Optical absorption of armchair MoS₂ nanoribbons: Enhanced correlation effects in the reduced dimension

We carry out first-principles calculations of the quasi-particle band structure and optical absorption spectra of H-passivated armchair MoS₂ nanoribbons (AMoS₂NRs) by employing the approach combining the Green's function perturbation theory (GW) and the Bethe-Salpeter equation (BSE), i.e., GW+BSE. Optical absorption spectra of AMoS₂NRs show the exciton multibands (their binding energies are close to or less than 1 eV) which are much stronger than a single layer of MoS₂. However, they are absent in the spectra by the approach of GW and the random phase approximation (RPA), i.e., GW+RPA. This signifies that the excitonic correlation effects are strongly enhanced in the reduced dimensional structure of MoS₂. We also calculate the exciton wave functions for the few lowest energy excitons, which are found to have non-Frenkel character.