Optical non-Hermitian skin effect in uniform media

Non-Hermitian skin effect (NHSE), which is a localization phenomenon in non-Hermitian systems, has recently been of great interest. Most previous works in various systems studied periodic systems. However, electromagnetic waves do not feel the periodicity of a system if the wavelength is sufficiently long, and it has not been clear that electromagnetic waves exhibit the localization caused by the non-Hermiticity itself even in uniform systems without the periodicity. Here, we establish the theory of the optical NHSE in non-Hermitian uniform media and show that the optical NHSE occurs even in uniform media. We apply our theory to subwavelength metamaterials and demonstrate the existence of a non-Hermitian skin mode in a multilayer metamaterial. Finally, we propose a concept of a stationarily excited skin mode to describe a lossy system under stationary excitation with real excitation frequency.