Coherent coupling between YBCO superconducting resonators and sub-micrometer-thick YIG films

In cavity magnonics, magnon–photon hybridization has been widely investigated for both fundamental studies and applications. Planar superconducting resonators operating at microwave frequencies have demonstrated the possibility to achieve high couplings with magnons by exploiting the confinement of the microwave field in a reduced volume. Here we report a study of the coupling of high-Tc YBCO superconducting waveguides with 104-nm-thick YIG magnetic films. We study the evolution of mode frequencies as a function of temperature and extract the coupling strength of hybrid magnon–photon modes. We show that the experimental results can be reproduced using a simple model in which the temperature dependence of the penetration depth accounts for the evolution of the polaritonic spectrum.