Coupling microwave photons to topological spin textures in Cu2OSeO3

Topologically protected nanoscale spin textures, known as magnetic skyrmions, possess particlelike properties and feature emergent magnetism effects. In bulk cubic helimagnets, distinct skyrmion resonant modes are already identified using a technique such as ferromagnetic resonance in spintronics. However, direct light-matter coupling between microwave photons and skyrmion resonance modes still needs to be demonstrated. Utilizing two distinct cavity systems, we observe a direct interaction between the cavity resonant mode and two resonant skyrmion modes, the counterclockwise gyration and breathing modes, in bulk Cu2OSeO3. For both resonant modes, we find the largest coupling strength at 57 K indicated by an enhancement of the cavity linewidth at the degeneracy point. We study the effective coupling strength as a function of temperature within the expected skyrmion phase. We attribute the maximum in effective coupling strength to the presence of a large number of skyrmions, and correspondingly to a completely stable skyrmion lattice. Our experimental findings indicate that the coupling between photons and resonant modes of magnetic skyrmions depends on the relative density of these topological particles instead of the pure spin number in the system.