Topologically protected Dirac plasmons in graphene

TL;DR

This paper demonstrates theoretically that simple graphene structures under moderate magnetic fields can host topologically protected Dirac plasmons at infrared frequencies, enabling robust, nanoscale photonic devices.

Contribution

It introduces a straightforward method to realize topologically protected optical states in graphene at infrared frequencies using a magnetic field, avoiding complex designs.

Findings

Graphene plasmons exhibit nonreciprocal behavior at superlattice junctions.

Topologically protected edge states emerge in patterned graphene under magnetic fields.

The approach is applicable to other 2D materials for robust photonic applications.

Abstract

Topological optical states exhibit unique immunity to defects and the ability to propagate without losses rendering them ideal for photonic applications.A powerful class of such states is based on time-reversal symmetry breaking of the optical response.However, existing proposals either involve sophisticated and bulky structural designs or can only operate in the microwave regime. Here, we propose and provide a theoretical proof-of-principle demonstration for highly confined topologically protected optical states to be realized at infrared frequencies in a simple 2D material structure-a periodically patterned graphene monolayer-subject to a magnetic field below 1 tesla. In our graphene honeycomb superlattice structures plasmons exhibit substantial nonreciprocal behavior at the superlattice junctions, leading to the emergence of topologically protected edge states and localized bulk modes enabled by the strong magneto-optical response of this material, which leads to time-reversal-symmetry breaking already at moderate static magnetic fields. The proposed approach is simple and robust for realizing topologically nontrivial 2D optical states, not only in graphene, but also in other 2D atomic layers, and could pave the way for realizing fast, nanoscale, defect-immune devices for integrated photonics applications.