Ab initio study of electronic excitations and the dielectric function in molybdenum disulfide monolayer

摘要

The propagator of the induced dynamically screened Coulomb interaction W~(ind)(Q,ω,z,z') is calculated for the MoS_2 monolayer. The energy-loss rate of a point charge placed near the MoS_2 monolayer is calculated (using the spatial resolution of the W~(ind) in the direction perpendicular to the MoS_2 plane) and successfully compared with very recent electron-energy-loss spectroscopy measurements of Hong et al. [J. Hong et al., Phys. Rev. B 93, 075440 (2016)]. The induced propagator W~(ind), compared with its classical analogous propagator, is used to determine the effective dielectric function ∈_(eff)(ω) of atomically thick crystals. It is shown that ∈_(eff)(ω) extracted from W~(ind) is in good agreement with the dielectric function of the MoS_2 extracted from the ellipsometry measurements. A recently proposed method for calculation of the dielectric tensor in quasi-two-dimensional crystals is used to calculate the parallel ∈_‖(ω) and perpendicular ∈_⊥(ω) dielectric functions in MoS_2, which are compared with some previous measurements and calculations.