Optically and Chemically Controllable Light Flow in Topological Plasmonic Waveguides Based on Graphene Metasurfaces

In this work, topologically-protected plasmon transport is demonstrated in graphene-based plasmonic crystal waveguides, the main ideas being subsequently applied to optically and chemically controllable nanodevices. In two configurations of topological graphene metasurfaces created by breaking their inversion symmetry, symmetry-protected Dirac cones associated to the underlying metasurfaces are gapped out, which leads to the formation of topological valley modes inside the nontrivial bandgap. The propagation of the corresponding topological modes shows unidirectional characteristics in both cases. Based on the proposed plasmonic topological waveguides, an active optical nanoswitch and a gas molecular sensor are designed by optically and chemically tuning the frequency dispersion of graphene metasurfaces via Kerr effect and gas molecular absorption, respectively. Specifically, the variation of the frequency dispersion of graphene can switch the topological mode into the region of leaky bulk modes, resulting in a dramatic variation of the plasmon transmission. Our work may contribute to the development of new ultracompact and ultrafast active photonic nanodevices based on graphene.