Asymmetric Band Diagrams in Photonic Crystals with a Spontaneous Nonreciprocal Response

TL;DR

This paper investigates electromagnetic wave propagation in layered photonic crystals with nonreciprocal materials, revealing conditions for symmetric or asymmetric band diagrams and drawing analogies to biased ferrite responses.

Contribution

It proves that stratified Tellegen photonic crystals always have symmetric dispersion diagrams despite broken symmetries, and explores spectral asymmetry with combined chiral and nonreciprocal materials.

Findings

Stratified Tellegen photonic crystals have symmetric dispersion diagrams.

Combining chiral and nonreciprocal materials can produce spectral asymmetry.

Two-layer Tellegen media can mimic biased ferrite responses.

Abstract

We study the propagation of electromagnetic waves in layered photonic crystals formed by materials with a spontaneous nonreciprocal response, such as Tellegen (axion) media or topological insulators. Surprisingly, it is proven that stratified Tellegen photonic crystals that break simultaneously the space inversion and time reversal symmetries have always symmetric dispersion diagrams. Interestingly, we show that by combining chiral and nonreciprocal materials the photonic band diagrams can exhibit a spectral asymmetry such that . Furthermore, it is demonstrated that in some conditions two juxtaposed Tellegen medium layers have an electromagnetic response analogous to that of a biased ferrite slab.