Exciton dressing by extreme nonlinear magnons in a layered semiconductor

Recent progress in van der Waals magnetic semiconductors has allowed for novel physics to emerge from the interplay of spin and charge, which we leverage here to we demonstrate nonlinear optomagnonic coupling. In the layered antiferromagnetic semiconductor CrSBr, we employ time resolved spectroscopy and observe exciton states coupled to up to 20 magnon harmonics resulting from extreme magnon nonlinearities. We also create tunable optical sidebands via sum- and difference-frequency generation between two optically bright magnon modes under symmetry-breaking magnetic fields. Moreover, we can tune the observed difference-frequency generation mode into resonance with one of the fundamental magnons, which results in parametric magnon amplification. Our findings realize the modulation of optical-frequency excitons with nonlinear magnons at microwave frequencies, which could find applications in magnonics and hybrid quantum systems, and provide a method for optomagnonic neuromorphic computing devices.