Hybrid Superscattering Driven by Toroidal Dipole

TL;DR

This paper demonstrates that the toroidal dipole can actively enhance electromagnetic scattering, leading to superscattering effects that surpass fundamental limits, with potential applications in advanced photonic devices.

Contribution

It introduces a new hybrid superscattering paradigm driven by the toroidal dipole, combining multiple mechanisms to achieve significantly enhanced light scattering.

Findings

Normalized scattering cross-section exceeds dipole limit due to toroidal dipole-magnetic quadrupole interplay.

Hybrid mechanisms synergistically enhance superscattering beyond single-channel limits.

Experimental GHz measurements confirm theoretical predictions of toroidal superscattering.

Abstract

The dynamic toroidal dipole is a unique radiation source beyond standard multipoles. Since its first demonstration 15 years ago, it has attracted growing theoretical and experimental interest. Research mainly aims to enhance its weak electromagnetic coupling to free space. Here we report on a surprising finding that the toroidal dipole can, in fact, be engaged in the enhancement of electromagnetic scattering per se driving the so-called superscattering the regime of anomalously strong light scattering where the total cross-section of the effect exceeds the fundamental single-channel limit. We introduce a new paradigm of hybrid superscattering enabled by the toroidal dipole, which we implement with a dielectric scatterer of a simple geometry, and demonstrate for the first time that two complementary mechanisms of superscattering the Friedrich-Wintgen mechanism and resonance overlap can act synergistically to yield the substantially enhanced effect. Using coupled-dipole theory, full-wave numerical modeling and coupled-mode theory, we identify and quantify the dominant multipolar contributions and show that the normalized scattering cross-section exceeds the dipole limit due to a toroidal dipole-magnetic quadrupole interplay. These findings are supported by experimental measurements in the GHz frequency range using a dimer of ceramic cubes, which confirm both the spectral and spatial features of toroidal superscattering. Our results open a new powerful route to engineering strong light-matter interaction via peculiar toroidal modes (never observed before) with potential applications in toroidal superscattering metamaterials and metasurfaces, photonic devices, and sensors.