Hybridization of a magnon mode with a higher-order topological photonic corner state

Photonic corner states in higher-order topological lattices combine topological localization with zero-dimensional field confinement, making them promising interfaces for enhanced light–matter interactions. Yet their coupling to material excitations remains largely unexplored. Here, we demonstrate hybridization between the Kittel mode of a yttrium iron garnet sphere and a higher-order topological photonic corner state in a two-dimensional Su–Schrieffer–Heeger microwave lattice. Tuning the Kittel mode through the corner-state resonance produces a pronounced avoided crossing with a minimum frequency splitting of 155.44 MHz. Moving the same sphere to the adjacent site reduces the splitting to 36.22 MHz, whereas no splitting is resolved in the bulk. The resulting coupling-strength map is concentrated at the corners and corroborates the corner-state assignment relative to extended edge and bulk modes. Our results show that higher-order topological corner states can serve as localized interfaces for cavity magnonics and hybrid topological light–matter systems.