Exciton-spin interaction in charge-transfer insulators

We theoretically investigate the correlation between magnetism and exciton creation in antiferromagnets such as van der Waals material NiPS₃ by deriving an effective model for exciton-spin interactions in charge-transfer insulators. We show that in these systems the spin exchange interaction around the exciton is strongly enhanced from the original interaction. The exciton behaves like the impurity in the antiferromagnetic background and the local spins related to the exciton site prefer to make the spin multiplet because of the strong spin interaction. We also consider the mobility of the exciton and discuss possible optically allowed excitation peaks associated with the exciton creation and modified spin structure.