Investigation of indirect excitons in bulk 2H-MoS2 using transmission electron energy-loss spectroscopy

We have investigated indirect excitons in bulk 2H-MoS2 using transmission electron energy-loss spectroscopy. The electron energy-loss spectra were measured for various momentum transfer values parallel to the Gamma K and Gamma M directions of the Brillouin zone. The results allowed the identification of the indirect excitons between the valence band K-v and conduction band Lambda(c) points, the Gamma(v) and K-c points as well as adjacent K-v and <stack>K-c(')</stack>; points. The energy-momentum dispersions for the K-v-Lambda(c), Gamma(v)-K-c and K-v1-<stack>K-c(')</stack>; excitons along the Gamma K line are presented. The former two transitions exhibit a quadratic dispersion which allowed calculating their effective exciton masses based on the effective mass approximation. The K-v1-<stack>K-c(')</stack> transition follows a more linear dispersion relationship.