Tuning Anderson localization of edge-mode graphene plasmons in randomly gated nanoribbons.

Abstract

Edge-mode graphene plasmons (EGPs) supported by graphene nanoribbons are highly confined, and they can show versatile tunability under electrostatic bias. In order to efficiently enhance and actively control the near-field intensity in integrated plasmonic devices, we theoretically study Anderson localization of EGPs in a graphene nanoribbon with an underlying electrode array in this work. By randomly arranging the electrodes in the array, positional disorder is introduced in the graphene nanoribbon system. Consequently, the Anderson localization of EGPs occurs with an exponentially decreased electric field, reduced propagation length, and rapid disappearance of the cross-correlation coefficient. Physically, inhomogeneous gating effectively creates a disordered distribution of Fermi levels in the graphene nanoribbon, which provides adequate fluctuation of the effective refractive index and results in strong localization of the EGPs at mid-infrared regime. By changing electrode array arrangements, the EGPs can be trapped at distinct locations in the nanoribbon. Further considering that the Fermi-level disorder can be introduced by randomly modulating the electrostatic bias, we apply different gate voltages at different electrodes in the array. Electrically tunable Anderson localization of EGPs are eventually realized in those randomly gated nanoribbons. Moreover, by combining both the positional and Fermi-level disorders in the system, the Anderson localization becomes more actively controlled in this electrically gated graphene nanoribbons. It is shown that the local field can be selectively trapped at single distinct location, or even several locations along the graphene nanoribbon. This investigation extends the Anderson localization to the EGPs in the mid-infrared range and enriches the graphene-based active plasmonic devices.