The high-order toroidal moments and anapole states in all-dielectric photonics

TL;DR

This paper explores high-order toroidal moments and anapole states in all-dielectric nanophotonics, revealing new nonradiating states and near-field configurations that advance understanding and control of light at the nanoscale.

Contribution

It introduces detailed analysis of high-order toroidal moments using Cartesian multipole decomposition, including electric octupole toroidal moments, and demonstrates high-order nonradiating anapole states.

Findings

High-order toroidal moments up to electric octupole identified.

Nonradiating anapole states with intense near-fields demonstrated.

Cartesian multipole analysis provides physical insight into vortex-like current distributions.

Abstract

All-dielectric nanophotonics attracts ever increasing attention nowadays due to the possibility to control and configure light scattering on high-index semiconductor nanoparticles. It opens a room of opportunities for the designing novel types of nanoscale elements and devices, and paves a way to advanced technologies of light energy manipulation. One of the exciting and promising prospects is associated with the utilizing so called toroidal moment being the result of poloidal currents excitation, and anapole states corresponding to the interference of dipole and toroidal electric moments. Here, we present and investigate in details via the direct Cartesian multipole decomposition higher order toroidal moments of both types (up to the electric octupole toroidal moment) allowing to obtain new near- and far-field configurations. Poloidal currents can be associated with vortex-like distributions of the displacement currents inside nanoparticles revealing the physical meaning of the high-order toroidal moments and the convenience of the Cartesian multipoles as an auxiliary tool for analysis. We demonstrate high-order nonradiating anapole states (vanishing contribution to the far-field zone) accompanied by the excitation of intense near-fields. We believe our results to be of high importance for both fundamental understanding of light scattering by high-index particles, and a variety of nanophotonics applications and light governing on nanoscale.