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

The propagator of the induced dynamically screened Coulomb interaction W^{ind} (Q,\omega ,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 \epsilon _{eff} (\omega) of atomically thick crystals. It is shown that \epsilon _{eff } (\omega) 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 \epsilon\parallel (\omega) and perpendicular \epsilon\perp (\omega) dielectric functions in MoS_2 , which are compared with some previous measurements and calculations.

Vito Despoja, Zoran Rukelj, and Leonardo Marušić

DOI: 10.1103/PhysRevB.94.165446