Symmetry-protected difference between spin Hall and anomalous Hall effects of a periodically driven multiorbital metal.

Nonequilibrium quantum states can be controlled via the driving field in periodically driven systems. Such control, which is called Floquet engineering, has opened various phenomena, such as the light-induced anomalous Hall effect. There are expected to be some essential differences between the anomalous Hall and spin Hall effects of periodically driven systems because of the difference in time-reversal symmetry. However, these differences remain unclear due to the lack of Floquet engineering of the spin Hall effect. Here we show that when the helicity of circularly polarized light is changed in a periodically driven t2g-orbital metal, the spin current generated by the spin Hall effect remains unchanged, whereas the charge current generated by the anomalous Hall effect is reversed. This difference is protected by the symmetry of a time reversal operation. Our results offer a way to distinguish the spin current and charge current via light and could be experimentally observed in pump-probe measurements of periodically driven Sr2RuO4. Non-equilibrium states can be induced in a given system using periodic driving and the underlying physics understood using Floquet theory. Here, the authors model a periodically driven t2g-orbital metal and demonstrate how the spin Hall and anomalous Hall effects are realized and can be distinguished by their response to circularly polarized light with different helicities. [ABSTRACT FROM AUTHOR]