Double anticrossings induced by nonlinear magnon interactions

We observe pump-induced double anticrossings whose gap sizes and center-frequency shifts depend strongly on pump power, indicating a nonlinear mechanism. The anticrossings vanish at high magnetic fields, where energy conservation suppresses three-magnon splitting, thereby identifying the underlying process as three-magnon scattering. We attribute the double anticrossings to nondegenerate three-magnon splitting, which generates two magnon populations at distinct frequencies. Each population forms a standing-wave mode and couples independently to the Kittel mode, giving rise to two effective coupling channels. These results demonstrate that nonlinear magnon interactions can dynamically generate multiple coupling channels within a single system.