Discovery of van Hove singularities: electronic fingerprints of 3Q magnetic order in a van der Waals quantum magnet.
basic_science · Level V
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- Record sourced from PubMed, PMID 41794798.
- Also identified by DOI 10.1038/s41467-026-70063-5 and PMC identifier 13096175.
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Abstract
Magnetically intercalated transition metal dichalcogenides are emerging as a rich platform for exploring exotic quantum states in van der Waals magnets. Among them, Co<sub>x</sub>TaS<sub>2</sub> 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- <math xmlns="http://www.w3.org/1998/Math/MathML"> <msup><mrow><mi>K</mi></mrow> <mrow><mo>'</mo></mrow> </msup> </math> 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.