Robust Edge States in Amorphous Gyromagnetic Photonic Lattices

TL;DR

This study demonstrates that amorphous gyromagnetic photonic lattices can support topologically protected edge states and robust nonreciprocal transmission, even without long-range order, by leveraging short-range order.

Contribution

It reveals that topological photonic states persist in amorphous structures with only short-range order, expanding the understanding of topological phases beyond crystalline materials.

Findings

Topological gaps persist with sufficient short-range order.

Edge states propagate ballistically along the lattice edge.

Enhanced nonreciprocal transmission occurs even without spectral gaps.

Abstract

We numerically study amorphous analogues of a two-dimensional photonic Chern insulator. The amorphous lattices consist of gyromagnetic rods that break time-reversal symmetry, with the lattice sites generated by a close-packing algorithm. The level of short-range order is adjustable, and there is no long-range order. The topologically nontrivial gaps of the photonic Chern insulator are found to persist into the amorphous regime, so long as there is sufficient short-range order. Strongly nonreciprocal robust transmission occurs via edge states, which are shown to propagate ballistically despite the absence of long-range order, and to be exponentially localized along the lattice edge. Interestingly, there is an enhancement of nonreciprocal transmission even at very low levels of short-range order, where there are no discernable spectral gaps.