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Nonlinear valley phonon scattering under the strong coupling regime

Abstract

Research efforts of cavity quantum electrodynamics have focused on the manipulation of matter hybridized with photons under the strong coupling regime1,2,3. This has led to striking discoveries including polariton condensation2 and single-photon nonlinearity3, where the phonon scattering plays a critical role1,2,3,4,5,6,7,8,9. However, resolving the phonon scattering remains challenging for its non-radiative complexity. Here we demonstrate nonlinear phonon scattering in monolayer MoS2 that is strongly coupled to a plasmonic cavity mode. By hybridizing excitons and cavity photons, the phonon scattering is equipped with valley degree of freedom and boosted with superlinear enhancement to a stimulated regime, as revealed by Raman spectroscopy and our theoretical model. The valley polarization is drastically enhanced and sustained throughout the stimulated regime, suggesting a coherent scattering process enabled by the strong coupling. Our findings clarify the feasibility of valley–cavity-based systems for lighting, imaging, optical information processing and manipulating quantum correlations in cavity quantum electrodynamics2,3,10,11,12,13,14,15,16,17.

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Fig. 1: Schematics of demonstrating phonon scattering under the strong coupling regime.
Fig. 2: Determination of the strong coupling regime in a MoS2 monolayer embedded in plasmonic cavities.
Fig. 3: Direct observation of phonon scattering under the strong coupling regime.
Fig. 4: Uncovering stimulated phonon scattering by polariton-resonance excitation.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported by the King Abdullah University of Science and Technology Office of Sponsored Research award OSR-2016-CRG5-2996, National Science Foundation MRI grant 1725335 and the Ernest S. Kuh Endowed Chair Professorship. X.L. also acknowledges support from the National Natural Science Foundation of China (grant nos 12074297 and 62005202). J.-F.L. acknowledges support from National Natural Science Foundation of China (grant no. 21925404) and National Key Research and Development Program of China (2019YFA0705400). Y.-H.L. acknowledges support from the Ministry of Science and Technology (MoST 109-2124-M-007-001-MY3; 108-2112-M-007-006-MY3; 107-2923-M-007-002-MY3), the Frontier Research Center on Fundamental and Applied Sciences of Matters and the Center for Quantum Technology of National Tsing-Hua University.

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Contributions

X.L. and J.Y. conceived the ideas and designed the experiments. X.L., J.Y. and S.Y. conducted the experiments. J.Y. performed finite element methods simulations and the theoretical modelling. E.-C.L. and Y.-H.L synthesized the CVD monolayer MoS2 sample. Y.-J.Z. and J.-F.L. synthesized the shell-isolated nanoparticles. X.Z. supervised the research. X.L. and J.Y. analysed the data and wrote the manuscript. All authors contributed to data interpretation and editing the manuscript.

Corresponding author

Correspondence to Xiang Zhang.

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The authors declare no competing interests.

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Peer review information Nature Materials thanks Jeremy Baumberg and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Notes 1 and 2, Figs. 1–19, Table 1 and references.

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Liu, X., Yi, J., Yang, S. et al. Nonlinear valley phonon scattering under the strong coupling regime. Nat. Mater. (2021). https://doi.org/10.1038/s41563-021-00972-x

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