Topologically protected plasmon mode with ultrastrong field localization in a graphene-based metasurface.

Graphene plasmons, the electromagnetic waves coupled to charge excitations in a graphene sheet, have attracted great interest because of their intriguing properties, such as electrical tunability, long plasmon lifetime, and high degree of spatial confinement. They may enable the manufacture of novel optical devices with extremely high speed, low driving voltage, low power consumption and compact sizes. In this paper, we propose a graphene-based metasurface which can support a topologically protected graphene plasmon mode with the ability of ultrastrong field localization. We show that such a plasmonic metasurface, constructed by depositing a graphene sheet on a periodic silicon substrate, would exhibit different bandgap topological characteristics as the filling factor of the periodic substrate changes. By setting suitable Fermi levels of graphene at two different areas of the metasurface, topological interface plasmon modes can be excited, resulting in over 8 orders of magnitude enhancement of the plasmon intensity. The topologically protected plasmon mode is robust against the perturbation of the structural parameters, and its frequency can be tuned by adjusting the gate-voltage on the graphene sheet. This highly integrated platform could provide a pathway for low-power and actively controllable nonlinear optics.