ANOMALOUS CROSSOVER FROM EFROS–SHKLOVSKII TO MOTT VARIABLE RANGE HOPPING IN SILICON MOSFETs

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 = ρ0 exp (T ES /T)1/2 to Mott regime, where ρ = ρ0 exp (T M /T)1/3. With ρ0 is a pre-exponential factor that is found to be close to 2 (h/e2), this crossover occurs when T ~ 1 K .