Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

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

Nature Materials volume 20, pages 945–950 (2021)Cite this article

Subjects

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 interactions1,2,3,4,5,6,7,8,9. 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.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Aligned WSe2/WS2 heterostructure.
Fig. 2: Moiré superlattice reconstruction.
Fig. 3: STS measurement of moiré-induced flat bands.
Fig. 4: Ab initio calculations of the electronic structure in reconstructed moiré superlattice.

Similar content being viewed by others

Data availability

The data supporting the findings of this study are included in the main text and in the Supplementary Information files, and are also available at https://github.com/HongyuanLiCMP/Moire_STM_source_data.

References

  1. Tang, Y. et al. Simulation of Hubbard model physics in WSe2/WS2 moiré superlattices. Nature 579, 353–358 (2020).

    Article  CAS  Google Scholar 

  2. Wu, F., Lovorn, T., Tutuc, E. & MacDonald, A. H. Hubbard model physics in transition metal dichalcogenide moiré bands. Phys. Rev. Lett. 121, 026402 (2018).

    Article  CAS  Google Scholar 

  3. Shimazaki, Y. et al. Strongly correlated electrons and hybrid excitons in a moiré heterostructure. Nature 580, 472–477 (2020).

    Article  CAS  Google Scholar 

  4. Regan, E. C. et al. Mott and generalized Wigner crystal states in WSe2/WS2 moiré superlattices. Nature 579, 359–363 (2020).

    Article  CAS  Google Scholar 

  5. Wang, L. et al. Correlated electronic phases in twisted bilayer transition metal dichalcogenides. Nat. Mater. 19, 861–866 (2020).

    Article  CAS  Google Scholar 

  6. Yankowitz, M. et al. Tuning superconductivity in twisted bilayer graphene. Science 363, 1059–1064 (2019).

    Article  CAS  Google Scholar 

  7. Liu, X. et al. Tunable spin-polarized correlated states in twisted double bilayer graphene. Nature 583, 221–225 (2020).

    Article  CAS  Google Scholar 

  8. Kim, K. et al. Tunable moiré bands and strong correlations in small-twist-angle bilayer graphene. Proc. Natl Acad. Sci. USA 114, 3364–3369 (2017).

    Article  CAS  Google Scholar 

  9. Lu, X. et al. Superconductors, orbital magnets and correlated states in magic-angle bilayer graphene. Nature 574, 653–657 (2019).

    Article  CAS  Google Scholar 

  10. Cao, Y. et al. Correlated insulator behaviour at half-filling in magic-angle graphene superlattices. Nature 556, 80–84 (2018).

    Article  CAS  Google Scholar 

  11. Cao, Y. et al. Unconventional superconductivity in magic-angle graphene superlattices. Nature 556, 43–50 (2018).

    Article  CAS  Google Scholar 

  12. Zondiner, U. et al. Cascade of phase transitions and Dirac revivals in magic-angle graphene. Nature 582, 203–208 (2020).

    Article  CAS  Google Scholar 

  13. Burg, G. W. et al. Correlated insulating states in twisted double bilayer graphene. Phys. Rev. Lett. 123, 197702 (2019).

    Article  CAS  Google Scholar 

  14. Cao, Y. et al. Tunable correlated states and spin-polarized phases in twisted bilayer–bilayer graphene. Nature 583, 215–220 (2020).

    Article  CAS  Google Scholar 

  15. Chen, G. et al. Evidence of a gate-tunable Mott insulator in a trilayer graphene moiré superlattice. Nat. Phys. 15, 237–241 (2019).

    Article  CAS  Google Scholar 

  16. Chen, G. et al. Tunable correlated Chern insulator and ferromagnetism in a moiré superlattice. Nature 579, 56–61 (2020).

    Article  CAS  Google Scholar 

  17. Chen, G. et al. Signatures of tunable superconductivity in a trilayer graphene moiré superlattice. Nature 572, 215–219 (2019).

    Article  CAS  Google Scholar 

  18. Slagle, K. & Fu, L. Charge transfer excitations, pair density waves, and superconductivity in moiré materials. Phys. Rev. B 102, 235423 (2020).

    Article  CAS  Google Scholar 

  19. Zhang, Y., Yuan, N. F. & Fu, L. Moiré quantum chemistry: charge transfer in transition metal dichalcogenide superlattices. Phys. Rev. B 102, 201115 (2020).

    Article  CAS  Google Scholar 

  20. Kerelsky, A. et al. Maximized electron interactions at the magic angle in twisted bilayer graphene. Nature 572, 95–100 (2019).

    Article  CAS  Google Scholar 

  21. Xie, Y. et al. Spectroscopic signatures of many-body correlations in magic-angle twisted bilayer graphene. Nature 572, 101–105 (2019).

    Article  CAS  Google Scholar 

  22. Jiang, Y. et al. Charge order and broken rotational symmetry in magic-angle twisted bilayer graphene. Nature 573, 91–95 (2019).

    Article  CAS  Google Scholar 

  23. Choi, Y. et al. Electronic correlations in twisted bilayer graphene near the magic angle. Nat. Phys. 15, 1174–1180 (2019).

    Article  CAS  Google Scholar 

  24. Pan, Y. et al. Quantum-confined electronic states arising from the moiré pattern of MoS2–WSe2 heterobilayers. Nano Lett. 18, 1849–1855 (2018).

    Article  CAS  Google Scholar 

  25. Zhang, C. et al. Interlayer couplings, moiré patterns, and 2D electronic superlattices in MoS2/WSe2 hetero-bilayers. Sci. Adv. 3, e1601459 (2017).

