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Ultrafast exciton fluid flow in an atomically thin MoS2 semiconductor

Nature Nanotechnology volume 18, pages 1012–1019 (2023)Cite this article

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Abstract

Excitons (coupled electron–hole pairs) in semiconductors can form collective states that sometimes exhibit spectacular nonlinear properties. Here, we show experimental evidence of a collective state of short-lived excitons in a direct-bandgap, atomically thin MoS2 semiconductor whose propagation resembles that of a classical liquid as suggested by the nearly uniform photoluminescence through the MoS2 monolayer regardless of crystallographic defects and geometric constraints. The exciton fluid flows over ultralong distances (at least 60 μm) at a speed of ~1.8 × 107 m s−1 (~6% the speed of light). The collective phase emerges above a critical laser power, in the absence of free charges and below a critical temperature (usually Tc ≈ 150 K) approaching room temperature in hexagonal-boron-nitride-encapsulated devices. Our theoretical simulations suggest that momentum is conserved and local equilibrium is achieved among excitons; both these features are compatible with a fluid dynamics description of the exciton transport.

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Fig. 1: Anomalous exciton transport driven by an electrical backgate in an atomically thin MoS2 semiconductor.
Fig. 2: Long-range transport of excitons.
Fig. 3: Exciton fluid transport and phase diagram.
Fig. 4: Ultrafast exciton fluid flow.
Fig. 5: Nonlinear transport and energy blueshift of fluid excitons.

Data availability

All methods and data generated and/or analysed supporting the findings of this study are included in this paper and its Supplementary Information and are available from the corresponding authors upon reasonable request.

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Acknowledgements

Q.X. gratefully acknowledges funding support from National Natural Science Foundation of China (12250710126), strong support from the State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University Initiative Scientific Research Program and a start-up grant from Tsinghua University. M.B. gratefully acknowledges support from the Nanyang Technological University for an NAP-SUG grant. This research is supported by the Ministry of Education, Singapore, under its Research Centre of Excellence award to the Institute for Functional Intelligent Materials (I-FIM, project number EDUNC-33-18-279-V12). M.K. acknowledges that this material is based upon work supported by the Air Force Office of Scientific Research and the Office of Naval Research under award number FA8655-21-1-7021. This research is supported by the Ministry of Education, Singapore, under its Academic Research Fund Tier 2 (MOE-T2EP50122-0012) and Tier 3 (MOE2018-T3-1-005). X.L. gratefully acknowledges support from the National Natural Science Foundation of China (12104006), and the Center of Strong Laser and High Magnetic Field at Anhui University. K.W. and T.T. acknowledge support from the EMEXT Element Strategy Initiative to Form Core Research Center through grant number JPMXP0112101001 and the CREST(JPMJCR15F3), JST. A.G.d.Á gratefully acknowledges financial support from the Singapore Ministry of Education via AcRF Tier 3 Programme Geometrical Quantum Materials (MOE2018-T3-1-002) and from the Presidential Postdoctoral Fellowship programme of the Nanyang Technological University. We thank T. C. H. Liew, A. Álvarez Fernández, I. Bar-Joseph and F. Dubin for fruitful discussions and suggestions on this manuscript.

Author information

Author notes

  1. These authors contributed equally: Andrés Granados del Águila, Yi Ren Wong.

Authors and Affiliations

  1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore

    Andrés Granados del Águila, Yi Ren Wong, Indrajit Wadgaonkar, Antonio Fieramosca, Stefano Dal Forno & Marco Battiato

  2. Institutes of Physical Science and Information Technology, Anhui University, Hefei, P.R. China

    Xue Liu

  3. Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore

    Kristina Vaklinova, Ho Yi Wei, Kostya S. Novoselov & Maciej Koperski

  4. Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Republic of Singapore

    T. Thu Ha Do

  5. Department of Physics, National University of Singapore, Singapore, Singapore

    Ho Yi Wei

  6. National Institute for Materials Science, Tsukuba, Japan

    K. Watanabe & T. Taniguchi

  7. Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore

    Kostya S. Novoselov & Maciej Koperski

  8. State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, P.R. China

    Qihua Xiong

  9. Frontier Science Center for Quantum Information, Beijing, P.R. China

    Qihua Xiong

  10. Collaborative Innovation Center of Quantum Matter, Beijing, P.R. China

    Qihua Xiong

  11. Beijing Academy of Quantum Information Sciences, Beijing, P.R. China

    Qihua Xiong

Authors
  1. Andrés Granados del Águila
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Contributions

A.G.d.Á. and Q.X. started the project. A.G.d.Á. conceived and designed the experiments. Y.R.W. and X.L. designed and fabricated the large-area devices. K.V. fabricated the hBN-encapsulated MoS2 heterostructures. A.G.d.Á., Y.R.W., X.L. and A.F. performed the experiments. M.B., I.W. and S.D.F. performed the theoretical transport simulations. M.B. and I.W. performed the mean-field calculations. Q.X., M.B., M.K., K.S.N., Y.R.W. and T.T.H.D. intensively discussed the results and the manuscript during its preparation. A.G.d.Á. analysed and interpreted the data and wrote the manuscript with the help of all coauthors.

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Correspondence to Andrés Granados del Águila or Qihua Xiong.

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Supplementary Information

Materials and methods, supplementary text, notes and discussions, and Figs. 1–41.

Supporting Video

Video recording the acquisition of PL images under a continuous gate sweep, from +20 V to −60 V, at fixed excitation power and temperature.

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del Águila, A.G., Wong, Y.R., Wadgaonkar, I. et al. Ultrafast exciton fluid flow in an atomically thin MoS2 semiconductor. Nat. Nanotechnol. 18, 1012–1019 (2023). https://doi.org/10.1038/s41565-023-01438-8

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