Ultra Strong Magnon-Photon Coupling Achieved by Magnetic Films in Contact with Superconducting Resonators

Coherent coupling of magnon excitations and microwave photons in a cavity may disclose new paths to unconventional phenomena and for novel applications. Here, we show that large couplings and cooperativities can be achieved with YIG (Yttrium Iron Garnet) films in contact with coplanar resonators made of superconducting YBCO. Transmission spectra, which are analysed by a modified Hopfield model, show that the coupling of the dominant magnetic mode with photons exceeds 0.2 times the cavity frequency, thus demonstrating the achievement of the ultra strong coupling regime with this architecture.