Nonlinear Magnon Polaritons
Oscar Lee, Kei Yamamoto, Maki Umeda, Christoph W. Zollitsch, Mehrdad Elyasi, Takashi Kikkawa, Eiji Saitoh, G. Bauer, H. Kurebayashi
Abstract
We experimentally and theoretically demonstrate that nonlinear spin-wave interactions suppress the hybrid magnon-photon quasiparticle or "magnon polariton" in microwave spectra of a yttrium iron garnet film detected by an on-chip split-ring resonator. We observe a strong coupling between the Kittel and microwave cavity modes in terms of an avoided crossing as a function of magnetic fields at low microwave input powers, but a complete closing of the gap at high powers. The experimental results are well explained by a theoretical model including the three-magnon decay of the Kittel magnon into spin waves. The gap closure originates from the saturation of the ferromagnetic resonance above the Suhl instability threshold by a coherent backreaction from the spin waves.