Valley resolved moiré superlattices on twisted WSe₂ bilayers

Moiré superlattices have emerged as a major frontier in tailoring novel 2D electronic and excitonic structures. One approach is to twist homobilayers (TBL) of transition metal dichalcogenide (TMDs). Two groups have reported the observation of moiré superlattices in TBL WSe2. One fundamental issue in TMD TBL is whether the observed electronic superlattices are originated from the interlayer coupling at Γ or K valleys ^[1-2]. Many theoretical and experimental findings suggest that the moiré flat bands come from Κ valleys. Recent studies, however, suggest that the flat bands belong to Γ valleys ^[3-4]. Here, we utilize the scanning tunneling microscopy/spectroscopy (STM/STS) to study moiré superlattices in naturally formed twisted bilayer WSe2 at various angles grown by MOCVD. By conducting spectroscopy measurements at different modes, including standard constant height dI/dV, variable Z dI/dV, and <!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>? κ (decay constant) measurements, we are able to distinguish the moiré states from Γ, Κ valleys. Our experimental results have important implications on moiré design of valleytronics using twisted TMDs.

[1] Z. Zhang et al. Nat. Phys (2020)

[2] E. Li et al. Nat. Commun (2021)

[3] D. Pei et al. Physical Review X (2022)

[4] M. Angeli, A. H. Macdonald. Proceedings of the National Academy of Sciences (2021)