Excitonic structure of the optical conductivity in MoS2 monolayers

We investigate the excitonic spectrum of ${\mathrm{MoS}}₂$ monolayers and calculate its optical absorption properties over a wide range of energies. Our approach takes into account the anomalous screening in two dimensions and the presence of a substrate, both cast by a suitable effective Keldysh potential. We solve the Bethe-Salpeter equation using as a basis a Slater-Koster tight-binding model parameterized to fit the ab initio ${\mathrm{MoS}}₂$ band structure calculations. The resulting optical conductivity is in good quantitative agreement with existing measurements up to ultraviolet energies. We establish that the electronic contributions to the $C$ excitons arise not from states at the $\mathrm{\ensuremath{\Gamma}}$ point, but from a set of $\mathbit{k}$ points over extended portions of the Brillouin zone. Our results reinforce the advantages of approaches based on effective models to expeditiously explore the properties and tunability of excitons in TMD systems.