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Giant optical nonlinearity of Fermi polarons in atomically thin semiconductors

Nature Photonics (2024)Cite this article

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Abstract

Realizing strong nonlinear optical responses is a long-standing goal of both fundamental and technological importance. Recently, substantial efforts have been focused on exploring excitons in solids to achieve nonlinearities even down to few-photon levels. However, a crucial tradeoff arises as strong light–matter interactions require large oscillator strength and short radiative lifetime of excitons, which limits their nonlinearity. Here we experimentally demonstrate strong nonlinear optical responses with large oscillator strength by exploiting the coupling between excitons and carriers in an atomically thin semiconductor. By controlling the electric field and electrostatic doping of trilayer WSe2, we observe the hybridization between intralayer and interlayer excitons and the formation of Fermi polarons. Substantial optical nonlinearity is observed under continuous-wave and pulsed laser excitation, where the Fermi polaron resonance blueshifts by as much as ~10 meV. Intriguingly, we observe a remarkable asymmetry in the optical nonlinearity between electron and hole doping, which is tunable by the applied electric field. We attribute these features to the optically induced valley polarization due to the interactions between excitons and free charges. Our results establish atomically thin heterostructures as a highly versatile platform for engineering nonlinear optical response with applications to classical and quantum optoelectronics.

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Fig. 1: Dual-gated WSe2 homotrilayer van der Waals heterostructure and their optical characteristics under gating at T = 4 K.
Fig. 2: Nonlinearity in hole-doped homotrilayer WSe2 at T = 4 K.
Fig. 3: Electronic band structure of trilayer WSe2.
Fig. 4: Electric-field-dependent exciton energy and nonlinearity in homotrilayer WSe2 at T = 4 K.

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All other data are available from the corresponding author upon reasonable request. Source data are provided with this paper.

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Acknowledgements

This research is primarily supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences Early Career Research Program, under award no. DE-SC-0022885. The fabrication of samples is supported by the National Science Foundation CAREER Award under award no. DMR-2145712. This research used Quantum Material Press (QPress) of the Center for Functional Nanomaterials (CFN), which is a US Department of Energy, Office of Science User Facility, at Brookhaven National Laboratory under contract no. DE-SC0012704. K.W. and T.T. acknowledge support from the JSPS KAKENHI (grant nos. 20H00354, 21H05233 and 23H02052) and World Premier International Research Center Initiative (WPI), MEXT, Japan, for hBN synthesis.

Author information

Author notes

  1. These authors contributed equally: Liuxin Gu, Lifu Zhang.

Authors and Affiliations

  1. Department of Materials Science and Engineering, University of Maryland, College Park, MD, USA

    Liuxin Gu, Lifu Zhang, Ruihao Ni & You Zhou

  2. Condensed Matter Theory Center, University of Maryland, College Park, MD, USA

    Ming Xie

  3. Max Plank Institute of Quantum Optics, Garching, Germany

    Dominik S. Wild

  4. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, USA

    Suji Park & Houk Jang

  5. Research Center for Electronic and Optical Materials, National Institute for Materials Science, Tsukuba, Japan

    Takashi Taniguchi

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

    Kenji Watanabe

  7. Joint Quantum Institute (JQI), University of Maryland, College Park, MD, USA

    Mohammad Hafezi

  8. Maryland Quantum Materials Center, College Park, MD, USA

    You Zhou

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Contributions

Y.Z. and L.G. conceived the project. L.G. fabricated the samples and performed the experiments. L.Z., R.N., S.P. and H.J. assisted with the sample fabrication. L.Z. and R.N. helped with the optical measurements. M.X., D.S.W., M.H. and Y.Z. contributed to the data analysis and theoretical understanding. T.T. and K.W. provided the hBN samples. L.G. and Y.Z. wrote the paper with extensive input from the other authors.

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Correspondence to You Zhou.

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Nature Photonics thanks Xi Wang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Numerical source data for Fig. 4a–d.

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Gu, L., Zhang, L., Ni, R. et al. Giant optical nonlinearity of Fermi polarons in atomically thin semiconductors. Nat. Photon. (2024). https://doi.org/10.1038/s41566-024-01434-x

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