Tuning band gaps in twisted bilayer MoS$_2$

TL;DR

This study investigates how twisting bilayer MoS2 affects its electronic properties, revealing tunable band gaps, flatbands at small angles, and electric field-induced phase transitions, aiding optoelectronic device design.

Contribution

It provides an accurate tight-binding model for twisted bilayer MoS2 and demonstrates how twist angle and electric fields can tune electronic properties.

Findings

Flatbands emerge at small twist angles (~7.3°).

Band gap varies up to 2.2% with twist angle changes.

Electric field induces semiconductor-metal transition.

Abstract

In the emerging world of twisted bilayer structures, the possible configurations are limitless, which enables for a rich landscape of electronic properties. In this paper, we focus on twisted bilayer transition metal dichalcogenides (TMDCs) and study its properties by means of an accurate tight-binding model. We build structures with different angles and find that the so-called flatbands emerge when the twist angle is sufficiently small (around 7.3$^{\circ}$). Interestingly, the band gap can be tuned up to a 2.2\% (51 meV) when the twist angle in the relaxed sample varies from 21.8$^{\circ}$ to 0.8$^{\circ}$. Furthermore, when looking at local density of states we find that the band gap varies locally along the moir\`e pattern due to the change in the coupling between layers at different sites. Finally, we also find that the system can suffer a transition from a semiconductor to a metal when a sufficiently strong electric field is applied. Our study can serve as a guide for the practical engineering of the TMDCs based optoelectronic devices.