Excitons in NiPS₃—A Computational and Experimental Study

In recent years, the study of NiPS₃ and other members of the transition metal phosphorus trichalcogenide class of materials (MPX₃) has accelerated significantly. As a class of antiferromagnetic van der waals materials, they provide a unique platform to study magnetism and spin-related phenomena in the 2-D limit. In particular, in NiPS3 an exciton with remarkably thin linewidth was recently observed in the photoluminescence and absorption, and moreover the appearance of this exciton seems to be correlated with the magnetic ordering of the material. While there have been a variety of papers on this exciton since its initial observation, there is still no consensus as to its origin, and it is thus unclear how one might utilize this exciton in novel technologies or to study novel physics.<br/>Here I will present my work on studying this exciton, and generally NiPS3, both computationally and experimentally. I will present my experimental results verifying and characterizing the exciton through temperature-dependent photoluminescence and reflectance measurements. I will also discuss my computational results, mainly utilizing density functional theory (DFT) and the bethe salpeter equation (BSE), highlighting the effects of certain approximations such as the inclusion of a hubbard U parameter (or lack thereof). My experimental results are in close agreement with previous observations of the exciton, and I find encouraging overlap between experiment and my BSE results, mainly in the predicted absorption curves and exciton radiative lifetime.