Optical methods and in particular ultrafast pump-probe spectroscopy are powerful tools to probe the dynamics of collective excitations.

Inspired by recent experiments, we have sought out to uncover microscopic mechanisms that allow for the generation of magnons in antiferromagnets via ultrafast optical light pulses that lie within the material's optical gap:

In the case of the transition metal oxide Sr2IrO4 [1,2], we were able to show that there exists symmetry-allowed coupling between pairs of magnons and the electric field of the driving light. Integrating out high-energy two-magnon excitations yields an effective coupling between electric field bilinears and a low-energy magnon, the dynamics of which can be observed via a subsequent probe beam [2].

For the van der Waals antiferromagnet NiPS3 [3], two separate magnon generation mechanisms are at play, depending on the driving light's frequency: if the system is driven near an orbital dd-resonance, the light generates an effective single-ion anisotropy which takes the system out of equilibrium. At lower energies, we suggest that a light-induced modification of the exchange couplings launches a higher-energy magnon mode.

In an recent collaboration with the group of N. Gedik (MIT), we have modelled the excitation of magnons by pumping an orbital resonance in NiPS3, accounting for the non-equilibrium dynamics involving decoherence and dissipation within a Lindblad master equation framework [4].