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 (AMoS(2)NRs) 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.