Excitonic fingerprint of atomically thin 2D materials

As atomically thin nanomaterials with a weak dielectric screening, monolayer transition metal dichalcogenides (TMDs) show a remarkably strong Coulomb interaction giving rise to the formation of tightly bound excitons. In addition to the optically accessible bright excitonic states, there is also a variety of optically forbidden states including excitons exhibiting a non-zero angular momentum or center-of-mass momentum.

Here, a review of our recent research on these 2D materials is presented. We study the excitonic fingerprint in optical absorption and differential transmission spectra based on a microscopic approach that combines the Wannier equation with TMD Bloch equations. We show the appearance of a pronounced Rydberg-like series of excitonic transitions with binding energies in the range of 0.5 eV. We investigate the microscopic origin of their homogeneous linewidth including radiative and phonon-assisted non-radiative relaxation channels. We reveal a significant disorder-induced coupling of bright and dark excitons offering a strategy to circumvent optical selection rules and make dark states visible in optical spectra. We predict a novel sensor mechanism for molecules based on dark excitonic states. Finally, we study the exciton valley dynamics including Coulomb-driven intervalley coupling processes.