Near-zero Permittivity Research Articles

Two Types of Localized States in a Photonic Crystal Bounded by an Epsilon near Zero Nanocomposite

The spectral properties of a one-dimensional photonic crystal bounded by a resonant absorbing nanocomposite layer with the near-zero permittivity have been studied. The problem of calculating the transmittance, reflectance, and absorptance spectra of such structures at the normal and oblique incidence of light has been solved. It is shown that, depending on the permittivity sign near zero, the nanocomposite is characterized by either metallic or dielectric properties. The possibility of simultaneous formation of the Tamm plasmon polariton at the photonic crystal/metallic nanocomposite interface and the localized state similar to the defect mode with the field intensity maximum inside the dielectric nanocomposite layer is demonstrated. Specific features of field localization at the Tamm plasmon polariton and defect mode frequencies are analyzed.

Design Anisotropic Broadband ϵ -Near-Zero Metamaterials: Rigorous Use of Bergman and Milton Spectral Representations

Designing metamaterials with near-zero electric permittivity (ENZ) is of great importance for practical applications at optical frequencies, but designs based on traditional approaches are restricted to a narrow range of operating frequencies. The authors invoke the rigorous spectral representation of the effective permittivity for a composite system, treating the design challenge as an inverse problem of effective-medium theory. Their approach, based on analytical solution of the inverse problem plus finite-element simulations, may be the way forward to broadband ENZ metamaterials.

High-selective band-reject FSS with dual-band near-zero refractive index based on complementary dual-layer symmetry resonator-ring

A new band-reject frequency-selective surface (FSS) based on dual-band near-zero refractive index metamaterial (ZIM) design is presented in this paper. Consisting of a planar array of complementary dual-layer symmetry resonant ring, the proposed FSS exhibits a high-selective band-reject filtering response. From the viewpoint of effective medium, the subwavelength FSS is characterized by near-zero effective magnetic permeability and near-zero effective electric permittivity in two different operational bands, respectively. The corresponding resonant behavior and E-field distributions are analyzed in detail. A prototype of the proposed FSS working in X-band is fabricated and measured. The simulation and experiment results verify the effectiveness and correctness of the ZIM-based design method.

Compressibility-near-zero acoustic supercoupling

Epsilon-near-zero supercoupling is a widely-researched topic in electromagnetics. This phenomenon takes advantage of media with near-zero dielectric permittivity to build waveguide coupling channels which can, in principle, support unitary transmission and complete phase uniformity, independent of the length and height of the coupling channel. In this effort, we present the possibility that an analogous, extraordinary coupled-mode phenomenon exists in acoustics, which we call compressibility-near-zero (CNZ) supercoupling. Prior works have required the presence of periodic membrane resonances in order to observe near-zero index coupling. We have shown, for the first time, theoretically and experimentally, that the phenomenon can be observed without the use of membranes. We envision this development as a first step towards experimentally realizing spatiotemporally-modulated acoustic non-reciprocal devices which take advantage of these physical principles.

Light-induced “plasmonic” properties of organic materials: Surface polaritons and switching waves in bistable organic thin films

Purely organic materials with negative and near-zero dielectric permittivity can be easily fabricated, and the propagation of surface polaritons at the material/air interface was demonstrated. Here, we develop a theory of nonlinear light-induced “plasmonic” properties of organic materials. We predict the generation of switching waves or kinks in the bistable organic thin films that enable us to observe a bistable behaviour of the surface polaritons at the organic thin film/dielectric interface under laser irradiation. We present the alternating-sign dependence of the switching wave velocity on pump intensity and discuss a possibility of controlling the polariton propagation by switching waves.

Particular features of the optical properties of an anisotropic metamaterial with a near-zero dielectric permittivity

The propagation of an electromagnetic wave through a layer of a uniaxial anisotropic metamaterial with the components of its permittivity tensor close to zero and the reflection of the wave from the layer have been considered. The occurrence of transmission maxima of the electromagnetic wave at specific angles of incidence has been confirmed. It has been shown that, when studying this effect, one cannot neglect the absorption, because this neglecting leads to unrealistic predictions, such as a total transmission of the wave by the layer of the anisotropic metamaterial at special angles of incidence of the wave.

An ideal dielectric coat to avoid prosthesis RF-artefacts in Magnetic Resonance Imaging

The number of people submitted to total hip or knee arthroplasty increased in the last years and it is likely to grow further. Hence, the importance of a proper investigation tool that allows to determine and recognize the potential presence of perioperative and/or postoperative diseases becomes clear. Although the Magnetic Resonance Imaging (MRI) technique demonstrated several advantages over the other common tomography tools, it suffers from the arise of image artefacts if it is performed in presence of metallic prostheses. In particular, the so-called RF-artefacts are caused by the inhomogeneity in the radiofrequency magnetic field of MRI, due to the electric currents induced on the metal surface by the field itself. In this work, a near-zero permittivity dielectric coat is simulated to reduce those currents and, therefore, the RF-artefacts onset in the final image. Numerical results confirm that the dielectric coat strongly reduces the magnetic field inhomogeneity, suggesting a possible solution to a well-known problem in the MRI field.

