Strong Light-Matter Interactions in 2D Materials

Doktorsavhandling, 2026

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 exciton diffusion 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. We show how different experimentally accessible quantities, such as temperature or mirror reflectance, can be exploited to tune the optical response of polaritons. By changing the cavity detuning, we vary the polariton energy relative to the unaffected dark excitons in such a way that we open or close specific phonon-driven scattering channels. In a joint theory-experiment, with the group of Christian Schneider (University of Oldenburg), we show that this controlled switching of scattering channels manifests in characteristic sharp changes in the optical spectra of polaritons. These spectral features can be exploited to extract the position of dark excitons. This suggests new possibilities for exploiting polaritons for fingerprinting nanomaterials via their unique exciton landscape. Overall, this work contributed to a better microscopic understanding of optics, dynamics and transport of exciton-polaritons in technologically promising 2D materials.