  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.

Strongly Correlated Electrons