Quantum Spin Hall Edge States and Interlayer Coupling in Twisted Bilayer WTe2

The quantum spin Hall (QSH) effect, characterized by topologically protected spin-polarized edge states, was recently demonstrated in monolayers of the transition metal dichalcogenide (TMD) WTe2. However, the robustness of this topological protection remains largely unexplored in van der Waals heterostructures containing one or more layers of a QSH insulator. In this work, we use scanning tunneling microscopy and spectroscopy (STM/STS) to explore the topological nature of twisted bilayer (tBL) WTe2. At the tBL edges, we observe the characteristic spectroscopic signatures of the QSH edge states. For small twist angles, a rectangular moire pattern develops, which results in local modifications of the band structure. Using first-principles calculations, we quantify the interactions in tBL WTe2 and its topological edge states as a function of interlayer distance and conclude that it is possible to engineer the topology of WTe2 bilayers via the twist angle as well as interlayer interactions.

Automated summary

In this study, the topological nature of twisted bilayer WTe2 was investigated using scanning tunneling microscopy and spectroscopy (STM/STS). The characteristic spectroscopic signatures of the quantum spin Hall edge states were observed at the edges of the twisted bilayer. Through calculations, it was found that the topology of WTe2 bilayers can be engineered by adjusting the twist angle and interlayer interactions.