Near-zero refractive index photonics

The underlying principles and unique optical applications of structures exhibiting near-zero dielectric permittivity and/or magnetic permeability are reviewed. The timely relevance to nonlinear, non-reciprocal and non-local effects is highlighted.

Dispersivity of Balanced Near-Zero Permittivity and Permeability (EMNZ) Medium

$\epsilon $ -near-zero (ENZ), $\mu $ -near-zero (MNZ), and $\epsilon $ -and- $\mu $ -near-zero (EMNZ) materials all exhibit the property of $n=\sqrt {\epsilon _{r}\mu _{r}}\approx 0$ . The wave impedance $Z=({\mu /{\epsilon }})^{1/2}$ , though, is different for the different materials. For the EMNZ, the impedance can remain finite, in contrast to the ENZ and MNZ materials. Therefore, the electric and magnetic fields within the EMNZ can remain coupled, unlike the ENZ and MNZ. This paper presents an analysis of dispersivity in an EMNZ layer under the condition of balance $\mu _{r}=\epsilon _{r}$ . One possible application for this condition is seen in the analysis of transmission and reflection from an EMNZ–free space interface, which reveals that a perfect match condition is possible for normal incidence, while for any other incidence angle, this interface is a perfect reflector.

Graphene-based extremely wide-angle tunable metamaterial absorber.

We investigate the absorption properties of graphene-based anisotropic metamaterial structures where the metamaterial layer possesses an electromagnetic response corresponding to a near-zero permittivity. We find that through analytical and numerical studies, near perfect absorption arises over an unusually broad range of beam incidence angles. Due to the presence of graphene, the absorption is tunable via a gate voltage, providing dynamic control of the energy transmission. We show that this strongly enhanced absorption arises due to a coupling between light and a fast wave-mode propagating along the graphene/metamaterial hybrid.

Zero-Index Platforms: Where Light Defies Geometry

Geometry-invariant effects in structures with near-zero permittivity or permeability could lead to deformable optical devices, and to new insights into unique light-matter interactions.

Repulsion of polarised particles from anisotropic materials with a near-zero permittivity component.

Reduction of adhesion and stiction is crucial for robust operation on nanomechanical and optofluidic devices as well as atom and molecule behaviour near surfaces. It can be achieved using electric charging, magnetic materials or light pressure and optical trapping. Here we show that a particle scattering or emitting in close proximity to an anisotropic substrate can experience a repulsive force if one of the diagonal components of the permittivity tensor is close to zero. We derive an analytic condition for the existence of such repulsive force depending on the optical properties of the substrate. We also demonstrate the effect using realistic anisotropic metamaterial implementations of a substrate. The anisotropic metamaterial approach using metal–dielectric and graphene–dielectric multilayers provides a tuneable spectral range and a very broad bandwidth of electromagnetic repulsion forces, in contrast to isotropic substrates.

Erratum: “Nonlinear organic plasmonics: Applications to optical control of Coulomb blocking in nanojunctions” [Appl. Phys. Lett. 107, 053302 (2015)

Purely organic materials with negative and near-zero dielectric permittivity can be easily fabricated. Here we develop a theory of nonlinear non-steady-state organic plasmonics with strong laser pulses. The bistability response of the electron-vibrational model of organic materials in the condensed phase has been demonstrated. Non-steady-state organic plasmonics enable us to obtain near-zero dielectric permittivity during a short time. We have proposed to use non-steady-state organic plasmonics for the enhancement of intersite dipolar energy-transfer interaction in the quantum dot wire that influences on electron transport through nanojunctions. Such interactions can compensate Coulomb repulsions for particular conditions. We propose the exciton control of Coulomb blocking in the quantum dot wire based on the non-steady-state near-zero dielectric permittivity of the organic host medium.

Nonlinear organic plasmonics: Applications to optical control of Coulomb blocking in nanojunctions

Purely organic materials with negative and near-zero dielectric permittivity can be easily fabricated. Here, we develop a theory of nonlinear non-steady-state organic plasmonics with strong laser pulses that enable us to obtain near-zero dielectric permittivity during a short time. Our consideration is based on the model of the interaction of strong (phase modulated) laser pulse with organic molecules developed by one of the authors before, extended to the dipole-dipole intermolecular interactions in the condensed matter. We have proposed to use non-steady-state organic plasmonics for the enhancement of intersite dipolar energy-transfer interaction in the quantum dot wire that influences on electron transport through nanojunctions. Such interactions can compensate Coulomb repulsions for particular conditions. We propose the exciton control of Coulomb blocking in the quantum dot wire based on the non-steady-state near-zero dielectric permittivity of the organic host medium.

