Many-body and spin-orbit effects on direct-indirect band gap transition of strained monolayer MoS$_2$ and WS$_2$

TL;DR

This study investigates how many-body interactions, spin-orbit coupling, and strain influence the electronic band structure of monolayer MoS$_2$ and WS$_2$, revealing the precise strain levels where direct-indirect band gap transitions occur.

Contribution

It provides a comprehensive analysis including multiple corrections to DFT, accurately determining the strain-induced direct-indirect band gap transition points in MoS$_2$ and WS$_2$.

Findings

Transition occurs at 2.7% strain in MoS$_2$

Transition occurs at 3.9% strain in WS$_2$

All many-body and spin-orbit effects significantly impact band gap calculations.

Abstract

Monolayer transition metal dichalcogenides are promising materials for photoelectronic devices. Among them, molybdenum disulphide (MoS$_2$) and tungsten disulphide (WS$_2$) are some of the best candidates due to their favorable band gap values and band edge alignments. Here we consider various perturbative corrections to the DFT electronic structure, e.g. GW, spin-orbit coupling, as well as many-body excitonic and trionic effects, and calculate accurate band gaps as a function of homogeneous strain in these materials. We show that all of these corrections are of comparable magnitudes and need to be included in order to obtain an accurate electronic structure. We calculate the strain at which the direct-to-indirect gap transition occurs. After considering all contributions, the direct to indirect gap transition strain is found to be at 2.7% in MoS$_2$ and 3.9% in WS$_2$. These values are generally higher than the previously reported theoretical values.