The physical picture behind the oscillating sign of drag in high Landau levels

TL;DR

This paper explains the oscillating sign of drag resistivity in high Landau levels by analyzing how disorder affects electron displacement during momentum transfer, linking it to experimental observations in quantum Hall systems.

Contribution

It introduces a physical model connecting disorder-induced Landau level mixing to the sign oscillations of drag resistivity in quantum Hall regimes.

Findings

Disorder causes large, energy-dependent displacements affecting drag sign.

Oscillations vanish with smooth disorder and localized states.

The model explains experimental temperature and sign behavior.

Abstract

We consider the oscillating sign of the drag resistivity and its anomalous temperature dependence discovered experimentally in a bi-layer system in the regime of the integer quantum Hall effect. We attribute the oscillating sign to the effect of disorder on the relation between an adiabatic momentum transfer to an electron and the displacement of its position. While in the absence of any Landau level mixing a momentum transfer $\hbar \bf q$ implies a displacement of $ql_H^2$ (with $l_H$ being the magnetic length), Landau level mixing induced by short range disorder adds a potentially large displacement that depends on the electron's energy, with the sign being odd with respect to the distance of that energy from the center of the Landau level. We show how the oscillating sign of drag disappears when the disorder is smooth and when the electronic states are localized.