Vortex states of a disordered quantum Hall bilayer

TL;DR

This paper models vortex configurations in disordered quantum Hall bilayers, predicting a transition from rare to proliferating vortices with increasing disorder, affecting counterflow current decay and tunneling behavior.

Contribution

It introduces a model for vortex states in disordered quantum Hall bilayers and predicts a disorder-driven vortex proliferation transition affecting transport properties.

Findings

Vortex proliferation occurs above a critical disorder strength.

Counterflow current decay length increases significantly in the strong-disorder regime.

Suppression of counterflow current leakage explains experimental observations.

Abstract

We present and solve a model for the vortex configuration of a disordered quantum Hall bilayer in the limit of strong and smooth disorder. We argue that there is a characteristic disorder strength below which vortices will be rare, and above which they proliferate. We predict that this can be observed tuning the electron density in a given sample. The ground state in the strong-disorder regime can be understood as an emulsion of vortex-antivortex crystals. Its signatures include a suppression of the spatial decay of counterflow currents. We find an increase of at least an order of magnitude in the length scale for this decay compared to a clean system. This provides a possible explanation of the apparent absence of leakage of counterflow currents through interlayer tunneling, even in experiments performed deep in the coherent phase where enhanced interlayer tunneling is observed.