# Interlayer Topological Transport and Devices based on Layer Pseudospins in Photonic Valley-Hall Phases

## TL;DR

This paper demonstrates the existence of layer pseudospins in photonic valley-Hall phases using coupled surface plasmon crystals, enabling topological photonic devices that manipulate signals based on this new degree of freedom.

## Contribution

It introduces the realization of layer pseudospins in photonic systems and demonstrates topological devices utilizing this property, expanding topological insulator concepts beyond quantum systems.

## Key findings

- Layer pseudospins are observed in photonic valley-Hall phases.
- Topological devices like layer convertors and delay lines are experimentally demonstrated.
- Negligible thermal and radiative losses enable clear observation of topological phenomena.

## Abstract

Valley-Hall phases, first proposed in two-dimensional (2D) materials, originate from nontrivial topologies around valleys which denote local extrema in momentum space. Since they are extended into classical systems, their designs draw inspirations from existing quantum counterparts, and their transports show similar topological protections. In contrast, it is recently established in acoustics that layer pseudospins in valley-Hall phases can give rise to special valley-Hall edge states with fundamentally different transport behaviors at the interfaces compared with various 2D materials. Their realization in other classical systems, such as photonics, would allow us to design topological insulators beyond quantum inspirations. In this work, we show that layer pseudospins exist in photonic valley-Hall phases, using vertically coupled designer surface plasmon crystals, a non-radiative system in open environment supporting tightly-confined propagating modes. The negligible thermal and radiative losses in our structure pave the way for our direct observations of the layer pseudospins and associated topological phenomena stemmed from them in both real and reciprocal spaces. Photonic devices that manipulate signals based on layer pseudospins of the topological phases, such as layer convertors and layer-selected delay lines, are experimentally demonstrated, confirming the potential applications of layer pseudospins as a new degree of freedom carrying information.

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Source: https://tomesphere.com/paper/1812.06198