Anyon superfluidity of excitons in quantum Hall bilayers

TL;DR

This paper proposes the concept of anyonic exciton superfluidity in quantum Hall bilayers, where neutral anyons with fractional statistics form a superfluid state, revealing rich topological and symmetry-breaking phenomena.

Contribution

It introduces the idea of anyonic exciton superfluidity in quantum Hall bilayers and analyzes its properties near topological phase transitions using Chern-Simons QED3.

Findings

Finite density of anyonic excitons can form a superfluid with specific topological order.

Superfluid stiffness scales as | u|^{1/2} near layer imbalance transitions.

Spatial symmetry breaking driven by an underlying composite Fermi surface is prevalent.

Abstract

The charged anyons of a fractional quantum Hall fluid are necessarily dispersionless due to the continuous magnetic translation symmetry. Neutral anyons, however, can disperse, resulting in a much richer space of possible ``daughter'' states when doped to finite density. We discuss a natural realization of such physics in quantum Hall bilayers, where a finite density of excitons with fractional statistics is argued to give rise to `anyonic exciton superfluidity,' the charge-neutral analog of anyon superconductivity. In a balanced bilayer of two Laughlin $\nu = 1/3$ states, the minimal interlayer exciton carries anyonic exchange statistics. A finite density of these excitons is argued to yield an exciton superfluid stitched to a specific bulk topological order and edge spectrum. Such superfluidity should be most robust near the direct transition into the Halperin $(112)$ state, and near analogous transitions in the bilayer Jain sequence at total filling $\nu_\text{T} = 2\times \frac{n}{2n+1}$. These topological transitions can be described by Chern-Simons QED$_3$, from which we derive several novel and general properties of anyon superfluidity near such transitions, including an anomalously large superfluid stiffness of $\kappa_\text{s} \propto |\delta\nu|^{1/2}$ at layer imbalance fraction $\delta\nu$. A notable feature of the phase diagrams we construct is the prevalence of spatial symmetry breaking, driven by an underlying composite Fermi surface. Our results can be directly tested with currently available experimental techniques. We compare our theory with existing data and make concrete predictions for future measurements, including higher-pseudospin exciton superfluids when doping higher Jain fractions.