Spectral imaging of topological edge states in plasmonic waveguide arrays

TL;DR

This paper demonstrates the experimental observation of topologically protected edge states in plasmonic waveguide arrays implementing the Su-Schrieffer-Heeger model, confirming their localization and spectral properties.

Contribution

It provides the first direct experimental evidence of topological edge states in plasmonic waveguide arrays using real-space and momentum-resolved imaging.

Findings

Edge states are localized at the interface between topologically distinct domains.

The edge states are confined to one sublattice, confirming topological protection.

The momentum spectrum shows the midgap position of the edge state.

Abstract

We report on the observation of a topologically protected edge state at the interface between two topologically distinct domains of the Su-Schrieffer-Heeger model, which we implement in arrays of evanescently coupled dielectric-loaded surface plasmon polariton waveguides. Direct evidence of the topological character of the edge state is obtained through several independent experiments: Its spatial localization at the interface as well as the restriction to one sublattice is confirmed by real-space leakage radiation microscopy. The corresponding momentum-resolved spectrum obtained by Fourier imaging reveals the midgap position of the edge state as predicted by theory.