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  • Open Access

Tuning between a fractional topological insulator and competing phases at νT=2/3

Roger Brunner1, Titus Neupert2, and Glenn Wagner1,*

  • 1Institute for Theoretical Physics, ETH Zürich, 8093 Zürich, Switzerland
  • 2Department of Physics, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland

  • *Contact author: gwagner@phys.ethz.ch
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Phys. Rev. Research 8, 013159 – Published 11 February, 2026

DOI: https://doi.org/10.1103/3sdy-h5rq

Abstract

We study a spinful, time-reversal symmetric lowest Landau level model for a flatband quantum spin Hall system at total filling fraction νT=2/3. Such models are relevant, e.g., for spin-valley locked moiré transition metal dichalcogenides. The opposite Chern number of the two spins hinders the formation of a quantum Hall ferromagnet, instead favoring other phases. We study the phase diagram in dependence on different short-range Haldane pseudopotentials vm and uncover several phases: a fractional topological insulator, a phase-separated state, a spin-polarized fractional quantum Hall state, and the partially particle-hole transformed Halperin (111) state. The effect of the pseudopotentials vm depends on the parity of m, the relative angular momentum.

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Phys. Rev. Research 8, 013159– Published 11 February, 2026
  • Received 6 July 2025
  • Accepted 8 January 2026
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