Electronic properties of single-layer and multilayer transition metal dichalcogenides $MX_2$ ($M=$ Mo, W and $X=$ S, Se)

TL;DR

This review discusses the electronic, optical, and superconducting properties of single- and multilayer transition metal dichalcogenides, emphasizing strain effects, disorder impacts, and excitonic phenomena based on density functional theory calculations.

Contribution

It provides a comprehensive overview of the electronic properties and tunability of $MX_2$ materials, integrating recent theoretical and experimental findings.

Findings

Band structures are highly sensitive to strain and can be engineered.

Disorder affects optical and transport properties significantly.

Superconductivity mechanisms in $MX_2$ are diverse and actively researched.

Abstract

Single- and few-layer transition metal dichalcogenides have recently emerged as a new family of layered crystals with great interest, not only from the fundamental point of view, but also because of their potential application in ultrathin devices. Here we review the electronic properties of semiconducting $MX_2$, where $M=$Mo or W and $X=$ S or Se. Based on of density functional theory calculations, which include the effect of spin-orbit interaction, we discuss the band structure of single-layer, bilayer and bulk compounds. The band structure of these compounds is highly sensitive to elastic deformations, and we review how strain engineering can be used to manipulate and tune the electronic and optical properties of those materials. We further discuss the effect of disorder and imperfections in the lattice structure and their effect on the optical and transport properties of $MX_2$. The superconducting transition in these compounds, which has been observed experimentally, is analyzed, as well as the different mechanisms proposed so far to explain the pairing. Finally, we include a discussion on the excitonic effects which are present in these systems.