Electron and light confinement in laterally structured graphene devices

The electron liquid is a model used to study the interactions among electrons in physical systems. An example is given by graphene, a two-dimensional (2D) material in which the electron liquid is formed by massless relativistic electrons. Because of this, graphene has widely been exploited to study exotic phenomena. For example, the transmission of carriers across potential barriers in graphene is influenced by Klein tunnelling, which reduces the backscattering. Consequently, electrons in graphene show ballistic behaviour over micrometric distances, thus making such systems perfect platforms to study quantum interference. Moreover, graphene can sustain plasmon polaritons (PPs), resulting from the coupling of electromagnetic waves with electronic oscillations in the crystal. PPs confine light in subwavelength volumes, yielding an increased energy density exploitable for light-matter interaction studies. In addition, graphene properties can be tuned by engineering structural defects in its lattice. Among the other effects, the engineered defects act as barriers reflecting PPs and create local potential barriers for carriers, employable to explore coherent phenomena usually studied in systems involving a more complex fabrication. In this work, we study the effects of the confinement of light and electrons on light-matter interaction and on coherent interference of ballistic carriers in laterally structured graphene systems. With a simulation campaign, we investigate light-matter interaction in a system in which PPs launched in graphene by an array of metallic features are coupled to the transition between quantized electrons inside a III-V quantum well (QW), reaching strong coupling even in the few-electron regime. We optimize the fabrication of the array and study the optical response of one of the simulated systems, observing signatures of weak coupling between the excitations. Furthermore, we investigate the properties of defects induced in graphene with electron beam irradiation at 20 keV. We focus on the impact of a regular array of defected lines on the transport properties of graphene channels. We observe regular oscillations in the resistance curve of graphene as a macroscopic effect of the quantum coherent interference of the carriers in the channel. Our systems are prototypical platforms to efficiently study strong coupling involving few electrons and collective effects in the electron liquid of graphene.