Abstract
Toroidal multipoles are the subject of growing interest because of their unusual electromagnetic properties different from the electric and magnetic multipoles. In this paper, we present two new related classes of plasmonic metamaterial composed of purposely arranged of four U-shaped split ring resonators (SRRs) that show profound resonant toroidal responses at optical frequencies. The toroidal and magnetic responses were investigated by the finite-element simulations. A phenomenon of reversed toroidal responses at higher and lower resonant frequencies has also been reported between this two related metamaterials which results from the electric and magnetic dipoles interaction. Finally, we propose a physical model based on coupled LC circuits to quantitatively analyze the coupled system of the plasmonic toroidal metamaterials.
Highlights
Toroidal resonance is created by currents flowing on a surface of a doughnut-shaped structure along its meridians which was first reported by Zel’dovich (1957) in nuclear physics to explain the parity violation of the weak interaction force [1]
Metamaterials are created as an array of artificial sub-wavelength structures, often exhibit unique optical properties through electric and magnetic dipole resonance which are not found in nature
We present two types of toroidal metamaterials, functionality of which is underpinned by the resonant plasmonic responses of purposely arranged U-shaped split ring resonators (SRRs)
Summary
Toroidal resonance is created by currents flowing on a surface of a doughnut-shaped structure along its meridians which was first reported by Zel’dovich (1957) in nuclear physics to explain the parity violation of the weak interaction force [1]. Metamaterials are created as an array of artificial sub-wavelength structures, often exhibit unique optical properties through electric and magnetic dipole resonance which are not found in nature. Split ring resonator (SRR) is the most common structure of metamaterial, showing artificial magnetism [7,8,9,10], optical chirality [11,12], negative refraction index [13,14] and allowing for optical spectrum manipulation [15,16,17,18,19]. In 2010, toroidal response in microwave region was first experimentally demonstrated and separated from other multipoles by arranging four three-dimensional resonant split metallic wire loops in a unit cell of toroidal symmetry by T. The proposed metamaterial structures that we investigate in the present work are the first example of artificial media exhibiting a clear toroidal signature in the optical part of the spectrum
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