Speaker
Description
Periodically driven magnetic systems provide a versatile platform for controlling collective spin excitations far from equilibrium. We theoretically study a two-dimensional antiferromagnet driven by in-plane polarized light, where the exchange interactions acquire Floquet modulations. The drive induces short-time amplification of selected magnon modes, which can be effectively described by a non-Hermitian magnon Hamiltonian. At longer times, nonlinear magnon interactions regulate the instability and lead to large-amplitude coherent oscillations. Our work identifies a mechanism by which a spatially local Floquet modulation of exchange interactions functions as a mode-selective magnon source. We further analyze the quantum geometry of the associated non-Hermitian magnon bands and discuss its implications for driven spin dynamics.