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The Lorenz--Mie formulation of electromagnetic scattering by a homogeneous, isotropic, dielectric-magnetic sphere was extended to incorporate topologically insulating surface states characterized by a surface admittance $gamma$. Closed-form expressions were derived for the expansion coefficients of the scattered field phasors in terms of those of the incident field phasors. These expansion coefficients were used to obtain analytical expressions for the total scattering, extinction, forward scattering, and backscattering efficiencies of the sphere. Resonances exist for relatively low values of $gamma$, when the sphere is either nondissipative or weakly dissipative. For large values of $gamma$, the scattering characteristics are close to that of a perfect electrically conducting sphere, regardless of whether the sphere is composed of a dissipative or nondissipative material, and regardless of whether that material supports planewave propagation with positive or negative phase velocity.
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The propagation of electromagnetic surface waves guided by the planar interface of two isotropic chiral materials, namely materials $calA$ and $calB$, was investigated by numerically solving the associated canonical boundary-value problem. Isotropic chiral material $calB$ was modeled as a homogenized composite material, arising from the homogenization of an isotropic chiral component material and an isotropic achiral, nonmagnetic, component material characterized by the relative permittivity $eps_a^calB$. Changes in the nature of the surface waves were explored as the volume fraction $f_a^calB$ of the achiral component material varied. Surface waves are supported only for certain ranges of $f_a^calB$; within these ranges only one surface wave, characterized by its relative wavenumber $q$, is supported at each value of $f_a^calB$. For $mbox{Re} lec eps_a^calB ric > 0 $, as $left| mbox{Im} lec eps_a^calB ric right|$ increases surface waves are supported for larger ranges of $f_a^calB$ and $left| mbox{Im} lec q ric right|$ for these surface waves increases. For $mbox{Re} lec eps_a^calB ric < 0 $, as $ mbox{Im} lec eps_a^calB ric $ increases the ranges of $f_a^calB$ that support surface-wave propagation are almost unchanged but $ mbox{Im} lec q ric $ for these surface waves decreases. The surface waves supported when $mbox{Re} lec eps_a^calB ric < 0 $ may be regarded as akin to surface-plasmon-polariton waves, but those supported for when $mbox{Re} lec eps_a^calB ric > 0 $ may not.
In this research, we report the experimental evidence of the directional Fano resonances at the scattering of a plane, linearly polarized electromagnetic wave by a homogeneous dielectric sphere with high refractive index and low losses. We observe a typical asymmetric Fano profile for the intensity scattered in, practically, any given direction, while the overall extinction cross section remains Lorentzian. The phenomenon is originated in the interference of the selectively excited electric dipolar and quadrupolar modes. The selectivity of the excitation is achieved by the proper choice of the frequency of the incident wave. Thanks to the scaling invariance of the Maxwell equations, in these experiments we mimic the scattering of the visible and near IR radiation by a nanoparticle made of common superconductor materials (Si, Ge, GaAs, GaP) by the equivalent scattering of a spherical particle of 18 mm in diameter in the microwave range. The theory developed to explain the experiments extends the conventional Fano approach to the case when both interfering partitions are resonant. The perfect agreement between the experiment and the theory is demonstrated.
The goal of this paper is to present a previously published work [1] in an errorless form. The work has studied the scattering of electromagnetic plane wave by an impedance strip placed in homogeneous isotropic chiral medium using Kobayashi Potential (KP) method; that has been an important, valuable and attractive investigation in the electromagnetic scattering, especially in KP method. Unfortunately, the study has some basic errors that prevent interesting readers from understanding the investigation. Finally, the formulation of this paper is validated by [2].
The electromagnetic scattering properties of topological insulator (TI) spheres are systematically studied in this paper. Unconventional backward scattering caused by the topological magneto-electric (TME) effect of TIs are found in both Rayleigh and Mie scattering regimes. This enhanced backward scattering can be achieved by introducing an impedance-matched background which can suppress the bulk scattering. For the cross-polarized scattering coefficients, interesting antiresonances are found in the Mie scattering regime, wherein the cross-polarized electromagnetic fields induced by the TME effect are trapped inside TI spheres. In the Rayleigh limit, the quantized TME effect of TIs can be determined by measuring the electric-field components of scattered waves in the far field.
Motivated by the theoretical observation that isotropic chirality can exist even in completely random systems, we design a dielectric metamaterial consisting of a random colloid of meta-atoms, which exhibits unprecedentedly high isotropic optical activity. Each meta-atom is composed of a helically arranged cluster of silicon nanospheres. Such clusters can be fabricated by large-scale DNA self-assembly techniques. It is demonstrated that the use of a high concentration of the meta-atoms in the colloid provides significant suppressions of incoherent scattering losses. As a result, the proposed system shows three orders of magnitude improvement of isotropic optical activity as compared with the previous metamaterial designs. This work highlights the significant potential of completely random system, which are commonly produced in colloidal sciences, for applications as metamaterials towards novel photonic effects and devices.
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