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.

  • Article
  • Published:

Strongly correlated electrons and hybrid excitons in a moiré heterostructure

Nature volume 580, pages 472–477 (2020)Cite this article

Subjects

Abstract

Two-dimensional materials and their heterostructures constitute a promising platform to study correlated electronic states, as well as the many-body physics of excitons. Transport measurements on twisted graphene bilayers have revealed a plethora of intertwined electronic phases, including Mott insulators, strange metals and superconductors1,2,3,4,5. However, signatures of such strong electronic correlations in optical spectroscopy have hitherto remained unexplored. Here we present experiments showing how excitons that are dynamically screened by itinerant electrons to form exciton-polarons6,7 can be used as a spectroscopic tool to investigate interaction-induced incompressible states of electrons. We study a molybdenum diselenide/hexagonal boron nitride/molybdenum diselenide heterostructure that exhibits a long-period moiré superlattice, as evidenced by coherent hole-tunnelling-mediated avoided crossings of an intralayer exciton with three interlayer exciton resonances separated by about five millielectronvolts. For electron densities corresponding to half-filling of the lowest moiré subband, we observe strong layer pseudospin paramagnetism, demonstrated by an abrupt transfer of all the (roughly 1,500) electrons from one molybdenum diselenide layer to the other on application of a small perpendicular electric field. Remarkably, the electronic state at half-filling of each molybdenum diselenide layer is resilient towards charge redistribution by the applied electric field, demonstrating an incompressible Mott-like state of electrons. Our experiments demonstrate that optical spectroscopy provides a powerful tool for investigating strongly correlated electron physics in the bulk and paves the way for investigating Bose–Fermi mixtures of degenerate electrons and dipolar excitons.

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: Device structure and basic characterization.
Fig. 2: Electric field dependence of PL and differential reflectance at charge neutrality.
Fig. 3: Gate dependence of differential reflectance spectrum of MoSe2/hBN/MoSe2.
Fig. 4: Gate dependence of intralayer exciton resonance in the low-electron-density regime.
Fig. 5: Electric field dependence of differential reflectance spectrum in the low-electron-density regime.

Similar content being viewed by others

Data availability

The data that support the findings of this study are available in the ETH Research Collection (http://hdl.handle.net/20.500.11850/399579).

References

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

    ADS  CAS  PubMed  Google Scholar 

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

    ADS  CAS  PubMed  Google Scholar 

  3. Liu, X. et al. Spin-polarized correlated insulator and superconductor in twisted double bilayer graphene. Preprint at http://arxiv.org/abs/1903.08130 (2019).

  4. Sharpe, A. L. et al. Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene. Science 365, 605–608 (2019).

    ADS  CAS  PubMed  Google Scholar 

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

    ADS  CAS  PubMed  Google Scholar 

  6. Sidler, M. et al. Fermi polaron-polaritons in charge-tunable atomically thin semiconductors. Nat. Phys. 13, 255–261 (2017).

    CAS  Google Scholar 

  7. Efimkin, D. K. & MacDonald, A. H. Many-body theory of trion absorption features in two-dimensional semiconductors. Phys. Rev. B 95, 035417 (2017).

    ADS  Google Scholar 

  8. Yu, H., Liu, G.-B., Tang, J., Xu, X. & Yao, W. Moiré excitons: from programmable quantum emitter arrays to spin-orbit–coupled artificial lattices. Sci. Adv. 3, e1701696 (2017).

    ADS  PubMed  PubMed Central  Google Scholar 

  9. Wu, F., Lovorn, T. & MacDonald, A. Topological exciton bands in moiré heterojunctions. Phys. Rev. Lett. 118, 147401 (2017).

    ADS  PubMed  Google Scholar 

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

    ADS  CAS  PubMed  Google Scholar 

  11. Ruiz-Tijerina, D. A. & Fal’ko, V. I. Interlayer hybridization and moiré superlattice minibands for electrons and excitons in heterobilayers of transition-metal dichalcogenides. Phys. Rev. B 99, 125424 (2019).

