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Edge Reconstruction in a Quantum Spin Hall Insulator

Rahul Soni1,2, Matthias Thamm3, Gonzalo Alvarez4, Bernd Rosenow3, and Adrian Del Maestro1,2,5

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Phys. Rev. Lett. 136, 256504 – Published 24 June, 2026

DOI: https://doi.org/10.1103/98j3-424f

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 microscopic mechanism for emergent fluctuating moments at the edge that could compromise the topological protection of helical edge states by time-reversal symmetry.

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Phys. Rev. Lett. 136, 256504– Published 24 June, 2026
  • Received 11 September 2025
  • Accepted 27 May 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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