Anomalous crossover from efros-shklovskii to mott variable range hopping in silicon mosfets

摘要

In this paper, we investigate the temperature dependence of the electrical resistivity of a two-dimensional electron system in n-channel Si-MOSFETs at zero magnetic field down to 0.2 K. At low electron densities, near the metal-insulator transition point from the insulating side, our results show the existence of a crossover, from Efros-Shklovskii variable range hopping (ES-VRH), which is consistent with the existence of a Coulomb gap, where ρ = ρ_0exp(T_(ES)/T)~(1/2) to Mott regime, where ρ = ρ_0exp(T_M/T)~(1/3). With ρ_0 is a pre-exponential factor that is found to be close to 2 (h/e~2), this crossover occurs when T ～ 1 K.