Twist-induced interlayer charge buildup in a WS2 bilayer revealed by electron Compton scattering and density functional theory

Exotic properties emerge from the electronic structure of few-layer transition-metal dichalcogenides (TMDs), such as direct band gaps in monolayers and moir\'e 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 interlayer electronic coupling in the TMD material $\mathrm{W}{\mathrm{S}}₂$. The high spatial resolution and strong scattering in the TEM enables a complete analysis of individual $\mathrm{W}{\mathrm{S}}₂$ domains, including their crystal structure. Compton measurements show that the electrons in an ${18}^{\ensuremath{\circ}}$ twisted bilayer are more localized than in a monolayer. Density functional theory simulations reveal this is caused by a twist-induced charge buildup in the interlayer region, directly shielding the energetically unfavorable overlapping tungsten atoms. This unexpected result uncovers the precise role of twist angle on interlayer coupling, and therefore the physical properties that depend on it.