Duality, the Semi-Circle Law and Quantum Hall Bilayers

TL;DR

This paper investigates the implications of an approximate discrete symmetry in Quantum Hall systems, predicting universal behaviors, phase transitions, and semicircular conductivity trajectories, especially in bilayer and spin-degenerate systems.

Contribution

It extends the understanding of quantum Hall phase transitions by analyzing duality and semicircle laws in bilayer and spin-degenerate systems, predicting new phases and specific conductivity trajectories.

Findings

Predicted semicircular trajectories in bilayer conductivities.

Identified new phases in quantum Hall bilayer systems.

Established universality and selection rules for phase transitions.

Abstract

There is considerable experimental evidence for the existence in Quantum Hall systems of an approximate emergent discrete symmetry, $\Gamma_0(2) \subset SL(2,Z)$. The evidence consists of the robustness of the tests of a suite a predictions concerning the transitions between the phases of the system as magnetic fields and temperatures are varied, which follow from the existence of the symmetry alone. These include the universality of and quantum numbers of the fixed points which occur in these transitions; selection rules governing which phases may be related by transitions; and the semi-circular trajectories in the Ohmic-Hall conductivity plane which are followed during the transitions. We explore the implications of this symmetry for Quantum Hall systems involving {\it two} charge-carrying fluids, and so obtain predictions both for bilayer systems and for single-layer systems for which the Landau levels have a spin degeneracy. We obtain similarly striking predictions which include the novel new phases which are seen in these systems, as well as a prediction for semicircle trajectories which are traversed by specific combinations of the bilayer conductivities as magnetic fields are varied at low temperatures.