Optical Hall conductivity of a Floquet topological insulator

Results are presented for the optical Hall conductivity of a Floquet topological insulator (FTI) for an ideal closed quantum system, as well as an open system in a nonequilibrium steady state with a reservoir. The steady state, even for the open system, is strongly dependent on the topological phase of the FTI, with certain phases showing a remarkable near cancellation from pockets of Berry curvature of opposite signs, leading to a suppressed low-frequency Hall conductivity that also shows an anomalous temperature dependence by increasing as the temperature of the reservoir is increased. Such a behavior is in complete contrast to heating and arises because of a strong modification of the effective system-reservoir coupling by the laser. The Berry curvature of the Floquet modes is time dependent, and its frequency components are found to control the main features of the high-frequency Hall conductivity.