independent resistivity pre-factors in the framework of electron assisted VRH.