This paper is dedicated to a type of perforated silicon metamaterials, possessing anapole mode in visible spectral range due to destructive interference between electric and toroidal dipole moments. The proposed structure gains both in attainable material and simplified fabrication. Such a material exhibits a desirable physical effect and has obvious practical application: it supports the anapole mode without complicated 3D toroidal geometry and can be processed in one step by nanofabrication methods. The metamaterial paves the way for advanced optical devices on the base of all‐dielectric metamaterials. Besides inherently low dissipative losses and strong anapole response, such an optical metamaterial can demonstrate subtle sensing, nonradiative data transfer, Aharonov‐Bohm effect and other tempting applications in nanophotonics.

Numerous exciting optical effects in all-dielectric high-refractive-index structures are associated with so-called toroidal electrodynamics. Among these effects are anapoles, nonradiated states caused by interference phenomena, e.g. between electric dipole and toroidal dipole modes. For a spherical particle it is possible to reach simultaneous destructive interference for electric, magnetic, and corresponding toroidal dipole modes (so-called hybrid anapole mode), by varying the refractive index and/or particle size. However, there are no sufficient degrees of freedom within spherical geometry to extend the hybrid anapole mode effect to higher multipoles. Due to the optical theorem, it is also impossible to create the ideal anapole with destructive interference for all multipoles under plane wave illumination. In principle, it is possible to suppress radiation losses for the finite number of multipoles only by constructing the nanoantenna with complex geometry. Our approach of the hybrid anapole state excitation, we demonstrate in ellipsoidal all-dielectric particle providing cancellation of both electric and magnetic scattering up to quadrupole modes. This effect is achieved due to the optimised geometry of the ellipsoidal particle. Moreover, we provide classification of novel anapoles arising due to interference between moments and their mean- square radii (MSR) of electric, magnetic and toroidal family and introduce generalized anapoles for high order interaction between moments. Our concept is useful for the design of light controlling devices, reflectionless metasurfaces, high Q-factor opened resonators and nonscattering particle development.

We propose a model of tunable THz metamaterials. The main advantage is the blueshift of resonance and phase tunability due to toroidal excitation in planar metallic metamolecules with incorporated silicon inductive inclusions.Metamaterials are artificial structures with properties unattainable in natural media. Their exotic response is a promising platform for filling the THz frequency gap [1][2][3]. A separate class of metamaterials is the one with the toroidal response [4][5][6][7][8][9][10][11][12][13][14][15]. The toroidal observation is mediated by the excitation of currents flowing in inclusions of toroidal metamolecules, and resembles the poloidal currents along the meridians of gedanken torus [4,5]. Meanwhile, the destructive interference between the toroidal and electric dipole moments leads to lack the far-fields, but the fields in the metamolecule origin describing by δ-function [6,7]. Such fields configuration, referred as the anapole, allows to observe the new effect of Electromagnetically Induced Transparency (EIT) [6,7], provides an extremely high Q-factor in metamaterials [8], enables a cloaking for nanoparticles [9,10], and is a platform for confirmation of the dynamic Aharonov-Bohm effect [6,7]. Recently, it was demonstrated the anapole excitation in planar metamaterials, which enabled an extremely high Q-factor in microwave [8], which gives promising opportunities for tunable metamaterials due to the strong electromagnetic fields localization within metamolecules. In this paper, we consider a design of a metamaterial, discussed in Ref. 8, in tunable regime. For this purpose, we incorporate the photoconductive silicon into the metamolecule (Fig. 1a) and study the response of the metamaterial in the THz regime. The silicon is simulated with the permittivity εSi=11.7 and a pumppower-dependent conductivity σSi, varied from 10 -1 up to 10 6 S/m, which means transition from dielectric to metallic state. Metamolecules comprise of two split parts (Fig. 1a). The incident plane electromagnetic wave with electric field E aligned with the central wire excites conductive currents in each loop of the metamolecule. The currents form a closed vortex of magnetic field H. As a result, such configuration of electromagnetic fields supports the toroidal dipole excitation, oscillating upward and downward within metamolecule. However, the electric dipole also arises in the metamolecule and maintains the anapole mode, in accordance with the destructive interference between electric and toroidal dipole moments. The advantage is a very narrow line in the transmission spectrum of a metamaterial [8]. Here, for the first time, we consider how the planar toroidal metamolecule can be exploited as a building block for terahertz modulators. We demonstrate the blueshift and the phase tunability regime and also discuss the role of losses. The metamaterials with incorporated silicon or gallium arsenide inclusions were discussed in details as elements of modulators. The phase tunability, blueshift, redshift as well as amplitude ...

Optical Metamaterials Anapole metamaterials are desirable for non‐radiating configurations and invisibility particles in nanophotonics. However, silicon metamaterials are suitable for optics and gains in simplified fabrication due to one‐step holes for anapole mode demonstration by focused ion beam methods, for instance. In article number https://doi.org/10.1002/lpor.201800005, Alexey A. Basharin and co‐workers illustrate that these metamaterials of silicon holed clusters are suitable for anapole mode manifestation accompanied by full transparency effects.