Direction-dependent coherent-dissipative indirect coupling in cavity magnonics

We demonstrate direction-dependent coherent-dissipative indirect coupling in cavity magnonics. A photon-like self-cavity resonance of a yttrium iron garnet disk first hybridizes with the ferromagnetic resonance to form magnon–photon polaritons. The lower polariton subsequently interacts with the effective cavity response near an interference induced antiresonance formed by adjacent resonances of a two port quadrant-stadium cavity. Under otherwise identical experimental conditions, the same hybridization exhibits level repulsion in forward transmission S21 and level-attraction-like behavior in backward transmission S12, corresponding to coherent-dominated and dissipative-dominated responses, respectively. Independent phase measurements yield distinct directional phase responses, which are directly used as the phase parameters in a hierarchical input-output model. The model captures the principal direction-dependent hybridization features and relates the reversal of the coupling character to the effective phase structure of the polariton cavity port scattering pathway. The resulting nonreciprocity produces compound isolation in opposite directions within two distinct and nonoverlapping frequency windows, providing a route toward multiband nonreciprocal signal processing.