Roles of epsilon-near-zero (ENZ) and mu-near-zero (MNZ) materials in optical metatronic circuit networks.

The concept of metamaterial-inspired nanocircuits, dubbed metatronics, was introduced in [Science 317, 1698 (2007); Phys. Rev. Lett. 95, 095504 (2005)]. It was suggested how optical lumped elements (nanoelements) can be made using subwavelength plasmonic or non-plasmonic particles. As a result, the optical metatronic equivalents of a number of electronic circuits, such as frequency mixers and filters, were suggested. In this work we further expand the concept of electronic lumped element networks into optical metatronic circuits and suggest a conceptual model applicable to various metatronic passive networks. In particular, we differentiate between the series and parallel networks using epsilon-near-zero (ENZ) and mu-near-zero (MNZ) materials. We employ layered structures with subwavelength thicknesses for the nanoelements as the building blocks of collections of metatronic networks. Furthermore, we explore how by choosing the non-zero constitutive parameters of the materials with specific dispersions, either Drude or Lorentzian dispersion with suitable parameters, capacitive and inductive responses can be achieved in both series and parallel networks. Next, we proceed with the one-to-one analogy between electronic circuits and optical metatronic filter layered networks and justify our analogies by comparing the frequency response of the two paradigms. Finally, we examine the material dispersion of near-zero relative permittivity as well as other physically important material considerations such as losses.

Miniaturization of 3-D Anistropic Zero-Refractive-Index Metamaterials With Application to Directive Emissions

Several strategies are explored for the first time toward the miniaturization of three-dimensional (3-D) anistropic zero-refractive-index metamaterials (AZIM). By incorporating the fractal, spiral, and meandered resonant metallic inclusions within a host dielectric medium, several AZIM elements are engineered in subwavelength at the plasma frequency. The influences of geometrical shape, arrangement, and dimensions of inclusions on electromagnetic features of the 3-D elements are also investigated to obtain the design guideline. In this frame, we have designed a set of AZIM elements with near-zero permittivity and near-zero permeability occurring at the same frequency. To demonstrate potential applications, a lens horn antenna by loading the 3-D AZIM lens has been designed, fabricated, and measured. Numerical and experimental results agree well and illustrate that the beamwidth of the E-plane pattern has reduced about 4.9 $^{\circ}$ while that of the H plane has reduced about 6.7 $^{\circ}$ . Moreover, the gain of the lens horn antenna has improved 1.6 dB relative to its conventional counterpart with identical aperture. The proposed avenue in 3-D AZIM design advances a step toward the compactness and homogenization.

Arbitrary Control of Electromagnetic Flux in Inhomogeneous Anisotropic Media with Near-Zero Index

We propose a method to control electromagnetic flux in an almost arbitrary way in wavelength and subwavelength scales. The capability of subwavelength flux control is enabled by the evanescent waves induced in a class of inhomogeneous anisotropic media with a near-zero permittivity component. By designing the spatial profile of the other permittivity component in such inhomogeneous media, the flow and distribution of energy flux can be conveniently manipulated. This method provides another approach to efficiently control electromagnetic flux in nonmagnetic media.

Nonlinear dynamics in low permittivity media: the impact of losses

Slabs of materials with near-zero permittivity display enhanced nonlinear processes. We show that field enhancement due to the continuity of the longitudinal component of the displacement field drastically enhances harmonic generation. We investigate the impact of losses with and without bulk nonlinearities and demonstrate that in the latter scenario surface, magnetic and quadrupolar nonlinear sources cannot always be ignored.

Below-Cutoff Propagation in Metamaterial-Lined Circular Waveguides

This paper investigates the propagation characteristics of circular waveguides whose interior surface is coated with a thin metamaterial liner possessing dispersive, negative, and near-zero permittivity. A field analysis of this system produces the dispersion of complex modes, and reveals in detail intriguing phenomena such as backward-wave propagation below the unlined waveguide's fundamental-mode cutoff, resonant tunneling of power, field collimation, and miniaturization. It is shown how the waveguide geometry and metamaterial parameters may be selected to engineer the lined waveguide's spectral response. Theoretical dispersion and transmission results are closely validated by full-wave simulations.

Oblique total transmissions through epsilon-near-zero metamaterials with hyperbolic dispersions

Zero-index metamaterials with near-zero permittivity and/or permeability usually reflect oblique incident waves due to total reflection that occurs at the air-metamaterial interface. In this work, we show that if one component of the near-zero–permittivity tensor of metamaterial turns from positive to negative due to a small disturbance, the dispersion surface changes dramatically from a tiny circle to a hyperbola, which enables oblique transmissions. A series of high-order total-transmission peaks at large incident angles is predicted and observed. These peaks are induced by Fabry-Pérot effects. Our work may have potential applications for filters, sensors and switches.