Toroidal dipole induced transparency for core-shell nanoparticles

TL;DR

This paper explores how toroidal dipoles influence the scattering and transparency of core-shell nanoparticles, revealing new mechanisms for controlling optical properties in nanostructures.

Contribution

It introduces a Cartesian multipole expansion method including toroidal multipoles to analyze nanoparticle scattering, identifying non-trivial transparency mechanisms caused by toroidal-electric interference.

Findings

Toroidal dipoles can be excited in high-permittivity dielectric nanoparticles.

Two types of scattering transparency are classified: trivial and non-trivial.

Toroidal moments significantly affect nanoparticle scattering in optical regimes.

Abstract

We investigate the scattering properties of spherical nanoparticles by employing a Cartesian multipole expansion method which has incorporated radiating toroidal multipoles. It is shown that toroidal dipoles, which are negligible under long-wavelength approximations, can be excited within high-permittivity dielectric nanoparticles and significantly influence the scattering profile in the optical regime. We further reveal that the scattering transparencies of core-shell plasmonic nanoparticles can be classified into two categories: i) the trivial transparency with no effective multipole excitations within the particle, and ii) the non-trivial one induced by the destructive interferences of induced electric and toroidal multipoles. The incorporation of toroidal moments offers new insights into the study into nanoparticle scattering in both the near- and far-fields, which may shed new light to many related applications, such as biosensing, nanoantennas, photovoltaic devices and so on.