Topological Order and Semions in a Strongly Correlated Quantum Spin Hall Insulator

TL;DR

This paper introduces a mean-field approach to explore the effects of strong interactions in a quantum spin Hall insulator, revealing an exotic topologically ordered phase with fractionalized excitations and semionic statistics.

Contribution

It uncovers a novel strongly correlated phase in a quantum spin Hall insulator characterized by topological degeneracy and fractionalized excitations, not previously described.

Findings

Identification of a gapped bulk phase with gapless edge states

Discovery of four-fold topological degeneracy on the torus

Presence of fractionalized excitations with semionic braiding statistics

Abstract

We provide a self-consistent mean-field framework to study the effect of strong interactions in a quantum spin Hall insulator on the honeycomb lattice. We identify an exotic phase for large spin-orbit coupling and intermediate Hubbard interaction. This phase is gapped in the bulk, has gapless edge states and does not break any symmetry. Instead, we find a four-fold topological degeneracy of the ground state on the torus and fractionalized excitations with semionic mutual braiding statistics. Our work highlights the important theme that interesting phases arise in the regime of strong spin-orbit coupling and interactions.