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Infomat: anisotropic polaritons in van der Waals materials

wallpapers News 2020-08-06
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polaritons refer to the interaction between the excitons the elementary excitation of the dielectric constant in the material the strong coupling between the photons the resonant charges in the material. Polaritons can be classified as plasmon polaritons exciton polaritons phonon polaritons (PHPs) according to the interaction between light matter. For PHPs we consider the dielectric constant tensor ϵ = diag [ϵ x ϵ y ϵ Z] due to its phonon coupling properties. When there is anisotropy in crystal there will also be anisotropy in dielectric constant. When ϵ I (I = x y z) is opposite to the other two terms it is called hyperbolic dielectric material. Taking hexagonal boron nitride (hBN) as an example where ϵ x = ϵ y = ϵ⊥ 0 ϵ z = ϵ∥ 0 the in-plane propagation of excitons in the material is isotropic but the out of plane propagation is hyperbolic. This is the key problem of a series of optical phenomena technologies such as negative refractive index hyper prism nano lithography quantum radiation enhancement so on. Traditionally in order to achieve negative refractive index characteristics it is necessary to design fine metamaterial structures (such as open resonator ring Ω - oscillator). But recently in natural anisotropic two-dimensional materials such as α - MoO3 researchers found that ϵ x ⋅ y < 0 observed the ellipsoidal or hyperbolic propagation characteristics of polaritons in the plane. The introduction of anisotropic van der Waals materials has realized the low loss of polaritons dynamic control of polarization selection which is also a difficult problem in traditional metamaterial structure design.

the Bao bridge team of Monash University in Australia focusing on polaritons was invited to publish a review entitled "anaerobic polaritons in van der Waals materials" in infomat a highly influential journal in the field of information materials newly launched by Wiley publishing group. This paper summarizes the recent research progress of the near-field response of planar anisotropic polaritons focuses on the introduction of natural layered materials which may have greater potential than traditional materials in some frequency ranges. Firstly the imaging mechanism of scattering scanning near-field optical microscope (s-SNOM) in real space the research progress of polaritons in two-dimensional materials are introduced. Then the relation between anisotropic polaritons hyperbolic / elliptic dispersion is discussed. After a brief review of the hyperbolic hypersurface structure the author focuses on the in-plane anisotropy in natural layered materials. Based on this characteristic some potential applications of optical modulators are proposed. Van der Waals in-plane anisotropic materials thus establish a new paradigm in nanophotonics especially in the nano scale to achieve the direction control of light conduction light matter interaction.


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