Charged Excitons In Two-Dimensional Transition Metal Dichalcogenides: Semiclassical Calculation Of Berry Curvature Effects

We theoretically study the role of the Berry curvature on neutral and charged excitons in two-dimensional transition metal dichalcogenides. The Berry curvature arises due to a strong coupling between the conduction and valence bands in these materials that can to great extent be described within the model of massive Dirac fermions. The Berry curvature lifts the degeneracy of exciton states with opposite angular momentum. Using an electronic interaction that accounts for nonlocal screening effects, we find a Berry-curvature induced splitting of similar to 17 meV between the 2p(-) and 2p(+) exciton states in WS2. Furthermore, we calculate the trion binding energies in WS2 and WSe2 for a large variety of screening lengths and different dielectric constants for the environment. Our approach indicates the prominent role played by the Berry curvature along with nonlocal electronic interactions in the understanding of the energy spectra of neutral and charged excitons in transition metal dichalcogenides and in the interpretation of their optical properties.