Resonant Transparency and Non-Trivial Non-Radiating Excitations in Toroidal Metamaterials

V A Fedotov,A V Rogacheva,V Savinov,N I Zheludev,D P Tsai

doi:10.1038/srep02967

V A Fedotov, A V Rogacheva + Show 3 more

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https://doi.org/10.1038/srep02967

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Abstract

Engaging strongly resonant interactions allows dramatic enhancement of functionalities of many electromagnetic devices. However, resonances can be dampened by Joule and radiation losses. While in many cases Joule losses may be minimized by the choice of constituting materials, controlling radiation losses is often a bigger problem. Recent solutions include the use of coupled radiant and sub-radiant modes yielding narrow asymmetric Fano resonances in a wide range of systems, from defect states in photonic crystals and optical waveguides with mesoscopic ring resonators to nanoscale plasmonic and metamaterial systems exhibiting interference effects akin to electromagnetically-induced transparency. Here we demonstrate theoretically and confirm experimentally a new mechanism of resonant electromagnetic transparency, which yields very narrow isolated symmetric Lorentzian transmission lines in toroidal metamaterials. It exploits the long sought non-trivial non-radiating charge-current excitation based on interfering electric and toroidal dipoles that was first proposed by Afanasiev and Stepanovsky in [J. Phys. A Math. Gen. 28, 4565 (1995)].

Highlights

Engaging strongly resonant interactions allows dramatic enhancement of functionalities of many electromagnetic devices
In a spherical coordinate system, magnetic multipoles are defined by transversal components of oscillating current density, while electric multipoles are attributed to oscillating charge density
The poloidal currents are proportional to the time derivative of the charge displacement and produce toroidal moment T~(t)~Teiv t* m ivr0eiv t that is oriented along m and oscillates coherently with the electric dipole lagging a quarter of the period behind the latter

Summary

Introduction

Engaging strongly resonant interactions allows dramatic enhancement of functionalities of many electromagnetic devices. We demonstrate theoretically and confirm experimentally a new mechanism of resonant electromagnetic transparency, which yields very narrow isolated symmetric Lorentzian transmission lines in toroidal metamaterials. It exploits the long sought non-trivial non-radiating charge-current excitation based on interfering electric and toroidal dipoles that was first proposed by Afanasiev and Stepanovsky in [J. These radial components of the current density give rise to an additional independent family of elementary radiation sources, the dynamic toroidal multipoles, which are physically rather than just semantically different from the conventional magnetic and electric multipoles[6,7]. Since microwave and optical toroidal resonances were identified in a number of metamaterial and plasmonic systems[13,14,15,16]

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