Tunable interaction between excitons and hybridized magnons in a layered semiconductor

The interaction between distinct excitations in solids is of both fundamental interest and technological importance. One such interaction is the coupling between an exciton, a Coulomb bound electron–hole pair, and a magnon, a collective spin excitation. The recent emergence of van der Waals magnetic semiconductors1 provides a platform to explore these exciton–magnon interactions and their fundamental properties, such as strong correlation2, as well as their photospintronic and quantum transduction3 applications. Here we demonstrate the precise control of coherent exciton–magnon interactions in the layered magnetic semiconductor CrSBr. We varied the direction of an applied magnetic field relative to the crystal axes, and thus the rotational symmetry of the magnetic system4. Thereby, we tuned not only the exciton coupling to the bright magnon, but also to an optically dark mode via magnon–magnon hybridization. We further modulated the exciton–magnon coupling and the associated magnon dispersion curves through the application of uniaxial strain. At a critical strain, a dispersionless dark magnon band emerged. Our results demonstrate an unprecedented level of control of the opto–mechanical–magnonic coupling, and a step towards the predictable and controllable implementation of hybrid quantum magnonics5–11. The interaction between distinct excitations in solids is of both fundamental interest and technological importance. The layered magnetic semiconductor CrSBr exhibits strong coupling between excitons and coherently hybridized magnons, where both magnetic fields and strain can tune the coupling precisely.