Edge Reconstruction in a Quantum Spin Hall Insulator

TL;DR

This paper investigates how electron interactions cause edge reconstruction and spin polarization in a quantum spin Hall insulator, revealing a microscopic mechanism that could threaten topological protection.

Contribution

It introduces a microscopic understanding of edge reconstruction driven by interactions in a quantum spin Hall insulator using DMRG simulations.

Findings

Identification of particle-number transitions leading to spin-polarized edges

Edge reconstruction is orbital-selective, mainly in the s-orbital channel

Emergent ferromagnetic exchange stabilizes spin polarization at the edge

Abstract

We study interaction-driven edge reconstruction in a quantum spin Hall insulator described by the Bernevig-Hughes-Zhang model with Kanamori-Hubbard interactions using the real-space density matrix renormalization group method in both the grand-canonical and canonical ensembles. For a two-dimensional cylinder with a smooth edge, we identify discrete particle-number transitions that lead to a spin-polarized edge state stabilized by an emergent ferromagnetic exchange interaction. The reconstruction is orbital-selective, occurring predominantly in the $s$-orbital channel. Our results reveal a fully microscopic mechanism for emergent spin polarization at the edge that could compromise the topological protection of helical edge states by time reversal symmetry.