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Bilayer WSe2 as a natural platform for interlayer exciton condensates in the strong coupling limit

Nature Nanotechnology volume 17, pages 577–582 (2022)Cite this article

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Abstract

Exciton condensates (ECs) are macroscopic coherent states arising from condensation of electron–hole pairs1. Bilayer heterostructures, consisting of two-dimensional electron and hole layers separated by a tunnel barrier, provide a versatile platform to realize and study ECs2,3,4. The tunnel barrier suppresses recombination, yielding long-lived excitons5,6,7,8,9,10. However, this separation also reduces interlayer Coulomb interactions, limiting the exciton binding strength. Here, we report the observation of ECs in naturally occurring 2H-stacked bilayer WSe2. In this system, the intrinsic spin–valley structure suppresses interlayer tunnelling even when the separation is reduced to the atomic limit, providing access to a previously unattainable regime of strong interlayer coupling. Using capacitance spectroscopy, we investigate magneto-ECs, formed when partially filled Landau levels couple between the layers. We find that the strong-coupling ECs show dramatically different behaviour compared with previous reports, including an unanticipated variation of EC robustness with the orbital number, and find evidence for a transition between two types of low-energy charged excitations. Our results provide a demonstration of tuning EC properties by varying the constituent single-particle wavefunctions.

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Fig. 1: Independent layer population in bilayer WSe2.
Fig. 2: EC formation and gap opening at LL crossings.
Fig. 3: Conditions for EC formation.
Fig. 4: Different types of charged excitations for different LLs.

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Data availability

Experimental data relevant to figures in the main text and data of numerical calculations are available at https://doi.org/10.5281/zenodo.6377084. All other raw data are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank E. Tutuc for helpful discussions and W. Coniglio and B. Pullum for help with experiments at the National High Magnetic Field Lab. This research is primarily supported by the US Department of Energy (DE-SC0016703). Synthesis of WSe2 (D.R., B.K., K.B.) was supported by the Columbia University Materials Science and Engineering Research Center, through National Science Foundation grants DMR-1420634 and DMR-2011738. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation cooperative agreement no. DMR-1157490 and the State of Florida. D.A.A. acknowledges support by the Swiss National Science Foundation and by the European Research Council (grant agreement no. 864597). Z.P. acknowledges support by the Leverhulme Trust Research Leadership Award RL-2019-015. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the Ministry of Education, Culture, Sports, Science and Technology, Japan (grant no. JPMXP0112101001) and Japan Society for the Promotion of Science KAKENHI (grant nos JP19H05790 and JP20H00354).

Author information

Author notes

  1. En-Min Shih

    Present address: Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA

  2. En-Min Shih

    Present address: Department of Physics, Georgetown University, Washington, DC, USA

Authors and Affiliations

  1. Department of Physics, Columbia University, New York, NY, USA

    Qianhui Shi, En-Min Shih & Cory R. Dean

  2. Department of Physics and Astronomy, University of California, Los Angeles, CA, USA

    Qianhui Shi

  3. Department of Mechanical Engineering, Columbia University, New York, NY, USA

    Daniel Rhodes, Bumho Kim & James Hone

  4. Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USA

    Katayun Barmak

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

    Kenji Watanabe

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

    Takashi Taniguchi

  7. School of Physics and Astronomy, University of Leeds, Leeds, UK

    Zlatko Papić

  8. Department of Theoretical Physics, University of Geneva, Geneva, Switzerland

    Dmitry A. Abanin

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Contributions

Q.S. fabricated the devices, performed the capacitance measurements and analysed the data. E.-M.S. fabricated devices and performed transport measurements that complement the capacitance data. Z.P. and D.A.A. provided theoretical input and performed the numerical calculations. D.R. and B.K. grew the WSe2 crystals under the supervision of J.H. and K.B.; K.W. and T.T. grew the hexagonal boron nitride crystals. Q.S., C.R.D., J.H., Z.P. and D.A.A. wrote the manuscript with input from all authors.

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Correspondence to Cory R. Dean.

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Nature Nanotechnology thanks Liang Fu and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Shi, Q., Shih, EM., Rhodes, D. et al. Bilayer WSe2 as a natural platform for interlayer exciton condensates in the strong coupling limit. Nat. Nanotechnol. 17, 577–582 (2022). https://doi.org/10.1038/s41565-022-01104-5

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