The microscopic nature of localization in the quantum Hall effect

TL;DR

This paper investigates the microscopic nature of localization in the quantum Hall effect, revealing that Coulomb interactions significantly influence localized states and challenge the traditional single-particle theory.

Contribution

The study provides experimental evidence that Coulomb interactions dominate localized states, extending understanding beyond the single-particle framework in quantum Hall systems.

Findings

Localized states are primarily determined by Coulomb interactions.

Localized states appear only when kinetic energy quantization limits screening.

The quantum Hall effect exhibits more diverse regimes than single-particle theory predicts.

Abstract

The quantum Hall effect arises from the interplay between localized and extended states that form when electrons, confined to two dimensions, are subject to a perpendicular magnetic field. The effect involves exact quantization of all the electronic transport properties due to particle localization. In the conventional theory of the quantum Hall effect, strong-field localization is associated with a single-particle drift motion of electrons along contours of constant disorder potential. Transport experiments that probe the extended states in the transition regions between quantum Hall phases have been used to test both the theory and its implications for quantum Hall phase transitions. Although several experiments on highly disordered samples have affirmed the validity of the single-particle picture, other experiments and some recent theories have found deviations from the predicted universal behaviour. Here we use a scanning single-electron transistor to probe the individual localized states, which we find to be strikingly different from the predictions of single-particle theory. The states are mainly determined by Coulomb interactions, and appear only when quantization of kinetic energy limits the screening ability of electrons. We conclude that the quantum Hall effect has a greater diversity of regimes and phase transitions than predicted by the single-particle framework. Our experiments suggest a unified picture of localization in which the single-particle model is valid only in the limit of strong disorder.