Monolayers*

We revisit the excitonic spectrum in monolayer MoS₂ and how, in comparison with a single-particle picture, it strongly restructures the optical absorption spectrum over a large range of energies. Our expedited approach takes into account the anomalous screening in 2D and the presence of a substrate by the effective Keldysh potential. By solving the Bethe-Salpeter equation with a Slater-Koster parameterization of the first-principles single particle bandstructure, we obtain quantitative accuracy in relation to existing measurements. Our results capture well the absolute magnitude of the experimental optical conductivity and we scrutinize the details of the so-called C resonant excitons that provide a large spectral weight well within the continuum. The contributions to the C-excitons arise not only from the vicinity of the Gamma point, but from a set of rather broad portions of the Brillouin zone, consistent with their resonant nature and with recent experiments^1-2. We also study the effect of the contributions of higher energy bands and spin-flipping terms in the Hamiltonian, on the main features of the experimental optical absorption.
[1] Nanoscale, 6, 13028 (2014)
[2] Phys. Rev. B 87, 201401 (2013)