    ADS  CAS  Google Scholar 

  12. Rivera, P. et al. Interlayer valley excitons in heterobilayers of transition metal dichalcogenides. Nat. Nanotechnol. 13, 1004–1015 (2018).

    ADS  CAS  PubMed  Google Scholar 

  13. Seyler, K. L. et al. Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers. Nature 567, 66–70 (2019).

    ADS  CAS  PubMed  Google Scholar 

  14. Tran, K. et al. Evidence for moiré excitons in van der Waals heterostructures. Nature 567, 71–75 (2019).

    ADS  CAS  PubMed  Google Scholar 

  15. Alexeev, E. M. et al. Resonantly hybridized excitons in moiré superlattices in van der Waals heterostructures. Nature 567, 81–86 (2019); correction 572, E8 (2019).

    ADS  CAS  PubMed  Google Scholar 

  16. Jin, C. et al. Observation of moiré excitons in WSe2/WS2 heterostructure superlattices. Nature 567, 76–80 (2019); correction 569, E7 (2019).

    ADS  CAS  PubMed  Google Scholar 

  17. Wang, Z. et al. Evidence of high-temperature exciton condensation in two-dimensional atomic double layers. Nature 574, 76–80 (2019).

    ADS  CAS  PubMed  Google Scholar 

  18. Gerber, I. C. et al. Interlayer excitons in bilayer MoS2 with strong oscillator strength up to room temperature. Phys. Rev. B 99, 035443 (2019).

    ADS  CAS  Google Scholar 

  19. Zheng, L., Ortalano, M. W. & Das Sarma, S. Exchange instabilities in semiconductor double-quantum-well systems. Phys. Rev. B 55, 4506–4515 (1997).

    ADS  CAS  Google Scholar 

  20. Ezawa, Z. F. Quantum Hall Effects: Field Theoretical Approach and Related Topics (World Scientific, 2000).

  21. Zhang, Y. et al. Direct observation of the transition from indirect to direct bandgap in atomically thin epitaxial MoSe2. Nat. Nanotechnol. 9, 111–115 (2014).

    ADS  CAS  PubMed  Google Scholar 

  22. Özçelik, V. O., Azadani, J. G., Yang, C., Koester, S. J. & Low, T. Band alignment of two-dimensional semiconductors for designing heterostructures with momentum space matching. Phys. Rev. B 94, 035125 (2016).

    ADS  Google Scholar 

  23. Xu, X., Yao, W., Xiao, D. & Heinz, T. F. Spin and pseudospins in layered transition metal dichalcogenides. Nat. Phys. 10, 343–350 (2014).

    CAS  Google Scholar 

  24. Back, P. et al. Giant paramagnetism-induced valley polarization of electrons in charge-tunable monolayer MoSe2. Phys. Rev. Lett. 118, 237404 (2017).

    ADS  PubMed  Google Scholar 

  25. Smoleński, T. et al. Interaction-induced Shubnikov–de Haas oscillations in optical conductivity of monolayer MoSe2. Phys. Rev. Lett. 123, 097403 (2019).

    ADS  PubMed  Google Scholar 

  26. Hanson, R., Kouwenhoven, L. P., Petta, J. R., Tarucha, S. & Vandersypen, L. M. K. Spins in few-electron quantum dots. Rev. Mod. Phys. 79, 1217–1265 (2007).

    ADS  CAS  Google Scholar 

  27. Eisenstein, J. P., Pfeiffer, L. N. & West, K. W. Compressibility of the two-dimensional electron gas: measurements of the zero-field exchange energy and fractional quantum Hall gap. Phys. Rev. B 50, 1760–1778 (1994).

    ADS  CAS  Google Scholar 

  28. Hunt, B. M. et al. Direct measurement of discrete valley and orbital quantum numbers in bilayer graphene. Nat. Commun. 8, 948 (2017).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  29. Imada, M., Fujimori, A. & Tokura, Y. Metal-insulator transitions. Rev. Mod. Phys. 70, 1039–1263 (1998).

