Discovery of Van Hove Singularities: Electronic Fingerprints of 3Q Magnetic Order in a van der Waals Quantum Magnet

TL;DR

This study uses angle resolved photoemission spectroscopy to identify electronic signatures of 3Q magnetic order in CoxTaS2, revealing van Hove singularities and an inverse Mexican hat dispersion linked to magnetic topology.

Contribution

It provides the first direct electronic structure evidence of 3Q magnetic order in CoxTaS2, connecting experimental data with theoretical predictions.

Findings

Identification of van Hove singularities in CoxTaS2

Observation of an inverse Mexican hat dispersion

Evidence linking electronic structure to 3Q magnetic order

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-K 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.