Coulomb drag in high Landau levels

TL;DR

This paper develops a diagrammatic theory explaining surprising experimental results of Coulomb drag in high Landau levels, including negative drag and non-monotonous temperature dependence, by analyzing particle-hole asymmetry sources.

Contribution

It introduces a systematic diagrammatic approach to Coulomb drag in strong magnetic fields, accounting for both diffusive and ballistic regimes, with focus on the ballistic regime relevant to experiments.

Findings

Coulomb drag can become negative in high Landau levels.

Temperature dependence of drag shows a sharp peak at Landau level width.

Drag is influenced by two particle-hole asymmetry sources: dispersion curvature and Landau quantization.

Abstract

Recent experiments on Coulomb drag in the quantum Hall regime have yielded a number of surprises. The most striking observations are that the Coulomb drag can become negative in high Landau levels and that its temperature dependence is non-monotonous. We develop a systematic diagrammatic theory of Coulomb drag in strong magnetic fields explaining these puzzling experiments. The theory is applicable both in the diffusive and the ballistic regimes; we focus on the experimentally relevant ballistic regime (interlayer distance $a$ smaller than the cyclotron radius $R_c$). It is shown that the drag at strong magnetic fields is an interplay of two contributions arising from different sources of particle-hole asymmetry, namely the curvature of the zero-field electron dispersion and the particle-hole asymmetry associated with Landau quantization. The former contribution is positive and governs the high-temperature increase in the drag resistivity. On the other hand, the latter one, which is dominant at low $T$, has an oscillatory sign (depending on the difference in filling factors of the two layers) and gives rise to a sharp peak in the temperature dependence at $T$ of the order of the Landau level width.