Plasmonic topological edge states in ring-structure gate graphene.

Topological photonic states exhibit unique robustness against defects, facilitating fault-tolerant photonic device applications. However, existing proposals either involve a sophisticated and bulky structure or can only operate in the microwave regime. We show a theoretical demonstration for highly confined topologically protected plasmonic states to be realized at infrared frequencies in monolayer graphene with a ring-structure gate. With a suitable bias voltage, the combined gate-graphene structure is shown to produce sufficiently strong Bragg scattering of graphene surface plasmons and to impart them with nontrivial topological properties. Our design is compact and could pave the way for dynamically reconfigurable, robust, nanoscale, integrated photonic devices.