Temperature-dependent disorder and magnetic field driven disorder: experimental observations for doped GaAs/AlGaAs quantum well structures

TL;DR

This study investigates how temperature and magnetic fields influence disorder in doped GaAs/AlGaAs quantum wells, revealing complex conductance behaviors linked to charge redistribution and localized states.

Contribution

It provides experimental observations and a detailed theoretical model explaining temperature and magnetic field effects on disorder in doped quantum well structures.

Findings

Non-monotonic temperature dependence of conductance around 100 K

Strong negative magnetoresistance at low temperatures

Suppression of magnetoresistance with increasing temperature

Abstract

We report experimental studies of conductance and magnetoconductance of GaAs/AlGaAs quantum well structures where both wells and barriers are doped by acceptor impurity Be. Temperature dependence of conductance demonstrate a non-monotonic behavior at temperatures around 100 K. At small temperatures (less than 10 K) we observed strong negative magnetoresistance at moderate magnetic field which crossed over to positive magnetoresistance at very strong magnetic fields and was completely suppressed with an increase of temperature. We ascribe these unusual features to effects of temperature and magnetic field on a degree of disorder. The temperature dependent disorder is related to charge redistribution between different localized states with an increase of temperature. The magnetic field dependent disorder is also related by charge redistribution between different centers, however in this case an important role is played by the doubly occupied states of the upper Hubbard band, their occupation being sensitive to magnetic field due to on-site spin correlations. The detailed theoretical model is present.