Boosting magnetic field enhancement with radiative couplings of magnetic modes in dielectric nanostructures.

Abstract

Dielectric nanostructures can readily support considerable magnetic field enhancements that offer great potential applications in field enhanced spectroscopies. However, the magnetic fields of dielectric structures are usually distributed within the entire volume, which brings challenge to the further increment of the magnetic field enhancement. Here, we theoretically demonstrate that the magnetic field enhancement in dielectric nanostructures can be boosted through the radiative couplings of magnetic modes. Our concentric structure consists of a hollow disk and a ring. The disk has a magnetic dipole mode. The ring has two magnetic dipole modes that are out of phase. Strong radiative interactions between the modes on the disk and the ring can occur, which result in a net constructive coupling effect. For a lossless material with n = 3.3, a sharp peak can be obtained on the scattering spectrum of the coupled system due to the radiative interactions. The corresponding resonant magnetic field enhancement at the disk center reaches 96 times. This enhancement is about 7 times higher than that of an individual disk. The structure with a lossy material Si is also considered, where radiative couplings and boosted magnetic field can also be obtained. Our research reveals the strong radiative mode couplings in dielectric structures and is important for furthering our understanding on the light-matter interactions at the nanoscale.