Classify the microscopic nature of excitons in NiPS3

Determine whether the excitons observed in the antiferromagnetic van der Waals material NiPS3 are Hund excitons, ligand-to-metal charge-transfer excitons arising from S 3p to Ni 3d transitions, or coherent many-body excitons, and provide a definitive classification grounded in direct spectroscopic or dynamical evidence.

Background

NiPS3 hosts sharp excitonic features and strong coupling to the spin background, but multiple interpretations of the exciton type have been proposed in the literature, including Hund excitons, ligand-to-metal charge-transfer excitons, and coherent many-body excitons. The authors note that despite significant recent progress, a consensus on the microscopic identity of these excitons has not been reached.

Clarifying the exciton type is important for understanding the coupling mechanisms to magnetic order and for interpreting ultrafast dynamics, as different exciton classes imply distinct formation, relaxation, and interaction pathways with spin and lattice degrees of freedom.