Dynamically tunable directional subwavelength beam propagation based on photonic spin Hall effect in graphene-based hyperbolic metamaterials.

Photonic spin Hall effect (PSHE) of type II hyperbolic metamaterials is achieved due to near filed interference, which provides a way to decide the propagation direction of subwavelength beam. In this paper, we propose graphene-based hyperbolic metamaterials (GHMMs), which is composed of the alternating graphene/SiO2 multilayer. The numerical results show that when a dipole emitter is placed at the boundary of the GHMMs, the subwavelength beam with λ/40 full-with half maximum can be excited and propagates along the left or right channel, which is dependent on polarization handedness. In addition, we further demonstrate that the unidirectional propagation angle can be dynamically tuned by changing the external electric field bias applied to graphene.