Photonic Floquet skin-topological effect

TL;DR

This paper introduces and experimentally demonstrates a new non-Hermitian skin-topological effect in photonics, arising from Floquet-driven nonreciprocal flow of topological edge states, revealing complex interactions between non-Hermiticity and topology.

Contribution

It presents the first experimental realization of the Floquet skin-topological effect, combining non-Hermitian skin effect with Floquet topological photonic lattices, and introduces a topological switch mechanism.

Findings

Non-Hermitian skin effect can be induced by pure loss in periodically driven systems.

All one-way edge states are localized at specific corners, showing skin-topological behavior.

A topological switch for the skin-topological effect is demonstrated via gap-closing.

Abstract

Non-Hermitian skin effect and photonic topological edge states are of great interest in non-Hermitian physics and optics. However, the interplay between them is largly unexplored. Here, we propose and demonstrate experimentally the non-Hermitian skin effect that constructed from the nonreciprocal flow of Floquet topological edge states, which can be dubbed 'Floquet skin-topological effect'. We first show the non-Hermitian skin effect can be induced by pure loss when the one-dimensional (1D) system is periodically driven. Next, based on a two-dimensional (2D) Floquet topological photonic lattice with structured loss, we investigate the interaction between the non-Hermiticity and the topological edge states. We observe that all the one-way edge states are imposed onto specific corners, featuring both the non-Hermitian skin effect and topological edge states. Furthermore, a topological switch for the skin-topological effect is presented by utilizing the gap-closing mechanism. Our experiment paves the way of realizing non-Hermitian topological effects in nonlinear and quantum regimes.