The Impact of Twist Engineering on Valley Polarization in Transition Metal Dichalcogenide Heterobilayers

In a groundbreaking study published in Science Advances, researchers have delved into the world of twist engineering in electrically controlled transition metal dichalcogenide heterobilayers (hBLs). This study highlights the crucial role that the moiré period plays in the valley polarization switching and polarization degree of these heterobilayers.

Twist engineering emerges as a powerful tool in manipulating the valley degrees of freedom of interlayer excitons (IXs). By adjusting the twist angle between different monolayers, researchers have uncovered a novel method to control the excitonic potential, thus enhancing the controllability of valley properties in these heterostructures.

The researchers demonstrated that the valley polarization of IXs can be effectively controlled by tweaking the twist angle in fabricated WSe2/WS2 heterostructure devices. The degree of circular polarization (DCP) and polarization switching were found to be directly influenced by the moiré period determined through twist engineering.

Unraveling the intricate physical mechanisms behind twist angle dependent DCP, the researchers examined both intralayer and interlayer perspectives. A larger moiré period led to a lower interlayer excitonic potential at local minima, confining more excitons and enhancing DCP. On the other hand, a larger twist angle resulted in an increase in intralayer electron-hole (e-h) exchange interactions, leading to a reduction in intralayer valley lifetime and ultimately, a decrease in interlayer valley polarization.

Theoretical calculations based on first-principle theory shed light on the dependence of the excitonic potential difference on the moiré period. With the twist angle playing a pivotal role, the difference of the excitonic potential between two minima was found to increase, requiring a higher external bias for devices with a larger twist angle to switch the polarization.

Building upon the polarization switching mechanism, the researchers introduced a valley-addressable encoding device that serves as a stepping stone for future non-volatile memories. This innovative device showcases the potential of twist engineering in revolutionizing the field of valleytronic devices.

The study illuminates the transformative impact of twist engineering on valley polarization in transition metal dichalcogenide heterobilayers. By unraveling the intricate interplay between twist angle, moiré period, and excitonic potential, researchers have opened up new avenues for the development of advanced optoelectronic applications.

Science

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