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Fermi polaron-polaritons in charge-tunable atomically thin semiconductors

Nature Physics volume 13, pages 255–261 (2017)Cite this article

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Abstract

The dynamics of a mobile quantum impurity in a degenerate Fermi system is a fundamental problem in many-body physics. The interest in this field has been renewed due to recent ground-breaking experiments with ultracold Fermi gases1,2,3,4,5. Optical creation of an exciton or a polariton in a two-dimensional electron system embedded in a microcavity constitutes a new frontier for this field due to an interplay between cavity coupling favouring ultralow-mass polariton formation6 and exciton–electron interactions leading to polaron or trion formation7,8. Here, we present cavity spectroscopy of gate-tunable monolayer MoSe2 (ref. 9) exhibiting strongly bound trion and polaron resonances, as well as non-perturbative coupling to a single microcavity mode10,11. As the electron density is increased, the oscillator strength determined from the polariton splitting is gradually transferred from the higher-energy repulsive exciton-polaron resonance to the lower-energy attractive exciton-polaron state. Simultaneous observation of polariton formation in both attractive and repulsive branches indicates a new regime of polaron physics where the polariton impurity mass can be much smaller than that of the electrons. Our findings shed new light on optical response of semiconductors in the presence of free carriers by identifying the Fermi polaron nature of excitonic resonances and constitute a first step in investigation of a new class of degenerate Bose–Fermi mixtures12,13.

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Figure 1: A MoSe2/hBN/graphene heterostructure in a fibre cavity.
Figure 2: Cavity spectroscopy of the interacting exciton–electron system in the weak-coupling regime.
Figure 3: Cavity spectroscopy of the interacting exciton–electron system in the strong-coupling regime.
Figure 4: Competition between repulsive and attractive polaron resonances.

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Acknowledgements

J. Reichel, A. Kis and R. Schmidt have made invaluable contributions to the experimental and theoretical aspects of this work. The authors also acknowledge many insightful discussions with C. Ciuti, M. Combescot, M. Fleischhauer, L. Glazman, M. Goldstein, F. Grusdt, D. Pimenov and J. von Delft. This work is supported by an ERC Advanced investigator grant (POLTDES), NCCR Quantum Science and Technology (NCCR QSIT), a research instrument of the Swiss National Science Foundation (SNSF), Harvard-MIT CUA, NSF Grant No. DMR-1308435, M. Rössler, the Walter Haefner Foundation and the ETH Foundation.

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Authors and Affiliations

  1. Institute of Quantum Electronics, ETH Zürich, CH-8093 Zürich, Switzerland

    Meinrad Sidler, Patrick Back, Ovidiu Cotlet, Thomas Fink, Martin Kroner & Atac Imamoglu

  2. Physics Department, Emory University, Atlanta, Georgia 22138, USA

    Ajit Srivastava

  3. Physics Department, Harvard University, Cambridge, Massachusetts 02138, USA

    Eugene Demler

Authors
  1. Meinrad Sidler
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  2. Patrick Back
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  3. Ovidiu Cotlet
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  4. Ajit Srivastava
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  8. Atac Imamoglu
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Contributions

M.S. and A.I. designed and supervised the experiment. M.S. carried out the measurements. P.B. fabricated the sample. T.F. and M.S. designed and assembled the cavity structure. A.S. and M.K. helped with the experiments. O.C., E.D. and A.I. developed the theoretical model. O.C. carried out the calculations. M.S., O.C. and A.I. wrote the manuscript.

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Correspondence to Meinrad Sidler or Atac Imamoglu.

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The authors declare no competing financial interests.

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Sidler, M., Back, P., Cotlet, O. et al. Fermi polaron-polaritons in charge-tunable atomically thin semiconductors. Nature Phys 13, 255–261 (2017). https://doi.org/10.1038/nphys3949

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