Exchange Interaction Between Magnetic Adatoms in Irradiated Graphene

We present a theory for the non-equilibrium RKKY interaction in graphene irradiated by circularly polarized light. A k.p theory of the graphene Floquet Hamiltonian is developed, which provides a successive approximation scheme as the light-matter coupling strength is increased. Based on the Floquet k.p Hamiltonian, we calculate the real-space Floquet Green’s functions and the time-averaged RKKY interaction using Floquet-Keldysh formalism. We find that optical illumination generally suppresses the exchange interaction in undoped graphene, due to a band gap opened at the Dirac point. Results for doped graphene will also be presented.