Microscopic Modeling of Exciton-Polaritons in Two-Dimensional Materials

Sammanfattning: Integrating 2D materials into high-quality optical microcavities opens the door to fascinating many-particle phenomena including the formation of exciton-polaritons. These are hybrid quasi-particles inheriting properties of both the constituent photons and excitons. The corresponding change in the dispersion relation has a large impact on the optics, dynamics and transport behaviour of the materials. In this thesis, we aim to microscopically understand the optical response and propagation of exciton-polaritons in transition metal dichalcogenides (TMDs). The theoretical method is based on the density matrix formalism combined with the Hopfield approach. In particular, we investigate how the diffusion of exciton changes in the strong coupling regime, i.e. when exciton-polaritons are formed. Furthermore, we study the impact of dark excitons on the optical response of upper and lower polariton branches in absorption spectra of molybdenum- and tungsten-based TMDs, which are known to be direct and indirect semiconductors, respectively. Furthermore, we show how different experimentally accessible quantities, such as temperature or mirror reflectance, can be exploited to tune the optical response of polaritons. Our study contributes to an improved microscopic understanding of exciton-polaritons and their interaction with phonons, potentially suggesting experiments that could determine the energy of dark exciton states via momentum-resolved polariton absorption.