Fig. 3. Ab initio results and model for plasmon dispersion relation of monolayer TaS₂.

a A real quasi-2D metal can be formulated as: a 2D electron gas with renormalized properties given by the energy band (or bands) that crosses the Fermi energy (thick band in Fig. 1a) embedded in an environment with an effective screening, which accounts for the interband transitions and environmental effects (Eq. (1) and Fig. 1c). b Calculated plasmon dispersion relation of monolayer TaS₂ on a variety of substrates (Polytetrafluoroethylene (PTFE), BN, WSe₂)–calculated from first principles (solid colored lines) and computed with the expression given in Eq. (1) (dash colored lines). For the latter, we fit the ab initio computed intrinsic effective dielectric screening ε_eff(q) of suspended TaS₂ to the form of a Keldysh model²¹. The resulting curves of the model on different substrates are then obtained without any additional fitting. The Landau damping regions are also shown (gray shaded regions), which is associated with the electron-hole continuum of either intraband or interband transitions (Fig. 1a).