Quasi-bound states in the continuum induced by $\mathcal{P}\mathcal{T}$-symmetry breaking

Abstract

Bound states in the continuum (BICs) enable unique features in tailoring light-matter interaction on nanoscale. These radiationless localized states drive theoretically infinite quality factors and lifetimes for modern nanophotonics, making room for a variety of emerging applications. Here we use the peculiar properties possessed by the so-called $\mathcal{P}\mathcal{T}$-symmetric optical structures to propose the novel mechanism for the quasi-BIC manifestation governed by the $\mathcal{P}\mathcal{T}$-symmetry breaking. In particular, we study regularities of the spontaneous $\mathcal{P}\mathcal{T}$-symmetry breaking in trilayer structures with the outer loss and gain layers consisting of materials with permittivity close to zero. We reveal singular points on the curves separating $\mathcal{P}\mathcal{T}$-symmetric and broken-$\mathcal{P}\mathcal{T}$-symmetry states in the parametric space of the light frequency and the angle of incidence. These singularities remarkably coincide with the BIC positions at the frequency of volume plasmon excitation, where the dielectric permittivity vanishes. The loss and gain value acts as an asymmetry parameter that disturbs conditions of the ideal BIC inducing the quasi-BIC. Fascinating properties of these quasi-BICs having ultrahigh quality factors and almost perfect transmission can be utilized in sensing, nonlinear optics, and other applications.

arXiv comment12 pages, 14 figures

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Cited by in corpus (5)

• Applications of Bound States in the Continuum in Photonics
• Fixed points on band structures of non-Hermitian models: Extended states in the bandgap and ideal superluminal tunneling
• Synthesizing quasi-bound states in the continuum in epsilon-near-zero layered materials
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• Trapped-mode excitation in all-dielectric metamaterials with loss and gain