Highly-Controllable Plasmon-Phonon Polaritons in Nonlinear-Graphene-LiF Waveguides

The combination of polar dielectrics with graphene plasmonics has opened a new research area due to its fascinating properties. This paper aims to study the propagating characteristics of a new nano-structure, constituting graphene-LiF-Nonlinear layers in the far-infrared frequencies. An analytical model for the proposed heterostructure is presented, embarking on Maxwell's equations, deriving a wave equation for each layer, and then applying the boundary conditions at the borders. In this article, a complicated dispersion relation is derived for the proposed structure. The analytical results declare that a high value of the figure of merit (FOM), i.e. FOM = 24.5, is obtained at the frequency of 9.22 THz. Furthermore, it will be shown that the propagating features of our heterostructure for Hybrid Surface Plasmon Phonon Polaritons (HSP3) in three regions, i.e. inside, below, and above the Reststrahlen band, is effectively tuned by the chemical potential and the nonlinear coefficient. Our proposed structure can be a promising candidate for multi-functional applications such as waveguides, absorbers, and sensors in the THz region.