Probing topological protection using a designer surface plasmon structure

TL;DR

This paper demonstrates the creation and testing of topological photonic edge states in a designer surface plasmon platform, revealing their robustness and the existence of anomalous Floquet topological states beyond traditional invariants.

Contribution

It introduces a novel plasmonic platform for topological photonics and experimentally probes the robustness of topological edge states against various defects, including anomalous Floquet states.

Findings

Topological edge states are constructed in a plasmonic platform.

Robustness of these states is tested against defects, including some that break protection.

First experimental realization of anomalous Floquet topological edge states.

Abstract

Topological photonic states, inspired by robust chiral edge states in topological insulators, have recently been demonstrated in a few photonic systems, including an array of coupled on-chip ring resonators at communication wavelengths. However, the intrinsic difference between electrons and photons determines that the topological protection in time-reversal-invariant photonic systems does not share the same robustness as its counterpart in electronic topological insulators. Here, in a designer surface plasmon platform consisting of tunable metallic sub-wavelength structures, we construct photonic topological edge states and probe their robustness against a variety of defect classes, including some common time-reversal-invariant photonic defects that can break the topological protection, but do not exist in electronic topological insulators. This is also the first experimental realization of anomalous Floquet topological edge states, whose topological phase cannot be predicted by the usual Chern number topological invariants.