Chiral plasmons with twisted atomic bilayers

TL;DR

This paper derives solutions for chiral plasmons in twisted bilayer structures, revealing how interlayer quantum coupling influences their properties and enabling new metasurface designs with unique phase and spin characteristics.

Contribution

It provides the first full Maxwell solutions for chiral plasmons in twisted bilayers, linking interlayer coupling to chiral surface conductivities and phase relationships.

Findings

Twisted bilayers act as chiral metasurfaces with magnetic and electric conductivities.

Interlayer quantum coupling determines the existence and phase of chiral plasmons.

Unique phase relationships enable construction of the longitudinal spin of plasmons.

Abstract

Van der Waals heterostructures of atomically thin layers with rotational misalignments, such as twisted bilayer graphene, feature interesting structural moir\'e superlattices. Due to the quantum coupling between the twisted atomic layers, light-matter interaction is inherently chiral; as such, they provide a promising platform for chiral plasmons in the extreme nanoscale. However, while the interlayer quantum coupling can be significant, its influence on chiral plasmons still remains elusive. Here we present the general solutions from full Maxwell equations of chiral plasmons in twisted atomic bilayers, with the consideration of interlayer quantum coupling. We find twisted atomic bilayers have a direct correspondence to the chiral metasurface, which simultaneously possesses chiral and magnetic surface conductivities, besides the common electric surface conductivity. In other words, the interlayer quantum coupling in twisted van der Waals heterostructures may facilitate the construction of various (e.g., bi-anisotropic) atomically-thin metasurfaces. Moreover, the chiral surface conductivity, determined by the interlayer quantum coupling, determines the existence of chiral plasmons and leads to a unique phase relationship (i.e., +/-{\pi}/2 phase difference) between their TE and TM wave components. Importantly, such a unique phase relationship for chiral plasmons can be exploited to construct the missing longitudinal spin of plasmons, besides the common transverse spin of plasmons.