Engineering Polaritons in Van Der Waals Heterostructures

Abstract

Atomically thick materials (with weak van der Waals interaction between the adjacent layers in a bulk state) and heterostructures assembled from such materials in varying combinations have attracted considerable interest due to their novel optical and electrical properties. Polaritons formed due to coupling of electromagnetic radiation and a dipole mode (optical phonons, plasmons, excitons) in such van der Waals heterostructures have myriad novel optical properties which lead to promising applications in sensing, light trafficking, and sub-diffraction focusing. Engineering the wavefronts and confinement of polaritons in such heterostructures is the first step in truly realizing such devices and their applications in nanophotonics. However, current methods are limited in manipulating the polariton propagation behavior. Moreover, achieving full-control of propagation of polaritons using on-demand reconfigurable nano-structures is elusive. In this thesis, we demonstrate a range of techniques by which polariton propagation can be manipulated. Finally, we demonstrate a method by which an arbitrary control of polariton propagation in a truly reconfigurable fashion can be achieved. We employ near field microscopy techniques to study the near fields of the guided polariton modes. These results provide new insights on the behavior of polaritons in vdW heterostructures and, while illustrating a general method, they open up possibilities for various applications including novel nanophotonic devices for transformation optics, a new way to characterize optical anisotropy in thin films, and designing heterostructures with extreme light confinement and tailored optical properties.