Dramatic n-Type Doping of Monolayer Graphene with Ferroelectric LiNbO₃Crystals and Bilayer Two-Dimensional Electron Gases

Depolarization of spontaneous polarization of ferroelectric oxides can result in the formation of two-dimensional electron gas with high enough density to support visible surface plasmon polaritons (SPPs). Since the charge carriers accumulated mainly reside within a nanometer scale on the surface, it is easily affected by an external covering layer, such as monolayer graphene. In this work, we report the remarkable charge transfer from a well-known ferroelectric lithium niobate (LiNbO₃, LN) to a neighboring monolayer graphene and consequent striking effects. The optical properties of graphene-covered LN were investigated by monitoring the very first reflection (VFR), which is more expedient to realizing visible SPPs' excitation and resultant energy coupling, i.e., the VFR increase and greater dynamic range. This picture was further confirmed by the double-scattering portion from the composite LN slab and a striking valley in the transmission spectra. This work reveals the interactions between bilayer two-dimensional electronic systems, paving a way toward achieving tunable non-metallic plasmonic devices.