Hyperbolic hybrid waves and optical topological transitions in few-layer anisotropic metasurfaces

TL;DR

This paper develops a formalism to analyze hybrid surface electromagnetic waves in anisotropic metasurfaces, predicting novel hyperbolic polaritons, topological transitions, and strong confinement effects with potential applications in optical technologies.

Contribution

A generalized 4x4 T-matrix formalism for anisotropic 2D layers is introduced, enabling detailed analysis of hybrid surface wave dispersions and topological transitions.

Findings

Prediction of hyperbolic plasmon-exciton polaritons.

Identification of hyperbolic acoustic waves with strong confinement.

Discovery of topological transitions in iso-frequency contours.

Abstract

A comprehensive analysis of hybrid TM-TE polarized surface electromagnetic waves supported by different few-layer anisotropic metasurfaces is presented. A generalized 4$\times$4 T-matrix formalism for arbitrary anisotropic 2D layers is developed, from which the general relations for the surface waves dispersions and scattering coefficients are deduced. Using this formalism and the effective conductivity approach, the dispersions and iso-frequency contours (IFCs) topology of the surface waves in various hybrid uniaxial metasurfaces are studied. The existence of hyperbolic plasmon-exciton polaritons in plasmon-exciton hybrids and hyperbolic acoustic waves with strong confinement in both out-of-plane and in-plane directions in uniaxial plasmonic bilayers are predicted. In plasmonic uniaxial metasurfaces on metal films, the elliptic and hyperbolic backward surface waves with negative group velocity are predicted and additional topological transitions in both elliptic and hyperbolic IFCs of the hybrid surface waves are revealed. Ultrathin twisted uniaxial plasmonic bilayers are proposed as systems with the IFCs topological transitions highly sensitive to the layers twist. The developed formalism may become a useful tool in the calculation of multifunctional few-layer metasurfaces or van der Waals heterostructures based on 2D materials with in-plane anisotropy, where the TM-TE polarization mixing must be considered. The predicted effects may open new horizons in the development and applications of planar optical technologies.