Anomalous topological waves in strongly amorphous scattering networks

TL;DR

This paper demonstrates that in a two-dimensional amorphous scattering network, topological edge transport persists even under strong amorphism, challenging the conventional understanding that disorder destroys topological states.

Contribution

It introduces a new amorphous topological regime for electromagnetic waves that survives arbitrarily strong disorder, with experimental evidence of unidirectional edge transport in such systems.

Findings

Unidirectional edge transport persists in strongly amorphous networks.

Anomalous edge states are mediated by topological invariants.

Topological protection extends beyond crystalline structures.

Abstract

Topological insulators are crystalline materials that have revolutionized our ability to control wave transport. They provide us with unidirectional channels that are immune to obstacles, defects or local disorder, and can even survive some random deformations of their crystalline structures. However, they always break down when the level of disorder or amorphism gets too large, transitioning to a topologically trivial Anderson insulating phase. Here, we demonstrate a two-dimensional amorphous topological regime that survives arbitrarily strong levels of amorphism. We implement it for electromagnetic waves in a non-reciprocal scattering network and experimentally demonstrate the existence of unidirectional edge transport in the strong amorphous limit. This edge transport is shown to be mediated by an anomalous edge state whose topological origin is evidenced by direct topological invariant measurements. Our findings extend the reach of topological physics to a new class of systems in which strong amorphism can induce, enhance and guarantee the topological edge transport instead of impeding it.