Twist induced inter-layer charge build up in a WS2 bilayer revealed by electron Compton scattering and density functional theory [dataset]

Exotic properties emerge from the electronic structure of few-layer transition metal dichalcogenides (TMDs), such as direct band gaps in monolayers and moiré excitons in twisted bilayers, which are exploited in modern optoelectronic devices and twistronics. Here Compton scattering in a transmission electron microscope (TEM) is used to probe the nature of the inter-layer electronic coupling in the TMD material WS2. The high spatial resolution and strong scattering in the TEM enables a complete analysis of individual WS2 domains, including their crystal structure. Compton measurements show that the electrons in an 18o twisted bilayer are more localized than in a monolayer. Density functional theory (DFT) simulations reveal this is caused by a twist induced charge build up in the inter-layer region, directly shielding the energetically unfavorable overlapping tungsten atoms. This unexpected result uncovers the precise role of twist angle on inter-layer coupling, and therefore the physical properties that depend on it.