Axions, surface states, and the post constraint in electromagnetics

Lakhtakia, Akhlesh; Mackay, Tom G.

doi:10.1117/12.2190105

Cited by 5 publications

(3 citation statements)

References 32 publications

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“…This impasse can be resolved on realizing that surface states exist on topological insulators as protected conducting states, and the characteristic behavior of these materials is due to those surface states. Furthermore, Ψ vanishes from the Maxwell equations ( 5) applicable to V in occupied by the topological insulator; indeed, Ψ would vanish even if the topological insulator were bianisotropic [8]. For both of these reasons, we must choose model II, which also satisfies the Post constraint Ψ ≡ 0 [9].…”

Section: A Fundamental Boundary-value Problemmentioning

confidence: 99%

Classical electromagnetic model of surface states in topological insulators

Lakhtakia

Mackay

2016

J. Nanophoton

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Abstract. A topological insulator is classically modeled as an isotropic material with a magnetoelectric pseudoscalar Ψ existing in its bulk while its surface is charge free and current free. An alternative model is obtained by setting Ψ ≡ 0 and incorporating surface charge and current densities characterized by an admittance γ. Analysis of planewave reflection and refraction due to a topological-insulator half space reveals that the parameters Ψ and γ arise identically in the reflection and transmission coefficients, implying that the two classical models cannot be distinguished on the basis of any scattering scenario. However, as Ψ disappears from the Maxwell equations applicable to any region occupied by the topological insulator, and because surface states exist on topological insulators as protected conducting states, the alternative model must be chosen. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Section: A Fundamental Boundary-value Problemmentioning

confidence: 99%

Classical electromagnetic model of surface states in topological insulators

Lakhtakia

Mackay

2016

J. Nanophoton

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“…More recently axionic responses have also been proposed [16] and observed [17] in topological insulators. Observations are, however, still controversial, with claims that evidence of violation of the so-called Post constraint [18] can be explained by an admittance that describes surface states [19]. In the domain of particle physics, axions have been proposed as candidates for dark matter [20], but as yet no particle axions have been observed.…”

Section: Introductionmentioning

confidence: 99%

Temporary Singularities and Axions: an analytic solution that challenges charge conservation

Gratus,

Kinsler,

McCall

2020

Preprint

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We construct an analytic solution to Maxwell's equations that violates global charge conservation, by building on the possibilities demonstrated in [Foundations of Physics 49, 330 (2019)]. The construction is valid for a spacetime containing a temporary singularity and a Maxwellian electrodynamics containing a "topological" axion field. As such, it demonstrates that although "physics breaks down" at a singularity, the physical laws on the spacetime still impose constraints on what can happen. Further, the concepts of transformation optics can be applied to show that our specific mathematical solution has a much wider applicability.

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“…II. The topological insulator is an isotropic dielectric-magnetic material characterized by the relative permittivity ε r and the relative permeability µ r , but its surface is endowed with surface charge and current densities quantitated through a non-null surface admittance γ [20].…”

Section: Introductionmentioning

confidence: 99%

Electromagnetic scattering by homogeneous, isotropic, dielectric–magnetic sphere with topologically insulating surface states

Lakhtakia

Mackay

2016

J. Opt. Soc. Am. B

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The Lorenz-Mie formulation of electromagnetic scattering by a homogeneous, isotropic, dielectricmagnetic sphere was extended to incorporate topologically insulating surface states characterized by a surface admittance γ. 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 γ, when the sphere is either nondissipative or weakly dissipative. For large values of γ, 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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Axions, surface states, and the post constraint in electromagnetics

Cited by 5 publications

References 32 publications

Classical electromagnetic model of surface states in topological insulators

Classical electromagnetic model of surface states in topological insulators

Temporary Singularities and Axions: an analytic solution that challenges charge conservation

Electromagnetic scattering by homogeneous, isotropic, dielectric–magnetic sphere with topologically insulating surface states

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