# Direct Observation of Valley-polarized Topological Edge States in Designer Surface Plasmon Crystals

## TL;DR

This paper reports the first direct experimental visualization of valley-polarized topological edge states in a designer surface plasmon crystal, demonstrating their valley-dependent transport and topological protection in the microwave regime.

## Contribution

It introduces a novel surface plasmon crystal that acts as a valley-Hall topological insulator and provides direct visualization and confirmation of valley-polarized edge states.

## Key findings

- Valley-polarized edge states are directly visualized in the microwave regime.
- Edge states are confirmed to be fully valley-polarized via Fourier transforms.
- Topological protection at sharp corners is experimentally demonstrated.

## Abstract

The extensive research of two-dimensional layered materials has revealed that valleys, as energy extrema in momentum space, could offer a new degree of freedom for carrying information. Based on this concept, researchers have predicted valley-Hall topological insulators which could support valley-polarized edge states at non-trivial domain walls. Recently, several kinds of photonic or sonic crystals have been proposed as classical counterparts of valley-Hall topological insulators. However, direct experimental observation of valley-polarized edge states in photonic crystals is still difficult until now. Here, we demonstrate a designer surface plasmon crystal comprising metallic patterns deposited on a dielectric substrate, which can become a valley-Hall photonic topological insulator by exploiting the mirror-symmetry-breaking mechanism. Topological edge states with valley-dependent transport are directly visualized in the microwave regime. The observed edge states are confirmed to be fully valley-polarized through spatial Fourier transforms. Topological protection of the edge states at sharp corners is also experimentally demonstrated.

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Source: https://tomesphere.com/paper/1703.04570