Non-trivial point-gap topology and non-Hermitian skin effect in photonic crystals

TL;DR

This paper demonstrates that two-dimensional non-Hermitian photonic crystals with lossy materials can exhibit non-trivial point gap topology, leading to the non-Hermitian skin effect, and highlights the relevance of such topologies in realistic photonic systems.

Contribution

It shows that non-trivial point gap topology and the resulting skin effect can occur in realistic photonic crystals made of lossy materials, extending beyond tight-binding models.

Findings

Non-Hermitian photonic crystals can exhibit topological winding in complex frequency bands.

Non-trivial point gap topology induces non-Hermitian skin effect in truncated crystals.

Reciprocity influences the properties of the point gap topology.

Abstract

We show that two-dimensional non-Hermitian photonic crystals made of lossy material can exhibit non-trivial point gap topology in terms of topological winding in its complex frequency band structure. Such crystals can be either made of lossy isotropic media which is reciprocal, or lossy magneto-optical media which is non-reciprocal. We discuss the effects of reciprocity on the properties of the point gap topology. We also show that such a non-trivial point gap topology leads to non-Hermitian skin effect when the photonic crystal is truncated. In contrast to most previous studies on point gap topology which used tight-binding models, our work indicates that such non-Hermitian topology can studied in photonic crystals, which represent a more realistic system that has technological significance.