Charged exctions in two-dimensional transition-metal dichalcogenides - semiclassical calculation of Berry-curvature effects

TL;DR

This paper investigates how Berry curvature influences exciton and trion energy spectra in two-dimensional transition-metal dichalcogenides, revealing significant energy splittings and the importance of electronic interactions.

Contribution

It provides a semiclassical calculation demonstrating Berry curvature effects on excitons and trions, aligning with experimental data and highlighting their role in optical properties.

Findings

Berry curvature causes ~17 meV splitting in exciton states.

Calculated trion binding energies vary with screening and dielectric environment.

Berry curvature and non-local interactions are crucial for understanding exciton spectra.

Abstract

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 non-local screening effects, we find a Berry-curvature induced splitting of $\sim 17$ meV between the 2$p_{-}$ and 2$p_{+}$ exciton states in WS$_2$, consistent with experimental findings. Furthermore, we calculate the trion binding energies in WS$_2$ and WSe$_2$ for a large variety of screening lenghts and different dielectric constants for the environment. Our approach indicates the prominent role played by the Berry curvature along with non-local electronic interactions in the understanding of the energy spectra of neutral and charged excitons in transition-metal dichalcogenides and in the the interpretation of their optical properties.