Topological photonic alloy

TL;DR

This paper introduces photonic alloys as non-periodic topological materials that sustain non-reciprocal edge states even at low concentrations of magnetic components, expanding the understanding of disordered topological photonics.

Contribution

It demonstrates the realization of photonic alloys with non-trivial topology in a non-periodic 2D system and characterizes their edge states through reflection phase winding.

Findings

Photonic alloys sustain chiral edge states at low magnetic rod concentrations.

Threshold concentrations for topological behavior approach zero in the thermodynamic limit for substitutional alloys.

Edge states persist despite local time-reversal symmetry breaking.

Abstract

We present the new concept of photonic alloy as a non-periodic topological material. By mixing non-magnetized and magnetized rods in a non-periodic 2D photonic crystal configuration, we realized photonic alloys in the microwave regime. Our experimental findings reveal that the photonic alloy sustains non-reciprocal chiral edge states (CESs) even at very low concentration of magnetized rods. The non-trivial topology and the associated edge states of these non-periodic systems can be characterized by the winding of the reflection phase. Our results indicate that the threshold concentrations for the investigated system within the first non-trivial band gap to exhibit topological behavior approach zero in the thermodynamic limit for substitutional alloys, while the threshold remains non-zero for interstitial alloys. At low concentration, the system exhibits an inhomogeneous structure characterized by isolated patches of non-percolating magnetic domains that are spaced far apart within a topologically trivial photonic crystal. Surprisingly, the system manifests CESs despite a local breakdown of time-reversal symmetry rather than a global one. Photonic alloys represent a new category of disordered topological materials, offering exciting opportunities for exploring topological materials with adjustable gaps.