Spontaneously Broken Particle-Hole Symmetry in Photonic Graphene with Gain and Loss

TL;DR

This paper investigates how balanced gain and loss in photonic graphene lead to spontaneously broken particle-hole symmetry, resulting in topologically protected edge states with purely imaginary eigenvalues that are robust against certain disorders.

Contribution

It introduces the concept of spontaneously broken particle-hole symmetry protecting edge states in photonic graphene with gain and loss, a novel topological phenomenon.

Findings

Edge states with purely imaginary eigenvalues appear along zigzag edges.

These edge states are protected by spontaneously broken particle-hole symmetry.

Protection is robust against certain disorders but can be lost under strong disorder.

Abstract

We consider particle-hole symmetric photonic graphene with balanced gain and loss. We show that edge states with purely imaginary eigenvalues appear along the zigzag edge. We propose an idea that these edge states are protected by spontaneously broken particle-hole symmetry. We discuss that the edge states are topological in the sense that the exceptional rings are robust against symmetry protecting disorder. If the disorder is too strong to restore the spontaneously broken particle-hole symmetry, then such protection of the edge states is lost.