    Article  Google Scholar 

  26. Zhang, Z. et al. Flat bands in twisted bilayer transition metal dichalcogenides. Nat. Phys. 16, 1093–1096 (2020).

    Article  CAS  Google Scholar 

  27. Raja, A. et al. Coulomb engineering of the bandgap and excitons in two-dimensional materials. Nat. Commun. 8, 15251 (2017).

    Article  Google Scholar 

  28. Wang, G. et al. Colloquium: excitons in atomically thin transition metal dichalcogenides. Rev. Mod. Phys. 90, 021001 (2018).

    Article  CAS  Google Scholar 

  29. Ugeda, M. M. et al. Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor. Nat. Mater. 13, 1091–1095 (2014).

    Article  CAS  Google Scholar 

  30. Waters, D. et al. Flat bands and mechanical deformation effects in the moiré superlattice of MoS2-WSe2 heterobilayers. ACS Nano 14, 7564–7573 (2020).

    Article  CAS  Google Scholar 

Download references

Acknowledgements

This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division of the US Department of Energy under the van der Waals heterostructure program (KCWF16), contract number DE-AC02-05CH11231 (device electrode preparation, STM spectroscopy, DFT calculations and theoretical analysis). Support was also provided by the US Army Research Office under MURI award W911NF-17-1-0312 (device layer transfer), and by the National Science Foundation Awards DMR-1807233 (surface preparation) and DMR-1926004 (GW calculations). S.T. acknowledges support from DOE-SC0020653, NSF DMR 1552220, DMR 1904716 and NSF CMMI 1933214 for WSe2 and WS2 bulk crystal growth and analysis. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, grant number JPMXP0112101001, JSPS KAKENHI grant number JP20H00354 and the CREST(JPMJCR15F3), JST for bulk hBN crystal growth and analysis. E.C.R. acknowledges support from the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program. S.L. acknowledges support from Kavli ENSI Heising Simons Junior Fellowship. M.H.N. thanks S. Kundu and M. Jain for their implementation of noncollinear wavefunction plotting in Siesta. Computational resources were provided by Cori at National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science of the US Department of Energy under contract no. DE-AC02-05CH11231, Stampede2 at the Texas Advanced Computing Center (TACC) through Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation under grant no. ACI-1053575 and Frontera at TACC, which is supported by the National Science Foundation under grant no. OAC-1818253.

Author information

Author notes

  1. These authors contributed equally: Hongyuan Li, Shaowei Li, Mit H. Naik.

Authors and Affiliations

  1. Department of Physics, University of California at Berkeley, Berkeley, CA, USA

    Hongyuan Li, Shaowei Li, Mit H. Naik, Jingxu Xie, Xinyu Li, Jiayin Wang, Emma Regan, Danqing Wang, Wenyu Zhao, Sihan Zhao, Salman Kahn, Alex Zettl, Steven G. Louie, Feng Wang & Michael F. Crommie

  2. Graduate Group in Applied Science and Technology, University of California at Berkeley, Berkeley, CA, USA

    Hongyuan Li, Emma Regan & Danqing Wang

  3. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    Hongyuan Li, Shaowei Li, Mit H. Naik, Emma Regan, Salman Kahn, Alex Zettl, Steven G. Louie, Feng Wang & Michael F. Crommie

  4. Kavli Energy Nano Sciences Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    Shaowei Li, Alex Zettl, Feng Wang & Michael F. Crommie

  5. School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA

    Kentaro Yumigeta, Mark Blei & Sefaattin Tongay

  6. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan

    Takashi Taniguchi

  7. Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan

    Kenji Watanabe

Authors
  1. Hongyuan Li
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Shaowei Li
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Mit H. Naik
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Jingxu Xie
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Xinyu Li
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Jiayin Wang
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Emma Regan
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Danqing Wang
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. Wenyu Zhao
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. Sihan Zhao
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. Salman Kahn
    View author publications

    You can also search for this author in PubMed Google Scholar

  12. Kentaro Yumigeta
    View author publications

    You can also search for this author in PubMed Google Scholar

  13. Mark Blei
    View author publications

    You can also search for this author in PubMed Google Scholar

  14. Takashi Taniguchi
    View author publications

    You can also search for this author in PubMed Google Scholar

  15. Kenji Watanabe
    View author publications

    You can also search for this author in PubMed Google Scholar

  16. Sefaattin Tongay
    View author publications

    You can also search for this author in PubMed Google Scholar

  17. Alex Zettl
    View author publications

    You can also search for this author in PubMed Google Scholar

  18. Steven G. Louie
    View author publications

    You can also search for this author in PubMed Google Scholar

  19. Feng Wang
    View author publications

    You can also search for this author in PubMed Google Scholar

  20. Michael F. Crommie
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

M.F.C., F.W. and S.L. conceived the project, and S.G.L. supervised the theoretical calculations. H.L. and S.L. performed the STM measurements, and M.H.N. carried out the DFT and GW calculations. H.L., J.X., X.L., J.W., W.Z., S.Z. and S.K. fabricated the heterostructure device. E.R. and D.W. performed the second harmonic generation measurements. K.Y., M.B. and S.T. grew WSe2 and WS2 crystals. K.W. and T.T. grew the hBN single crystal. All authors discussed the results and wrote the manuscript.

Corresponding authors

Correspondence to Shaowei Li, Steven G. Louie, Feng Wang or Michael F. Crommie.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Materials thanks Andrea Young and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Materials and Methods and Supplementary Figs. 1–13.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Li, H., Li, S., Naik, M.H. et al. Imaging moiré flat bands in three-dimensional reconstructed WSe2/WS2 superlattices. Nat. Mater. 20, 945–950 (2021). https://doi.org/10.1038/s41563-021-00923-6

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41563-021-00923-6

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing