Influence of atomic relaxations on the moiré flat band wavefunctions in antiparallel twisted bilayer WS${}_{\text{2}}$

Abstract

Twisting bilayers of transition metal dichalcogenides (TMDs) gives rise to a periodic moiré potential resulting in flat electronic bands with localized wavefunctions and enhanced correlation effects. In this work, scanning tunneling microscopy is used to image a WS${}_2$ bilayer twisted approximately $3^{\circ }$ off the antiparallel alignment. Scanning tunneling spectroscopy reveals the presence of localized electronic states in the vicinity of the valence band onset. In particular, the onset of the valence band is observed to occur first in regions with a Bernal stacking in which S atoms are located on top of each other. In contrast, density-functional theory calculations on twisted bilayers which have been relaxed in vacuum predict the highest lying flat valence band to be localized in regions of AA' stacking. However, agreement with the experiment is recovered when the calculations are carried out on bilayers in which the atomic displacements from the unrelaxed positions have been reduced reflecting the influence of the substrate and finite temperature. This demonstrates the delicate interplay of atomic relaxations and the electronic structure of twisted bilayer materials.

21 pages, 7 figures

References in corpus (4)

• Lattice reconstruction induced multiple ultra-flat bands in twisted bilayer WSe2
• Rotational and Dilational Reconstruction in Transition Metal Dichalcogenide Moiré Bilayers
• Flatbands and Mechanical Deformation Effects in the Moiré Superlattice of MoS${}_2$-WSe${}_2$ Heterobilayers
• Flattening van der Waals heterostructure interfaces by local thermal treatment

Cited by in corpus (3)

• Review: Advanced characterization of the spatial variation of moiré heterostructures and moiré excitons
• Strong atomic reconstruction in twisted bilayers of highly flexible InSe: Machine-Learned Interatomic Potential and continuum model approaches
• Enhanced second-harmonic generation from WS${}_2$/ReSe${}_2$ heterostructure