Probing the Band Structure of the Strongly Correlated Antiferromagnet NiPS₃ across Its Phase Transition

NiPS₃ is an exfoliable van der Waals intralayer antiferromagnet with a zigzag-type spin arrangement. It is distinct from other TMPS₃ (TM: transition metal) materials by optical excitations into a strongly correlated state that is tied to the magnetic properties. However, the related fundamental band structure across the antiferromagnetic phase transition has not been probed yet. Here, we use angular-resolved photoelectron spectroscopy with μm resolution in combination with DFT + U calculations for that purpose. We identify a characteristic band shift across the T_N. It is attributed to bands of mixed Ni and S character related to the superexchange interaction of the Ni 3t_2g orbitals. Moreover, we find a structure above the valence band maximum with little angular dispersion that could not be reproduced by the calculations. The discrepancy suggests the influence of many-body interactions beyond the DFT + U approximations, in striking contrast to the results on MnPS₃ and FePS₃, where these calculations were sufficient for an adequate description.