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

Hongyuan Li; Shaowei Li; Mit H Naik; Jingxu Xie; Xinyu Li; Jiayin Wang; Emma Regan; Danqing Wang; Wenyu Zhao; Sihan Zhao; Salman Kahn; Kentaro Yumigeta; Mark Blei; Takashi Taniguchi; Kenji Watanabe; Sefaattin Tongay; Alex Zettl; Steven G Louie; Feng Wang; Michael F Crommie

doi:10.1038/s41563-021-00923-6

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

Nat Mater. 2021 Jul;20(7):945-950. doi: 10.1038/s41563-021-00923-6. Epub 2021 Feb 8.

Authors

Hongyuan Li^#^{1

2

3}, Shaowei Li^#^{4

5

6}, Mit H Naik^#^{1

3}, Jingxu Xie¹, Xinyu Li¹, Jiayin Wang¹, Emma Regan^{1

2

3}, Danqing Wang^{1

2}, Wenyu Zhao¹, Sihan Zhao¹, Salman Kahn^{1

3}, Kentaro Yumigeta⁷, Mark Blei⁷, Takashi Taniguchi⁸, Kenji Watanabe⁹, Sefaattin Tongay⁷, Alex Zettl^{1

3

10}, Steven G Louie^{11

12}, Feng Wang^{13

14

15}, Michael F Crommie^{16

17

18}

Affiliations

¹ Department of Physics, University of California at Berkeley, Berkeley, CA, USA.
² Graduate Group in Applied Science and Technology, University of California at Berkeley, Berkeley, CA, USA.
³ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
⁴ Department of Physics, University of California at Berkeley, Berkeley, CA, USA. [email protected].
⁵ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
⁶ Kavli Energy Nano Sciences Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
⁷ School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA.
⁸ International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan.
⁹ Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan.
¹⁰ Kavli Energy Nano Sciences Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
¹¹ Department of Physics, University of California at Berkeley, Berkeley, CA, USA. [email protected].
¹² Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹³ Department of Physics, University of California at Berkeley, Berkeley, CA, USA. [email protected].
¹⁴ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹⁵ Kavli Energy Nano Sciences Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹⁶ Department of Physics, University of California at Berkeley, Berkeley, CA, USA. [email protected].
¹⁷ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹⁸ Kavli Energy Nano Sciences Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].

^# Contributed equally.

PMID: 33558718
DOI: 10.1038/s41563-021-00923-6

Abstract

Moiré superlattices in transition metal dichalcogenide (TMD) heterostructures can host novel correlated quantum phenomena due to the interplay of narrow moiré flat bands and strong, long-range Coulomb interactions^1-9. However, microscopic knowledge of the atomically reconstructed moiré superlattice and resulting flat bands is still lacking, which is critical for fundamental understanding and control of the correlated moiré phenomena. Here we quantitatively study the moiré flat bands in three-dimensional (3D) reconstructed WSe₂/WS₂ moiré superlattices by comparing scanning tunnelling spectroscopy (STS) of high-quality exfoliated TMD heterostructure devices with ab initio simulations of TMD moiré superlattices. A strong 3D buckling reconstruction accompanied by large in-plane strain redistribution is identified in our WSe₂/WS₂ moiré heterostructures. STS imaging demonstrates that this results in a remarkably narrow and highly localized K-point moiré flat band at the valence band edge of the heterostructure. A series of moiré flat bands are observed at different energies that exhibit varying degrees of localization. Our observations contradict previous simplified theoretical models but agree quantitatively with ab initio simulations that fully capture the 3D structural reconstruction. Our results reveal that the strain redistribution and 3D buckling in TMD heterostructures dominate the effective moiré potential and the corresponding moiré flat bands at the Brillouin zone K points.

Abstract

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