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 local discharge cascades for correlated electrons in WS2/WSe2 moiré superlattices

Nature Physics volume 17, pages 1114–1119 (2021)Cite this article

Subjects

Abstract

Transition metal dichalcogenide moiré heterostructures provide an ideal platform to explore the extended Hubbard model1, where long-range Coulomb interactions play a critical role in determining strongly correlated electron states. This has led to experimental observations of Mott insulator states at half filling2,3,4 as well as a variety of extended Wigner crystal states at different fractional fillings5,6,7,8,9. However, a microscopic understanding of these emerging quantum phases is still lacking. Here we describe a scanning tunnelling microscopy (STM) technique for the local sensing and manipulation of correlated electrons in a gated WS2/WSe2 moiré superlattice, which enables the experimental extraction of fundamental extended Hubbard model parameters. We demonstrate that the charge state of the local moiré sites can be imaged by their influence on the STM tunnelling current. In addition to imaging, we are also able to manipulate the charge state of correlated electrons. When we ramp the bias on the STM tip, there is a local discharge cascade of correlated electrons in the moiré superlattice, which allows us to estimate the nearest-neighbour Coulomb interaction. Two-dimensional mapping of the moiré electron charge states also enables us to determine the on-site energy fluctuations at different moiré sites. Our technique should be broadly applicable to many semiconductor moiré systems, offering a powerful tool for the microscopic characterization and control of strongly correlated states in moiré superlattices.

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: Local discharging of electrons at moiré sites by an STM tip.
Fig. 2: Discharging correlated electrons.
Fig. 3: Correlation effects on cascade discharging of moiré sites.
Fig. 4: Inhomogeneity of moiré on-site energy.

Similar content being viewed by others

Data availability

Source data are available for this paper at https://github.com/HongyuanLiCMP/Moire_discharging_STM_data. All other data that support the findings of this paper are available from the corresponding authors upon request.

References

  1. 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  ADS  Google Scholar 

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

    Article  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  6. Jin, C. et al. Stripe phases in WSe2/WS2 moiré superlattices. Nat. Mater. 20, 940–944 (2021).

    Article  ADS  Google Scholar 

  7. Xu, Y. et al. Correlated insulating states at fractional fillings of moiré superlattices. Nature 587, 214–218 (2020).

    Article  ADS  Google Scholar 

  8. Huang, X. et al. Correlated insulating states at fractional fillings of the WS2/WSe2 moiré lattice. Nat. Phys. 17, 715–719 (2021).

    Article  Google Scholar 

  9. Chu, Z. et al. Nanoscale conductivity imaging of correlated electronic states in WSe2/WS2 moiré superlattices. Phys. Rev. Lett. 125, 186803 (2020).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  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  ADS  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  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  18. Li, H. et al. Imaging moiré flat bands in three-dimensional reconstructed WSe2/WS2 superlattices. Nat. Mater. 20, 945–950 (2021).

    Article  ADS  Google Scholar 

  19. Zhang, C. et al. Probing critical point energies of transition metal dichalcogenides: surprising indirect gap of single layer WSe2. Nano Lett. 15, 6494–6500 (2015).

    Article  ADS  Google Scholar 

  20. Jung, S. et al. Evolution of microscopic localization in graphene in a magnetic field from scattering resonances to quantum dots. Nat. Phys. 7, 245–251 (2011).

    Article  Google Scholar 

  21. Pradhan, N. A., Liu, N., Silien, C. & Ho, W. Atomic scale conductance induced by single impurity charging. Phys. Rev. Lett. 94, 076801 (2005).

    Article  ADS  Google Scholar 

  22. Brar, V. W. et al. Gate-controlled ionization and screening of cobalt adatoms on a graphene surface. Nat. Phys. 7, 43–47 (2011).

    Article  Google Scholar 

  23. Wong, D. et al. Characterization and manipulation of individual defects in insulating hexagonal boron nitride using scanning tunnelling microscopy. Nat. Nanotechnol. 10, 949–953 (2015).

    Article  ADS  Google Scholar 

  24. Teichmann, K. et al. Controlled charge switching on a single donor with a scanning tunneling microscope. Phys. Rev. Lett. 101, 076103 (2008).

    Article  ADS  Google Scholar 

  25. Geick, R., Perry, C. & Rupprecht, G. Normal modes in hexagonal boron nitride. Phys. Rev. 146, 543–547 (1966).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

This work was funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under contract no. DE-AC02-05-CH11231 (van der Waals heterostructure programme KCFW16) (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), by the National Science Foundation award DMR-1926004 (structural determination) and by the National Science Foundation award DMR-1807233 (surface preparation). S.T. acknowledges support from DOE-SC0020653 (materials synthesis), Applied Materials Inc., NSF CMMI 1825594 (NMR and TEM studies), NSF DMR-1955889 (magnetic measurements), NSF CMMI-1933214, NSF 1904716, NSF 1935994, NSF ECCS 2052527, DMR 2111812 and CMMI 2129412. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by MEXT, Japan, grant number JPMXP0112101001; JSPS KAKENHI grant number JP20H00354; and CREST (JPMJCR15F3), JST, for bulk hBN crystal growth and analysis. E.R. acknowledges support from the Department of Defense (DoD) through the National Defense Science and Engineering Graduate Fellowship (NDSEG) programme. S.L. acknowledges support from Kavli ENSI Heising-Simons Junior Fellowship. M.H.N. thanks S. Kundu and M. Jain for their implementation of non-collinear wave-function plotting in Siesta.

Author information

Author notes

  1. These authors contributed equally: Hongyuan Li, Shaowei Li.

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, Emma Regan, Danqing Wang, Wenyu Zhao, Alex Zettl, Steven G. Louie, Michael F. Crommie & Feng Wang

  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, Alex Zettl, Steven G. Louie, Michael F. Crommie & Feng Wang

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

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

  5. Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, CA, USA

    Shaowei Li

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

    Kentaro Yumigeta, Mark Blei & Sefaattin Tongay

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

    Takashi Taniguchi

  8. 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. Emma Regan
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Danqing Wang
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Wenyu Zhao
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. Kentaro Yumigeta
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. Mark Blei
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. Takashi Taniguchi
    View author publications

    You can also search for this author in PubMed Google Scholar

  12. Kenji Watanabe
    View author publications

    You can also search for this author in PubMed Google Scholar

  13. Sefaattin Tongay
    View author publications

    You can also search for this author in PubMed Google Scholar

  14. Alex Zettl
    View author publications

    You can also search for this author in PubMed Google Scholar

  15. Steven G. Louie
    View author publications

    You can also search for this author in PubMed Google Scholar

  16. Michael F. Crommie
    View author publications

    You can also search for this author in PubMed Google Scholar

  17. Feng Wang
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

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

Corresponding authors

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

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Physics thanks Kam Tuen Law 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

Supplementary Figs. 1–5 and Discussion.

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 local discharge cascades for correlated electrons in WS2/WSe2 moiré superlattices. Nat. Phys. 17, 1114–1119 (2021). https://doi.org/10.1038/s41567-021-01324-x

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41567-021-01324-x

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