Sharp Toroidal Resonances in Planar Terahertz Metasurfaces

Gupta, Manoj; Savinov, Vassili; Xu, Ningning; Cong, Longqing; Dayal, Govind; Wang, Shuang; Zhang, Weili; Zheludev, Nikolay I.; Singh, Ranjan

doi:10.1002/adma.201601611

Cited by 168 publications

(118 citation statements)

References 37 publications

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“…In the literature, external light, with either linear [129], radial [105,130], or circular polarization [101,109], has been used to illuminate the metamaterials normally, laterally, or obliquely (see Figure 6). …”

Section: External Lightmentioning

confidence: 99%

Theory and applications of toroidal moments in electrodynamics: their emergence, characteristics, and technological relevance

2017

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Dipole selection rules underpin much of our understanding in characterization of matter and its interaction with external radiation. However, there are several examples where these selection rules simply break down, for which a more sophisticated knowledge of matter becomes necessary. An example, which is increasingly becoming more fascinating, is macroscopic toroidization (density of toroidal dipoles), which is a direct consequence of retardation. In fact, dissimilar to the classical family of electric and magnetic multipoles, which are outcomes of the Taylor expansion of the electromagnetic potentials and sources, toroidal dipoles are obtained by the decomposition of the moment tensors. This review aims to discuss the fundamental and practical aspects of the toroidal multipolar moments in electrodynamics, from its emergence in the expansion set and the electromagnetic field associated with it, the unique characteristics of their interaction with external radiations and other moments, to the recent attempts to realize pronounced toroidal resonances in smart configurations of meta-molecules. Toroidal moments not only exhibit unique features in theory but also have promising technologically relevant applications, such as data storage, electromagnetic-induced transparency, unique magnetic responses and dichroism.

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Section: External Lightmentioning

confidence: 99%

Theory and applications of toroidal moments in electrodynamics: their emergence, characteristics, and technological relevance

2017

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“…Initially, evidence of toroidal response was seen in a chiral metamaterial-an array of wire helix bent into a torus [117]-but the announcement had to wait until 2010, when we clearly saw a toroidal dipole response by detecting a resonant toroidal electromagnetic response in an artificially engineered metamaterial [118]. Observations of toroidal response in terahertz [119], optical plasmonic [120][121][122] and dielectric metamaterials [123] followed soon together with the developing theory [124].…”

Section: Developing Metamaterials Technology: Switching and Tunabilitymentioning

confidence: 99%

“…From 1998 onward, we worked on nanoscale structural transformations as a source of optical nonlinearity and nonvolatile switching [5], with keen interest in using them for photonic technologies. We realized that phase-change functionality could provide a way of shrinking optical switching devices to the nanoscale [50], and later that it could be used to control the individual molecules of metamaterials [51]. Indeed, the modulation of a signal requires that its amplitude or phase be changed substantially by a control signal, through a change in either propagation losses or propagation delays.…”

Section: Developing Metamaterials Technology: Switching and Tunabilitymentioning

confidence: 99%

“…We harnessed nonvolatile, amorphous-crystalline transitions in the chalcogenide phase-change medium germanium antimony telluride to realize optically switchable, all-dielectric metamaterials that provided reflectivity and transmission switching contrast ratios of up to 5:1 at visible/near-infrared wavelengths selected by design. We also demonstrated that dielectric metamaterials can be written, erased and rewritten as two-dimensional binary or greyscale patterns into a nanoscale film of phase-change material by inducing a refractive-index-changing phase transition with tailored trains of femtosecond pulses [51]. In collaboration with Professor Brian Hayden from Southampton's Department of Chemistry -a pioneer and global leader in the field of 'high-throughput materials discovery'-and colleagues in Singapore, we continue to explore new plasmonic and dielectric materials including chalcogenides, superconductors, topological insulators [71] and perovskites [103].…”

Section: Developing Metamaterials Technology: Switching and Tunabilitymentioning

confidence: 99%

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Metamaterials at the University of Southampton and beyond

Zheludev¹

2017

J. Opt.

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At the University of Southampton, research on metamaterials started in 2000 with a paper describing a metallic microstructure, comprising an ensemble of fully metallic 'molecules'. In the years since then, metamaterials have evolved from an approach for designing unusual electromagnetic properties by structuring matter at the sub-wavelength scale to become a universal paradigm for active functional media with optical properties on demand at any given point in time and space. Metamaterials are now recognized as a promising enabling technology and one of the most buoyant and exciting research disciplines at the crossroads between photonics and nanoscience. Many 'made in Southampton' concepts have influenced the global research community, and we are now working in collaboration with our sister research centre in Nanyang Technological University, Singapore. In this article, I provide a historical overview of the metamaterials research field, from early studies to recent developments through the lens of the Southampton group, and discuss promising future directions.

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“…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].…”

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confidence: 99%

Blueshift and phase tunability in planar THz metamaterials: the role of losses and toroidal dipole contribution

2017

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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 ...

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Sharp Toroidal Resonances in Planar Terahertz Metasurfaces

Cited by 168 publications

References 37 publications

Theory and applications of toroidal moments in electrodynamics: their emergence, characteristics, and technological relevance

Theory and applications of toroidal moments in electrodynamics: their emergence, characteristics, and technological relevance

Metamaterials at the University of Southampton and beyond

Blueshift and phase tunability in planar THz metamaterials: the role of losses and toroidal dipole contribution

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