Optical control of indirect exchange interaction through Floquet states

Abstract

Floquet states are photon-dressed electronic states that emerge when driven by a time-periodic optical excitation. The presence of these states changes the equilibrium picture of electronic transitions into one where transitions between Floquet states are allowed. We have recently investigated the indirect exchange (RKKY) interaction mediated by itinerant electrons that are driven strongly out of equilibrium by circularly polarized light in two-dimensional electron systems with parabolic and linear dispersion (graphene). Our results indicate that emergence of non-equilibrium Floquet states leads to new and qualitatively different regimes of RKKY coupling, in which the sign (ferromagnetic or antiferromagnetic) and the period of the RKKY oscillation become tunable through the frequency and amplitude of the laser. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Early Career Award #DE-SC0019326.