Abstract
Magnetically intercalated transition metal dichalcogenides are emerging as a rich platform for exploring exotic quantum states in van der Waals magnets. Among them, CoxTaS2 has attracted intense interest following the recent discovery of a distinctive 3Q magnetic ground state and a pronounced topological Hall effect below a critical doping of x ≈ 1/3, both intimately tied to cobalt concentration. To date, direct signatures of this enigmatic 3Q magnetic order in the electronic structure remain elusive. Here we report a comprehensive doping dependent angle resolved photoemission spectroscopy study that unveils these long-sought fingerprints. Our data reveal an unexpected inverse-Mexican-hat dispersion along the K-M-\({\mathrm{K}}^{\prime}\) direction, accompanied by two van Hove singularities. These features are consistent with theoretical predictions for a 3Q magnetic order near three-quarters band filling on a cobalt triangular lattice. These results provide evidence of 3Q magnetic order in the electronic structure, establishing TMD van der Waals magnets as tunable materials to explore the interplay between magnetism and topology.
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Data availability
The ARPES data generated during this study have been deposited in the Zenodo database under accession code: https://doi.org/10.5281/zenodo.18285547.
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Acknowledgements
We thank Sang-Wook Cheong for insightful discussions. We thank Cheng Hu for taking the data for 2H-TaS2. This work was primarily supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under contract No. DE-AC02-05-CH11231 (Quantum Materials Program KC2202). This research used resources of the Advanced Light Source, a US DOE Office of Science User Facility under Contract No. DE-AC02-05CH11231. G.C. and D.D. acknowledge support from the National Research Foundation, Singapore, under its Fellowship Award (NRFNRFF13-2021-0010) and from the Singapore Ministry of Education (MOE) Academic Research Fund Tier 3 grant (MOEMOET32023-0003).
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A.L. and H.-L.L. conceived this project. H.-L.L. performed the ARPES experiments with assistance from M.H., H.J., L.M., A.F., C.J., and A.B. and analyzed the resulting data. J.R., C.X., and J.A. contributed to crystal synthesis. D.D. and G.C. contributed to DFT calculations. D.-H.L. contributed to theoretical work. H.-L.L., D.-H.L., and A.L. wrote this paper. All authors participated in discussions and provided comments on the paper.
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Luo, HL., Rodriguez, J., Dutta, D. et al. Discovery of van Hove singularities: electronic fingerprints of 3Q magnetic order in a van der Waals quantum magnet. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70063-5
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DOI: https://doi.org/10.1038/s41467-026-70063-5
