Non-Equilibrium Theory of Orbital Magnetization in Periodically Driven Solids

Berry phases play an important role in the orbital magnetization of crystals with broken time reversal symmetry. Although the theory of orbital magnetization was now well established in equilibrium with extension to interacting systems, the influence of optical driving field on the orbital magnetization is largely unexplored. In this work, we have developed a theory of orbital magnetization in a periodically driven solid by a strong optical field. Using the Keldysh-Floquet Green’s function formalism, we find the non-perturbative photon-induced corrections to the time-averaged orbital magnetization. Our theory highlights the combined influence of Berry phases and multiphoton processes on the magnetization.