# Type-I hyperbolic metasurfaces for highly-squeezed designer polaritons with negative group velocity

## TL;DR

This paper introduces a type-I hyperbolic metasurface supporting highly-squeezed magnetic polaritons with negative group velocity, enabling ultra-compact polariton circuits and broad applications in nanophotonics.

## Contribution

It proposes a scalable hyperbolic metasurface design supporting magnetic polaritons, demonstrating experimental ultra-compact polariton circuits with novel waveguiding capabilities.

## Key findings

- Effective refractive index up to 60
- Group velocity reduced to 1/400 of light speed
- 3600-fold reduction in device footprint

## Abstract

Hyperbolic polaritons in van der Waals materials and metamaterial heterostructures provide unprecedented control over light-matter interaction at the extreme nanoscale. Here, we propose a concept of type-I hyperbolic metasurface supporting highly-squeezed magnetic designer polaritons, which act as magnetic analogues to hyperbolic polaritons in the hexagonal boron nitride (h-BN) in the first Reststrahlen band. Comparing with the natural h-BN, the size and spacing of the metasurface unit cell can be readily scaled up (or down), allowing for manipulating designer polaritons in frequency and in space at will. Experimental measurements display the cone-like hyperbolic dispersion in the momentum space, associating with an effective refractive index up to 60 and a group velocity down to 1/400 of the light speed in vacuum. By tailoring the proposed metasurface, we experimentally demonstrate an ultra-compact (with a footprint shrunken by 3600 times) integrated designer polariton circuit including high-transmission 90{\deg} sharp bending waveguides and waveguide splitters. The designed metasurface with a low profile, lightweight, and ease of access, can serve as an alternatively promising platform for emerging polaritonics, and may find many other potential applications, such as waveguiding, sensing, subdiffraction focusing/imaging, low-threshold Cherenkov radiation, strong magnetic transition enhancement, wireless energy transfer, and so forth.

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Source: https://tomesphere.com/paper/1812.06436