Magnetic Radiative Purcell Enhancement by Magnetic anapole in the gap of nanodisk on metal mirror structure

Magnetic anapole (MA) states are potential research hotspots in the fields of sensing, information, and photonics owing to their substantial field enhancement capabilities. In this work, we systematically investigated the MA states formed in the gap of the nanodisk on metal mirror (NDOM) structure, composed of a gold nanodisk and gold mirror. The corresponding magnetic near field exhibits a characteristic anapole-like magnetic hotspot distribution, and a high magnetic enhancement factor of up to 40 is observed. Through multipolar expansion analysis, we also revealed that the interference cancellation between the magnetic dipoles and the magnetic toroidal dipoles leads to the MA state in the gap. Furthermore, by introducing a magnetic dipole into the gap, we observed a significant radiative magnetic Purcell factor, reaching up to approximately 76, which follows the MA state peak in the scattering spectrum at 802 nm. Notably, as the gap size decreases and the radius of the nanodisk increases, the wavelength at which the radiative magnetic Purcell factor attains its maximum value shifts towards longer wavelengths. Additionally, increasing the thickness of the gold nanodisk leads to an enhancement in the radiative magnetic Purcell factor, which stabilizes after reaching a thickness of about 50 nm. This structure facilitates research on the interaction between light and matter.