Robust spin splitting and fermiology in the layered altermagnet CoNb4Se8

Abstract

Altermagnetism defies conventional classifications of collinear magnetic phases, combining compensated magnetization with momentum-dependent, nonrelativistic spin splitting. While altermagnetic band splitting has been established in three-dimensional compounds such as MnTe and CrSb, layered altermagnets remain far less explored spectroscopically. Here, combining termination-resolved micro-ARPES, fine photon-energy mapping, spin-ARPES and density functional theory, we map the three-dimensional fermiology of the layered g-wave altermagnet CoNb${}_4$Se${}_8$, obtained by ordered Co intercalation of 2H-NbSe${}_2$. We resolve the spin-split branches of the altermagnetic pairs directly in the raw photoemission spectra and, with spin-ARPES at these experimentally identified momenta, show the reversal of the spin polarization at opposite momenta and between two regions of the sample, consistent with opposite time-reversal domains, and its absence along the symmetry-protected nodal $\Gamma$--K direction. We further report a weak low-temperature anomaly near $T_0\approx 50$ to 60 K, detected by magnetometry, temperature-dependent micro-ARPES and ultrafast reflectivity, whose microscopic origin remains open. These results provide a momentum-resolved benchmark of the electronic structure of a layered altermagnet.

Cited by in corpus (2)

• Relativistic Spin-momentum locking in altermagnets
• Altermagnetism, ARPES, symmetry, non-relativistic band splitting