Band nesting and exciton spectrum in monolayer MoS$_2$

TL;DR

This paper investigates how band nesting and topology influence the exciton spectrum in monolayer MoS$_2$ by solving the Bethe-Salpeter equation with an ab initio tight-binding model, revealing detailed exciton states and the effects of band structure features.

Contribution

It provides a comprehensive ab initio analysis of exciton states in MoS$_2$, including the effects of band nesting, topology, and Coulomb interactions, advancing understanding beyond simplified models.

Findings

Identification of conduction-valence band nesting and Q minima in MoS$_2$

Accurate calculation of ground and excited exciton states

Analysis of contributions from band structure and Coulomb interactions

Abstract

We discuss here the effect of band nesting and topology on the spectrum of excitons in a single layer of MoS$_2$, a prototype transition metal dichalcogenide material. We solve for the single particle states using the ab initio based tight-binding model containing metal $d$ and sulfur $p$ orbitals. The metal orbitals contribution evolving from $K$ to $\Gamma$ points results in conduction-valence band nesting and a set of second minima at $Q$ points in the conduction band. There are three $Q$ minima for each $K$ valley. We accurately solve the Bethe-Salpeter equation including both $K$ and $Q$ points and obtain ground and excited exciton states. We determine the effects of the electron-hole single particle energies including band nesting, direct and exchange screened Coulomb electron-hole interactions and resulting topological magnetic moments on the exciton spectrum. The ability to control different contributions combined with accurate calculations of the ground and excited exciton states allows for the determination of the importance of different contributions and a comparison with effective mass and $k\cdot p$ massive Dirac fermion models.