Magnetic Order in Laser-Irradiated Kagome Antiferromagnets

Dispersionless "zero energy mode'' is one of the hallmarks of frustrated kagome antiferromagnets (KAFMs). It points to extensive classically degenerate ground-states. The "zero energy mode'' can be observed experimentally when lifted to a flat mode at finite energy by a strong intrinsic magnetic anisotropy. In this letter, we study the effects of irradiation of laser light on the KAFMs. We adopt the magnon picture without loss of generality. It is shown that circularly or linearly polarized light lifts the "zero energy mode'', stabilizes magnetic order, and induces energy gaps in the KAFMs. We find that the circularly polarized light-induced anisotropies have similar features as the intrinsic in-plane and out-of-plane Dzyaloshinskii-Moriya interaction in KAFMs. The former stabilizes long-range magnetic order and the latter induces spin canting out-of-plane with nonzero scalar spin chirality. The Floquet thermal Hall effect shows that the synthetic magnetic excitation modes in the case of circularly polarized light are topological, whereas those of linearly polarized light are not.