Symmetry-Based Classification of Chern Phases in Honeycomb Photonic Crystals

TL;DR

This paper develops a symmetry-based framework to classify Chern topological phases in honeycomb photonic crystals with nonreciprocal couplings, identifying key conditions for topological bandgaps and guiding the design of photonic topological insulators.

Contribution

It introduces a comprehensive symmetry-based classification of Chern phases considering arbitrary nonreciprocal interactions in photonic graphene.

Findings

Nonreciprocal interactions alone do not induce topological phases.

A nontrivial p6m component in nonreciprocal fields is necessary for topological bandgaps.

Provides practical guidelines for engineering topological phases in photonic crystals.

Abstract

In this work, we develop a symmetry-based classification of Chern phases in honeycomb photonic crystals, considering arbitrary nonreciprocal couplings compatible with energy conservation. Our analysis focuses on crystals formed through nonreciprocal perturbations of photonic graphene. These perturbations, which can have arbitrary spatial variations, are generally described by scalar and vector fields. Using a tight-binding model, we consider the most general nonreciprocal interactions, including gyromagnetic, pseudo-Tellegen, and moving medium responses, and examine how the corresponding nonreciprocal fields influence the crystal's topology. Our findings reveal that nonreciprocal interactions alone are insufficient to induce a topologically nontrivial phase. Instead, a nontrivial p6m component in the nonreciprocal fields is required to open a bandgap and achieve a non-zero Chern number. These results provide a symmetry-based roadmap for engineering photonic topological phases via nonreciprocal perturbations of photonic graphene, offering practical guidelines for designing topological phases in graphene-like photonic crystals.