Theory of intervalley Coulomb interactions in monolayer transition-metal dichalcogenides

TL;DR

This paper develops a theoretical framework to understand intervalley Coulomb interactions in monolayer transition-metal dichalcogenides, explaining new optical features observed under high electron densities through many-body effects.

Contribution

It introduces a dynamical Coulomb potential model and calculates electron self-energy, revealing correlation-induced virtual states that explain experimental luminescence phenomena.

Findings

Identification of a correlation-induced virtual state in the band-gap.

Explanation of luminescence in monolayer WSe2 and WS2 under high electron density.

Moderate redshift of electron energy levels due to exchange interactions.

Abstract

Exciton optical transitions in transition-metal dichalcogenides offer unique opportunities to study rich many-body physics. Recent experiments in monolayer WSe$_2$ and WS$_2$ have shown that while the low-temperature photoluminescence from neutral excitons and three-body complexes is suppressed in the presence of elevated electron densities or strong photoexcitation, new dominant peaks emerge in the low-energy side of the spectrum. I present a theory that elucidates the nature of these optical transitions showing the role of the intervalley Coulomb interaction. After deriving a compact dynamical form for the Coulomb potential, I calculate the self-energy of electrons due to their interaction with this potential. For electrons in the upper valleys of the spin-split conduction band, the self energy includes a moderate redshift due to exchange, and most importantly, a correlation-induced virtual state in the band-gap. The latter sheds light on the origin of the luminescence in monolayer WSe$_2$ and WS$_2$ in the presence of pronounced many-body interactions.