Surface susceptibility and conductivity of MoS2 and WSe2 monolayers: A first-principles and ellipsometry characterization

We employ a recent formulation for the optical properties of two-dimensional crystals from first principles [L. Matthes et al., New J. Phys. 16, 105007 (2014); L. Matthes et al., Phys. Rev. B 94, 205408 (2016)] to compute the surface susceptibility and surface conductivity of MoS 2 and WSe 2 monolayers [G. Jayaswal et al., Opt. Lett. 43, 703 (2018)]. As electron-hole interactions are known to be crucial for the description of the absorption spectrum of monolayer transition metal dichalcogenides, the excitonic dielectric function is computed at the Bethe-Salpeter equation level, including spin-orbit interactions. For both of these examples, excellent agreement with experimental ellipsometry measurements is obtained. Driven by the emergence of additional features in our theoretical results, we applied a second-derivative analysis in order to identify excited exciton peaks in the ellipsometric spectra.