Electrostatics of Edge States of Quantum Hall Systems with Constrictions: Metal--Insulator Transition Tuned by External Gates

TL;DR

This paper investigates the electrostatics and edge state behavior in quantum Hall systems with constrictions, explaining the metal-insulator transition and backscattering enhancement through edge splitting into conducting and insulating regions, independent of interedge interactions.

Contribution

It provides a detailed electrostatic model showing that backscattering enhancement arises from edge splitting, not interedge interactions, and analyzes the effects on low-energy edge dynamics and tunneling.

Findings

Backscattering enhancement linked to edge splitting into conducting and insulating stripes.

Conducting channels are widely separated, affecting low-energy edge dynamics.

Interchannel Coulomb interactions do not alter backscattering exponents.

Abstract

The nature of a metal--insulator transition tuned by external gates in quantum Hall (QH) systems with point constrictions at integer bulk filling, as reported in recent experiments of Roddaro et al. [1], is addressed. We are particularly concerned here with the insulating behavior--the phenomena of backscattering enhancement induced at high gate voltages. Electrostatics calculations for QH systems with split gates performed here show that observations are not a consequence of interedge interactions near the point contact. We attribute the phenomena of backscattering enhancement to a splitting of the integer edge into conducting and insulating stripes, which enable the occurrence of the more relevant backscattering processes of fractionally charged quasiparticles at the point contact. For the values of the parameters used in the experiments we find that the conducting channels are widely separated by the insulating stripes and that their presence alters significantly the low-energy dynamics of the edges. Interchannel impurity scattering does not influence strongly the tunneling exponents as they are found to be irrelevant processes at low energies. Exponents of backscattering at the point contact are unaffected by interchannel Coulomb interactions since all channels have same chirality of propagation.