Active Valley-topological Plasmonic Crystal in Metagate-tuned Graphene

A valley plasmonic crystal using graphene surface plasmons is proposed. We design a metagate to induce periodic doping on the graphene such that the local fermi energy on grephene spatially varies in a triangular pattern with broken mirror symmetry. Under the mirror symmetry breaking, the system supports plasmonic bandgaps that host topological valley-selective edge modes at domain walls, and the suppressed inter-valley scattering enables reflection-free transport of these edge plasmons along sharply curved pathways. This valley-based approach enables non-magnetic and purely electronic schemes for reconfigurable topological plasmonic devices, and a possible design involving two metagates---topgate and backgate---can be used for a dynamical control over topological valley transport of infrared plasmons.