Manipulating propagating graphene plasmons at near field by shaped graphene nano-vacancies

摘要

Surface plasmons in graphene have many promising properties, such as high confinement, low losses, and gatetunability. However, it is also the high confinement that makes them difficult to excite due to their large momentum mismatch with free-space mid-infrared light. We propose to use shaped graphene nano-vacancies to compensate for the momentum mismatch, revealing its high flexibility in graphene plasmon (GP) excitation and manipulation. We first examine the electromagnetic standing waves generated with a pair of straight vacancies, in order to verify the excitation of GPs and to illustrate their tunability with gate voltage. Plasmonic lenses are then designed to achieve the super-focusing of mid-infrared light and to generate plasmonic vortices in graphene. A ～ 0.0125λ_0 hotspot is generated, far below the optical diffraction limit, hence revealing the capability of light control at deep-subwavelength scale.