Electronic structure, magnetoexcitons and valley polarized electron gas in 2D crystals

TL;DR

This paper explores the electronic, optical, and magnetic properties of 2D materials like MoS2 and WS2, focusing on magnetoexcitons, valley polarization, and the effects of magnetic fields on their electronic structures.

Contribution

It presents a detailed analysis of the Landau level structure, valley Zeeman splitting, and magneto-exciton spectrum in monolayer MoS2, including electron-electron interactions and optical signatures.

Findings

Landau levels and valley Zeeman splitting characterized

Electron-electron interactions influence magneto-exciton spectrum

Valley-polarized electron gas in WS2 shows distinct optical features

Abstract

We describe here recent work on the electronic properties, magnetoexcitons and valley polarised electron gas in 2D crystals. Among 2D crystals, monolayer $MoS_2$ has attracted significant attention as a direct-gap 2D semiconductor analogue of graphene. The crystal structure of monolayer $MoS_2$ breaks inversion symmetry and results in K valley selection rules allowing to address individual valleys optically. Additionally, the band nesting near Q points is responsible for enhancing the optical response of $MoS_2$.We show that at low energies the electronic structure of $MoS_2$ is well approximated by the massive Dirac Fermion model. We focus on the effect of magnetic field on optical properties of $MoS_2$. We discuss the Landau level structure of massive Dirac fermions in the two non-equivalent valleys and resulting valley Zeeman splitting. The effects of electron-electron interaction on the valley Zeeman splitting and on the magneto-exciton spectrum are described. We show the changes in the absorption spectrum as the self-energy, electron-hole exchange and correlation effects are included. Finally, we describe the valley-polarised electron gas in $WS_2$ and its optical signature in finite magnetic fields.