The Coulomb interaction in monolayer transition-metal dichalcogenides

TL;DR

This paper introduces a new Coulomb potential model for monolayer transition-metal dichalcogenides that accurately predicts exciton and trion binding energies and their environmental dependence, addressing limitations of previous models.

Contribution

The authors derive a novel potential considering the atomic structure of monolayers, improving agreement with experimental data on exciton and trion energies and environment effects.

Findings

New potential supports non-hydrogenic exciton Rydberg series.

Accurately predicts weak environmental dependence of trion binding energies.

Identifies trion-lattice coupling effects due to phonons.

Abstract

Recently, the celebrated Keldysh potential has been widely used to describe the Coulomb interaction of few-body complexes in monolayer transition-metal dichalcogenides. Using this potential to model charged excitons (trions), one finds a strong dependence of the binding energy on whether the monolayer is suspended in air, supported on SiO$_2$, or encapsulated in hexagonal boron-nitride. However, empirical values of the trion binding energies show weak dependence on the monolayer configuration. This deficiency indicates that the description of the Coulomb potential is still lacking in this important class of materials. We address this problem and derive a new potential form, which takes into account the three atomic sheets that compose a monolayer of transition-metal dichalcogenides. The new potential self-consistently supports (i) the non-hydrogenic Rydberg series of neutral excitons, and (ii) the weak dependence of the trion binding energy on the environment. Furthermore, we identify an important trion-lattice coupling due to the phonon cloud in the vicinity of charged complexes. Neutral excitons, on the other hand, have weaker coupling to the lattice due to the confluence of their charge neutrality and small Bohr radius.