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Probing Quantum Anomalous Hall States in Twisted Bilayer WSe2 via Attractive Polaron Spectroscopy

Beini Gao1, Mahdi Ghafariasl1,*, Mahmoud Jalali Mehrabad1,*, Tsung-Sheng Huang1,*, Lifu Zhang2, Deric Session1, Pranshoo Upadhyay1, Rundong Ma3, Ghadah Alshalan1 et al.

Daniel Suarez1, Supratik Sarkar1, Suji Park4, Houk Jang4, Kenji Watanabe5, Takashi Taniguchi5, Ming Xie6,7, You Zhou2,†, and Mohammad Hafezi1,‡

  • *These authors contributed equally to this work.
  • †Contact author: youzhou@umd.edu
  • ‡Contact author: hafezi@umd.edu
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Phys. Rev. X 16, 021037 – Published 18 May, 2026

DOI: https://doi.org/10.1103/259w-bpxx

Abstract

Moiré superlattices in semiconductors exhibit a rich variety of interaction-induced topological states, including quantum anomalous Hall (QAH) effects [1–8]. A recent study hinted that twisted WSe2 homobilayer (tWSe2) could host a QAH state but lacked direct evidence of ferromagnetism, a key hallmark of this phase [9]. Here, we report the first direct evidence of QAH states in tWSe2 with spontaneous ferromagnetism. Specifically, we employ polarization-resolved attractive polaron spectroscopy on a dual-gated, 2° tWSe2 and observe direct signatures of spontaneous time-reversal symmetry breaking at hole filling ν=1. Together with a Chern number (C) measurement via Streda formula analysis, we identify this magnetized state as a topological state, characterized by C=1. Furthermore, we demonstrate that these topological and magnetic properties are tunable via a finite displacement field, between a QAH ferromagnetic state and an antiferromagnetic state. Our findings position tWSe2 as a highly versatile, stable, and optically addressable platform for investigating topological order and strong correlations in two-dimensional landscapes.

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Directly observing the quantum anomalous Hall effect in twisted WSe2 has remained a challenge despite the material’s potential to host topological states that carry electric current along their edges without resistance. We addressed this by using magneto-optical spectroscopy to probe a twisted bilayer of WSe2 at temperatures near absolute zero. By monitoring the behavior of attractive polarons, we detected spontaneous magnetism and confirmed the existence of a topological phase with a Chern index of one at specific electron fillings. We also found that the magnetic order can be reversibly switched between ferromagnetic and antiferromagnetic states through the application of a perpendicular electric field. These results establish twisted WSe2 as a highly tunable and stable platform for engineering topological quantum phases. Our work provides a framework for utilizing optical signatures to identify and manipulate exotic electronic states in moiré semiconductors.

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Phys. Rev. X 16, 021037– Published 18 May, 2026
  • Received 4 August 2025
  • Revised 16 December 2025
  • Accepted 31 March 2026
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