    ADS  CAS  Google Scholar 

  30. Camjayi, A., Haule, K., Dobrosavljević, V. & Kotliar, G. Coulomb correlations and the Wigner–Mott transition. Nat. Phys. 4, 932–935 (2008).

    CAS  Google Scholar 

  31. Zarenia, M., Neilson, D. & Peeters, F. M. Inhomogeneous phases in coupled electron-hole bilayer graphene sheets: charge density waves and coupled Wigner crystals. Sci. Rep. 7, 11510 (2017).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  32. Ludwig, D., Floerchinger, S., Moroz, S. & Wetterich, C. Quantum phase transition in Bose–Fermi mixtures. Phys. Rev. A 84, 033629 (2011).

    ADS  Google Scholar 

  33. Laussy, F. P., Kavokin, A. V. & Shelykh, I. A. Exciton-polariton mediated superconductivity. Phys. Rev. Lett. 104, 106402 (2010).

    ADS  PubMed  Google Scholar 

  34. Wang, L. et al. One-dimensional electrical contact to a two-dimensional material. Science 342, 614–617 (2013).

    ADS  CAS  PubMed  Google Scholar 

  35. Kim, K. et al. van der Waals heterostructures with high accuracy rotational alignment. Nano Lett. 16, 1989–1995 (2016).

    ADS  CAS  PubMed  Google Scholar 

  36. Catellani, A., Posternak, M., Baldereschi, A. & Freeman, A. J. Bulk and surface electronic structure of hexagonal boron nitride. Phys. Rev. B 36, 6105–6111 (1987).

    ADS  CAS  Google Scholar 

  37. Laturia, A., Van de Put, M. L. & Vandenberghe, W. G. Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk. npj 2D Mater. Appl. 2, 6 (2018).

    Google Scholar 

  38. Larentis, S. et al. Large effective mass and interaction-enhanced Zeeman splitting of K-valley electrons in MoSe2. Phys. Rev. B 97, 201407 (2018).

    ADS  CAS  Google Scholar 

  39. Rytova, N. S. The screened potential of a point charge in a thin film. Moscow Univ. Phys. Bull. 22, 18–21 (1967).

    Google Scholar 

  40. Lu, C.-P., Li, G., Watanabe, K., Taniguchi, T. & Andrei, E. Y. MoS2: choice substrate for accessing and tuning the electronic properties of graphene. Phys. Rev. Lett. 113, 156804 (2014).

    ADS  PubMed  Google Scholar 

  41. He, K., Poole, C., Mak, K. F. & Shan, J. Experimental demonstration of continuous electronic structure tuning via strain in atomically thin MoS2. Nano Lett. 13, 2931–2936 (2013).

    ADS  CAS  PubMed  Google Scholar 

  42. Conley, H. J. et al. Bandgap engineering of strained monolayer and bilayer MoS2. Nano Lett. 13, 3626–3630 (2013).

    ADS  CAS  PubMed  Google Scholar 

  43. Zhu, C. R. et al. Strain tuning of optical emission energy and polarization in monolayer and bilayer MoS2. Phys. Rev. B 88, 121301 (2013).

    ADS  Google Scholar 

  44. Frisenda, R. et al. Biaxial strain tuning of the optical properties of single-layer transition metal dichalcogenides. npj 2D Mater. Appl. 1, 10 (2017).

    Google Scholar 

  45. Giannozzi, P. et al. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials. J. Phys. Condens. Matter 21, 395502 (2009).

    PubMed  Google Scholar 

  46. Dal Corso, A. Pseudopotentials periodic table: from H to Pu. Comput. Mater. Sci. 95, 337–350 (2014).

    CAS  Google Scholar 

  47. Rasmussen, F. A. & Thygesen, K. S. Computational 2D materials database: electronic structure of transition-metal dichalcogenides and oxides. J. Phys. Chem. C 119, 13169–13183 (2015).

    CAS  Google Scholar 

  48. Zollner, K., Faria, P. E. Jr & Fabian, J. Proximity exchange effects in MoSe2 and WSe2 heterostructures with CrI3: twist angle, layer, and gate dependence. Phys. Rev. B 100, 085128 (2019).

    ADS  CAS  Google Scholar 

Download references

Acknowledgements

We acknowledge discussions with E. Demler, R. Schmidt, T. Smolenski, A. Popert and P. Knüppel. This work was supported by the Swiss National Science Foundation (SNSF) under grant number 200021-178909/1 and the European Research Council (ERC) Advanced Investigator Grant (POLTDES). Y.S. acknowledges support from the Japan Society for the Promotion of Science (JSPS) overseas research fellowships. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by MEXT, Japan, A3 Foresight by JSPS and CREST (grant number JPMJCR15F3) and JST.

Author information

Author notes

  1. These authors contributed equally: Yuya Shimazaki, Ido Schwartz

Authors and Affiliations

  1. Institute for Quantum Electronics, ETH Zürich, Zurich, Switzerland

    Yuya Shimazaki, Ido Schwartz, Martin Kroner & Ataç Imamoğlu

  2. National Institute for Materials Science, Tsukuba, Japan

    Kenji Watanabe & Takashi Taniguchi

Authors
  1. Yuya Shimazaki
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Ido Schwartz
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Kenji Watanabe
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Takashi Taniguchi
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Martin Kroner
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Ataç Imamoğlu
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

Y.S. and I.S. carried out the measurements. Y.S. designed and fabricated the sample. M.K. helped to prepare the experimental setup. K.W. and T.T. grew the hBN crystal. Y.S. performed DFT calculation. Y.S., I.S. and A.I. wrote the manuscript. A.I. supervised the project.

Corresponding authors

Correspondence to Yuya Shimazaki or Ataç Imamoğlu.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature thanks Wang Yao 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.

Extended data figures and tables

Extended Data Fig. 1 Optical microscope image of the device.

The border of each flake is highlighted with dashed lines, and the material is indicated in the grey box with the corresponding colour. Gr, graphene.

Extended Data Fig. 2 Effect of twist angle and strain on moiré periodicity.

a, Plot of the relation between twist angle and strain difference which gives same moiré periodicity (λmoiré), shown for λmoiré from 20 to 30 nm. b, Strain difference dependence of moiré periodicity for a fixed twist angle of 0.8°.

Extended Data Fig. 3 Band structure of R-stacked MoSe2/hBN/MoSe2 heterostructure obtained from DFT calculation.

a–c, The side and top view of the supercell for \({{\rm{R}}}_{{\rm{h}}}^{{\rm{h}}}\) (a), \({{\rm{R}}}_{{\rm{h}}}^{{\rm{X}}}\) (b) and \({{\rm{R}}}_{{\rm{h}}}^{{\rm{M}}}\) (c) used for the calculation. d–f, The calculated band structure of R-stacked MoSe2/hBN/MoSe2 for \({{\rm{R}}}_{{\rm{h}}}^{{\rm{h}}}\) (d), \({{\rm{R}}}_{{\rm{h}}}^{{\rm{X}}}\) (e) and \({{\rm{R}}}_{{\rm{h}}}^{{\rm{M}}}\) (f) lattice displacement. The insets show the magnified plot of the valence bands around the γ point.

Extended Data Table 1 DFT calculation results for MoSe2/hBN/MoSe2
Full size table

Supplementary information

Supplementary Information

This file contains Supplementary Information sections 1–8 including Supplementary Figures 1–10.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Shimazaki, Y., Schwartz, I., Watanabe, K. et al. Strongly correlated electrons and hybrid excitons in a moiré heterostructure. Nature 580, 472–477 (2020). https://doi.org/10.1038/s41586-020-2191-2

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41586-020-2191-2

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

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