Graphene plasmon cavities

Abstract

In the past decades, we have witnessed the rapid growth of plasmonics, which is a field investigating the properties and applications of surface plasmon polaritons. Two key features of plasmons are that they enable us overcome the diffraction limit and they provide large field enhancement on the surface of metals. However, traditional surface plasmon polaritons have some significant drawbacks, such as high loss and low tunability. Fortunately, new materials with plasmon-like behaviour, such as graphene and silicon carbide, have recently been found both theoretically and experimentally. Compared to traditional plasmonic materials, those new materials exhibit low loss and high tunability and work at mid-infrared frequencies, significantly expanding this field. However, the coupling between different plasmon-like behaviours in those new materials has been largely unsuccessful to date. In this thesis, we investigate the coupling between the localized surface phonon polaritons of silicon carbide and surface plasmon polaritons of graphene, by studying the tunable plasmonic cavities working at the mid-infrared frequencies, using a monolayer of graphene deposited on a silicon carbide grating. Models for graphene plasmonic cavities are established to reveal the underlying physics. We first focus on a simple model by considering a Fabry-Perot model in the horizontal cavity direction, in which the commonly used dispersion relation of graphene plasmons is applied. Then, we improve the model by deriving a new dispersion relation, revealing the cavity height dependence of the dispersion relation of graphene plasmons. A Fabry-Perot model in the vertical cavity direction is also established. Last, we establish the model of the suspended graphene plasmon cavities based on the newly derived relationship. In addition, we realize several interesting features by optimizing the proposed system, such as complete absorption, extremely high field enhancement and extraordinary field compression. All these models are confirmed by the numerical simulations.