Optical non-Hermitian skin effect in two-dimensional uniform media

TL;DR

This paper develops a theory demonstrating that the optical non-Hermitian skin effect can occur in uniform anisotropic media with gain and loss, expanding the understanding of NHSE beyond periodic systems and proposing practical platforms for observation.

Contribution

It introduces a general theory of optical NHSE in uniform media, highlighting the role of anisotropy and material loss, and proposes multilayer metamaterials as a new platform for experimental realization.

Findings

NHSE occurs in uniform anisotropic media with gain and loss.

Localization is governed by an effective gauge potential from dielectric anisotropy.

Stationarily-excited skin modes with real frequencies are observable.

Abstract

The non-Hermitian skin effect (NHSE) is a novel localization phenomenon in certain non-Hermitian systems with gain and/or loss. Most of previous works study the non-Hermitian skin effect in periodic systems. However, electromagnetic waves often propagate within uniform materials without periodic modulation, and it has not been clear whether the optical NHSE occurs in uniform media such as bulk materials and electromagnetic metamaterials. Here we establish the theory of the optical NHSE in non-Hermitian anisotropic media. We show that the NHSE occurs even in uniform media with appropriate anisotropy and material loss. The localization of non-Hermitian skin modes are completely determined by an effective gauge potential caused by the anisotropy of a dielectric tensor. On the basis of the theory, we propose subwavelength multilayer metamaterials as a novel platform for the optical NHSE. We also propose a new concept of stationarily-excited skin modes whose frequencies are forced to be real in non-Hermitian systems. We find that the NHSE occurs even under the condition that the frequency is forced to be real, which implies that the NHSE we propose is observable under stationary excitation. Our work presents a general theory of the NHSE in homogeneous systems, and pave the way to realize the optical NHSE in bulk materials and metamaterials.