Electronic structure of a layered altermagnetic compound CoNb₄Se₈

Altermagnets (AMs) have recently emerged as a promising class of magnetic materials characterized by unique spin-splitting even in the absence of both net magnetic moments and spin-orbit coupling. Despite numerous theoretical predictions, experimental evidence of such spin-splitting in real materials remains limited. In this study, we use angle-resolved photoemission spectroscopy (ARPES) combined with density functional theory (DFT) calculations to investigate the electronic band structure of the altermagnet candidate CoNb₄Se₈. This material features an ordered sublattice of intercalated Co atoms within NbSe₂ layers. Magnetization and electrical resistivity measurements reveal the onset of antiferromagnetism below 168 K. Temperature-dependent ARPES data, supported by DFT calculations, uncover spin-split bands along the M–Γ–M high-symmetry direction. The observation of spin-splitting in this high-temperature altermagnet opens new avenues for exploring its electronic properties and potential applications in spintronic technologies.