Light-Driven Exchange Interaction between Strong Magnetic Impurities in Irradiated Graphene*

Strong impurity scattering can induce resonance features in the interaction between magnetic impurities in graphene. Circularly polarized light can further open a band gap at the Dirac points allowing for in-gap impurity states. We present our results for the indirect exchange interaction between magnetic impurities in graphene driven by off-resonant circularly polarized light. Using the Floquet T-matrix formalism, our analysis captures the non-perturbative effects of both spin exchange coupling and potential scattering resulting from strong magnetic impurities. We obtain the local density of states and show that increasing light field brings the impurity levels closer to the Dirac point. When impurity spins are located at the same sublattices (AA), the exchange interaction changes from antiferromagnetic to ferromagnetic values with increasing distance. We further find that irradiation extends the range of this antiferromagnetic exchange to larger distances. For impurity spins located at different sublattices (AB), a light-tunable impurity resonance appears, driving the exchange to antiferromagnetic values over shorter distances. Our findings demonstrate that in-gap impurity states play a central role in understanding light-driven indirect exchange interaction.