Electrically induced tunable chirality in achiral graphene metasurfaces.

A method for spatially controlling the electronic charge transport properties of graphene is proposed via the use of a lateral electrostatic bias field. The method is shown via electrostatics simulations to produce considerable shifts in the graphene Fermi energy, which in-turn tunes the electrical conductivity. This mechanism is incorporated into a THz frequency metasurface design consisting of a patterned graphene unit-cell (a delta-shaped graphene patch) which exhibits one axis of symmetry. Upon application of the lateral electrostatic bias, the charge redistribution in the graphene spatially alters the electrical conductivity of the monolayer, thereby breaking the symmetry of the system and introducing chirality. The magnitude of the chirality increases with the magnitude of the lateral electrostatic bias, or can be reversed by changing the sign of the bias field. Further, the response can be removed by the removal of the bias field, thereby returning to a achiral system. In addition to enabling filtering and sensing of circularly polarized light, this lateral biasing strategy offers a general route for spatially controlling charge carrier properties in graphene and other two-dimensional materials.