Design of hybrid anapole metal–dielectric cavities for giant magnetic Purcell enhancement

Magnetic-field enhancement in photonic nanostructures is fundamentally limited by the weak magnetic response of natural materials and the lack of general design principles for simultaneously controlling electric and magnetic resonances. Here, we propose a design methodology for metal–dielectric cavities based on mode hybridization and radiation-loss engineering. Using a symmetric Au–Si–Au cavity as a model system, we demonstrate that coupling a metal–insulator–metal cavity resonance with a dielectric electric anapole mode generates a hybrid magnetic anapole featuring spatially co-localized electric and magnetic energy confinement. Systematic structural analysis establishes that the magnetic-field enhancement is primarily determined by the hybridization strength between the cavity and anapole modes, whereas the resonance quality factor is governed by radiative loss. Guided by these structure–performance relationships, lattice-assisted collective coupling suppresses radiation leakage, increasing the quality factor from 24 to 148 and enhancing the electric and magnetic fields from 17 and 35 to 50 and 120, respectively. Consequently, the magnetic Purcell factor reaches ∼ 1200, representing a 3–5-fold improvement over conventional magnetic-resonance designs. This work establishes transferable design principles for engineering high quality factor metal–dielectric photonic materials with enhanced magnetic light–matter interactions.