Electron conduction within Landau level tails of medium-mobility GaAs / AlGaAs heterostructures

TL;DR

This study investigates electron conduction in Landau level tails of GaAs/AlGaAs heterostructures, revealing activated conductivity and field-assisted tunneling effects influencing the quantum Hall regime at temperatures above 4.2 K.

Contribution

It demonstrates the presence of variable range hopping and tunneling effects in medium-mobility heterostructures, expanding understanding of conduction mechanisms in quantum Hall systems.

Findings

Activated conductivity with energies scaling with cyclotron energy

Additional tunneling contribution enhances conductivity at low temperatures

Hopping conduction persists above 4.2 K

Abstract

The temperature dependence of both components of the resistivity tensor $\varrho_{xx}(T)$ and $\varrho_{xy}(T)$ has been studied at T $\geq$ 4.2 K within IQHE plateaux around filling factors \nu=2 and \nu=4 of medium- -mobility GaAs/AlGaAs heterostructures. In the middle of the mobility gap standard activated conductivity has been found with activation energies $\Delta $ scaling well with $\hbar\omega_{c} / 2$ . At filling factors slightly below $\nu$=2 another contribution adds to the activated conductivity at T $\leq$ 12 K. This additional contribution can be further enhanced at higher mesuring d.c. currents.We suggest, that it arises due to enhanced electric field assisted tunneling across potential barriers separating localized states within the bulk of the sample.This effect contributes to the backscattering across the sample leading to an enhanced longitudinal conductivity. The additional contribution to $\sigma_{xx}(T)$ can be reasonably well fitted to the formula for the variable range hopping in strong magnetic fields indicating that the hopping can persist even at temperatures well above 4.2K.