Direct probing of strong magnon-photon coupling in a planar geometry

We demonstrate direct probing of strong magnon-photon coupling using Brillouin light scattering spectroscopy in a planar geometry. Miniaturized, planar device design is imperative for the potential integration of magnonic hybrid systems in future coherent information technologies. The magnonic hybrid system comprises a split-ring resonator loaded with epitaxial yttrium iron garnet thin films of 200 nm and 2.46 µm thickness. The Brillouin light scattering (BLS) measurements are combined with microwave spectroscopy measurements where both biasing magnetic field and microwave excitation frequency are varied. The cooperativity for the 200 nm-thick YIG films is found to be 1.1, and larger cooperativity of 29.1 is found for the 2.46 µm-thick YIG film. We reveal that BLS is advantageous for probing the magnonic character of magnon-photon polaritons, while microwave absorption is more sensitive to the photonic nature. Furthermore, successfully detecting the magnonic hybrid excitation by BLS is an essential step for the up conversion of quantum signals from the optical to the microwave regime in hybrid quantum systems.