Ultraviolet Magnetic Purcell Enhancement via Hybridized Anapole–Plasmon Modes in Al Metasurfaces

Enhancing light–matter interactions in the ultraviolet (UV) regime, particularly for magnetic dipole transitions, is pivotal for advancing quantum photonics and sensing technologies but remains challenging due to high material losses and difficulties in generating strong magnetic field confinement. This work proposes and numerically investigates a periodic metasurface composed of an Al nanodisk array separated from an Al film by an Al2O3 spacer. We demonstrate that by designing the lattice period, the magnetic anapole mode of individual nanodisk-gap-mirror units can be coherently coupled with propagating surface plasmon polaritons (PSPP) and electric toroidal dipoles (ETD) modes of the array. Tuning the period to 400 nm induces strong hybridization among these modes, yielding two hybridized resonances and significantly augmenting the magnetic local density of states near 400 nm. This synergistic coupling results in a pronounced magnetic Purcell factor of 16 at the UV wavelength of 400 nm. Our findings establish a promising material and structural platform for efficient magnetic light–matter interaction in the UV spectrum.