Revealing Quantitative Observation of Multi-Loop Super-Toroidal Currents in Plasmonic Meta-Atoms

TL;DR

This paper demonstrates the observation and control of multi-loop super-toroidal currents in plasmonic meta-atoms, revealing new ways to excite complex toroidal moments with high sensitivity for practical applications.

Contribution

It introduces a simple technique to monitor and switch between toroidal dipoles and super-toroidal moments in plasmonic meta-atoms, expanding understanding of complex electromagnetic excitations.

Findings

Identification of multi-loop super-toroidal spectral features

Ability to switch toroidal dipoles to super-toroidal moments by changing dielectric permittivity

Potential for high-sensitivity applications in plasmonic metamaterials

Abstract

Living in a world of resonances, there have been significant progresses in the field of excitation high-quality and multifunctional moments across a wide range of optical frequencies. Among all acknowledged resonances, the toroidal multipoles have received copious interest in recent years due to having inherent signatures in nature. As a fundamental member, toroidal dipole is a strongly localized electromagnetic excitation based on charge-current distributions, which can be squeezed in an extremely tiny spot. Although there have been extensive studies on the behavior and properties of toroidal dipoles to develop all-optical devices based on this technology, so far, all analyses are restricted to the first (1st) order toroidal dipoles. In this work, using a simple technique, we successfully monitored supporting exquisite multi-loop super-toroidal (MLST) spectral features in a planar multipixel plasmonic meta-atom. We quantitatively demonstrate that how a traditional toroidal dipole can be switched to a super-toroidal moment by varying the dielectric permittivity of the gaps between proximal pixels. This understanding paves new approaches for the excitation of complex multi-loop toroidal moments in plasmonic metamaterials with high sensitivity, applicable for various practical applications.