Local Crystal Field Symmetry and d-Orbital Splitting of CoNb₄Se₈ Altermagnet from X-ray Spectroscopy

Altermagnets are a newly identified class of collinear antiferromagnets that exhibit spin-split electronic bands in the absence of net magnetization or spin-orbit coupling, owing to symmetry-enforced nonrelativistic spin splitting. CoNb₄Se₈ has emerged as a prototypical g-wave altermagnet, with recent spin-resolved photoemission and reflection spectroscopies directly confirming alternating spin textures above and below the Fermi level. While these signatures are now established in momentum space, a deeper understanding of their real-space origin—particularly the local d-orbital environment of the magnetic Co sites—remains incomplete.

Here, we present Co L-edge X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) measurements of CoNb₄Se₈ to probe the local electronic and crystal field environment of Co. By combining experimental spectra with multiplet calculations, we aim to clarify the symmetry and splitting of the Co d-orbitals and explore their connection to the underlying altermagnetic order. These results provide a complementary real-space perspective on a material that has become a model system for studying symmetry-driven spin splitting.