Tuning band gaps in twisted bilayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Mo</mml:mi><mml:msub><mml:mi mathvariant="normal">S</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>
Yipei Zhang, Zhen Zhan, F. Guinea, Jose Ángel Silva-Guillén, Shengjun Yuan
Abstract
In the emerging world of twisted bilayer structures, the possible configurations are limitless, which enables a rich landscape of electronic properties. In this paper, we focus on twisted bilayer transition metal dichalcogenides (TMDCs) and study their properties by means of an accurate tight-binding model. We build structures with different angles and find that the so-called flat bands emerge when the twist angle is sufficiently tiny (smaller than $7.{3}^{\ensuremath{\circ}}$). Interestingly, the band gap can be tuned up to 5% (107 meV) when the twist angle in the relaxed sample varies from $21.{8}^{\ensuremath{\circ}}$ to ${0}^{\ensuremath{\circ}}$. Furthermore, when looking at the 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 TMDC-based optoelectronic devices.