Imaging moiré flat bands in three-dimensional reconstructed WSe₂/WS₂ superlattices

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• Moiré superlattices in transition metal dichalcogenide (TMD) heterostructures exhibit novel correlated quantum phenomena.
• Understanding the atomic reconstruction and flat bands is crucial for controlling these phenomena.

Purpose of the Study:

• To quantitatively study moiré flat bands in 3D reconstructed WSe2/WS2 moiré superlattices.
• To link structural reconstructions to the properties of moiré flat bands.

Main Methods:

• Scanning tunnelling spectroscopy (STS) on high-quality exfoliated TMD heterostructures.
• Ab initio simulations of TMD moiré superlattices.
• Comparison of experimental STS data with theoretical simulations.

Main Results:

• Identified strong 3D buckling reconstruction and significant in-plane strain redistribution in WSe2/WS2 moiré heterostructures.
• Observed a narrow, highly localized K-point moiré flat band at the valence band edge.
• Detected multiple moiré flat bands with varying localization at different energies.

Conclusions:

• 3D buckling and strain redistribution in TMD heterostructures significantly influence the effective moiré potential.
• The observed moiré flat bands, particularly at Brillouin zone K points, are dominated by these structural effects.
• Results challenge simplified models and highlight the importance of 3D reconstruction for understanding correlated moiré phenomena.