Long-range magnetic ordering coupling with bulk excitonic effect and defect related sharp peak in van der Waals antiferromagnet NiPS₃

The antiferromagnetic van der Waals material NiPS₃ has recently emerged as a novel system for its versatile long-range magnetic ordering and its strong correlation with electronic and optical properties. We first studied the quasiparticle and optical properties of pristine NiPS₃, and revealed the mechanism of the coupling between excitonic effect and magnetic ordering from first-principles many-body perturbation theory. We found the experimental sharp peak below the main absorption edge around 1.48 eV cannot be explained by the excitonic excitation from bulk states. Then we studied the optoelectronic properties of S vacancy defect states in different magnetic ordering phases. We also studied the photoluminescence lineshape, and exciton lifetime through radiative and nonradiative decay, and emitted photon polarization of the defect related sharp peak. We found that the defect state induces disparate transitions and photon polarization while varying long-range magnetic ordering. Our results and proposed mechanisms are in good agreement with recent experiment data. We propose that the appearance of this sharp peak below the band gap could be a unique probe for the magnetic ordering of this system.