Light can break symmetries in time and space. For example, circularly polarized light can break the time-reversal symmetry. This time-reversal symmetry breaking can be used to generate the light-induced magnetization.

Despite several studies on the light-induced symmetry breaking, whether light can break mirror symmetries remains unclear.

Recently, we have demonstrated that circularly or linearly polarized light can break the mirror symmetries. We considered monolayer graphene periodically driven by circularly or linearly polarized light, and studied the effects of the light field on the mirror symmetries and charge transport. We demonstrated that the symmetries of the xz and yz mirror planes of monolayer graphene can be broken by circularly or linearly polarized light. We also observed that the mirror symmetry breaking can be characterized by the off-diagonal charge conductivity, which is the transport coefficient describing the charge current perpendicular to the applied electric field. The conductivity becomes antisymmetric or symmetric with respect to its indices when circularly or linearly polarized light, respectively, is applied. This difference is due to the difference in time-reversal symmetry.

This study discovered the light-induced mirror symmetry breaking, paving the way for the optical control of mirror symmetries and the realization of various phenomena utilizing the mirror symmetry breaking. This also indicates that the origin of the light-induced anomalous Hall effect, which is described by the antisymmetric off-diagonal charge conductivity, is not simply the light-induced time-reversal symmetry breaking, but a combination of this and the light-induced mirror symmetry breaking.

(Written by N. Arakawa on behalf of all authors.)

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