Topological edge plasmons in graphene's viscous Hall fluid*

Graphene's viscous hall fluid is the first candidate for a non-local topological electromagnetic phase of matter. Here, the gap closes due to the viscous edge plasmons. This 2D topological viscous Hall insulator is characterized by an optical N invariant fundamentally different from the Chern insulator and quantum spin Hall insulator. It can support a unidirectional topological edge mode that is stable under various boundary conditions with different slip lengths and immune to back-scattering at edge defects. Here, we propose an ultra-subwavelength topological circulator (three-port non-reciprocal device) for THz region based on the unidirectional edge mode. The behavior of the circulator is studied by simulating a time-dependent linearized Navier-Stokes equation describing hall viscosity in fluid coupled to the electromagnetic field. We demonstrate the circulation behaviour of topological edge modes and the difference from traditional magnetoplasmons. Our work opens practical applications of graphene's viscous Hall fluid and simultaneously provides an experimental platform for studying topological hydrodynamics of light.