Do magnons play a role in excitonic nonlinearity of van der Waals magnets?

Excitons are quasiparticles that can significantly alter the optical properties of semiconductors. Interacting excitons can lead to large optical nonlinearity and various emergent phases of matter. These interactions are commonly driven by exchange interactions or phase space filling. Here, we study previously unexplored mechanisms for excitonic interactions possible in correlated materials with excitons coupled to other degrees of freedom. Specifically, we demonstrate that in CrSBr, an antiferromagnetic semiconductor, magnons mediate excitonic interactions, leading to pronounced optical nonlinearity. Magnons and excitons typically remain independent due to their differing energy scales. However, our study reveals an exciton-density-dependent energy shift facilitated by a magnonic adjustment of the spin canting angle. Our theoretical model accurately captures how the strong exciton-magnon coupling leads to magnon-mediated exciton interactions. Additionally, we identify distinct nonlinear responses between the two types of excitons, A and B, in CrSBr, which stem from their different magneto-optical characteristics. This work highlights the emergence of quasiparticle-mediated interactions in correlated quantum materials, leading to large nonlinear optical responses and enabling novel device concepts, such as magnon-mediated quantum transducers.



Funding: Gordon and Betty Moore Foundation (Grant No. 12764), Army Research Office (W911NF-23-1-0394), and NSF (2216838).