Strong light–matter coupling in two-dimensional atomic crystals

Journal name:
Nature Photonics
Volume:
9,
Pages:
30–34
Year published:
DOI:
doi:10.1038/nphoton.2014.304
Received
Accepted
Published online

Abstract

Two-dimensional atomic crystals of graphene, as well as transition-metal dichalcogenides, have emerged as a class of materials that demonstrate strong interaction with light. This interaction can be further controlled by embedding such materials into optical microcavities. When the interaction rate is engineered to be faster than dissipation from the light and matter entities, one reaches the ‘strong coupling’ regime. This results in the formation of half-light, half-matter bosonic quasiparticles called microcavity polaritons. Here, we report evidence of strong light–matter coupling and the formation of microcavity polaritons in a two-dimensional atomic crystal of molybdenum disulphide (MoS2) embedded inside a dielectric microcavity at room temperature. A Rabi splitting of 46 ± 3 meV is observed in angle-resolved reflectivity and photoluminescence spectra due to coupling between the two-dimensional excitons and the cavity photons. Realizing strong coupling at room temperature in two-dimensional materials that offer a disorder-free potential landscape provides an attractive route for the development of practical polaritonic devices.

At a glance

Figures

  1. Structure and optical properties of the CVD-grown MoS2 microcavity.
    Figure 1: Structure and optical properties of the CVD-grown MoS2 microcavity.

    a, Chemical structure of the MoS2 monolayer. b, SEM image of the MoS2 monolayer as grown on a SiO2/Si substrate. Scale bar, 10 µm. Dark areas are the active MoS2 monolayers. c, Schematic of the microcavity structure. d, Reflectivity spectra for a passive location corresponding to an area without MoS2 monolayer (black line) and for an active location with MoS2 monolayer (blue). The vertical red dashed line represents the MoS2 exciton (exA) energy.

  2. Angle-resolved reflectivity spectra of the microcavity.
    Figure 2: Angle-resolved reflectivity spectra of the microcavity.

    a, Angle-resolved reflectivity spectra for TM polarization from 7.5° to 30°. The vertical red dashed line represents the MoS2 exA energy. Red curves trace the dispersion of microcavity polariton modes. b,c, Expanded views of reflectivity spectral features at 20° (b) and 7.5° (c). Both spectra show two well-defined polariton states at both sides of the exA energy.

  3. Dispersion of microcavity polaritons.
    Figure 3: Dispersion of microcavity polaritons.

    a, Dispersion relation extracted from the angle-resolved reflectivity spectra. Red spheres with error bars are the polariton energies obtained from the reflectivity spectra. The horizontal black dashed line represents the exA energy. The black short-dashed curve represents the cavity modes. The two black solid curves correspond to theoretical fits of the polariton branches using a coupled oscillator model. b,c, Hopfield coefficients for the microcavity polariton branches (UPB in b and LPB in c, calculated using the coupled oscillator model). These provide the weighting of each constituent. Black stars correspond to the coefficients of the cavity photon and the red spheres to those of the exciton.

  4. Angle-resolved photoluminescence spectra of the microcavity.
    Figure 4: Angle-resolved photoluminescence spectra of the microcavity.

    a, Angle-resolved photoluminescence spectra for TM polarization from 2.5° to 35°. The vertical red dashed line represents the MoS2 exA energy and the red curves trace the dispersion of microcavity polariton modes. a.u., arbitrary units. b, Expanded view of photoluminescence spectral features at 7.5°. A relatively weak LPB photoluminescence peak is observed around 1.826 eV, as well as a prominent UPB peak at 1.876 eV. The photoluminescence spectrum is also fitted to multiple Lorentzian peaks to locate the exact photoluminescence peak positions. c, The energy versus angle dispersion, extracted from the angle-resolved photoluminescence spectra, agrees well with the reflectivity dispersion. The dispersion is fitted to a coupled oscillator model, showing Rabi splitting of ∼46 ± 3 meV, similar to that observed in the reflectivity experiments.

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Affiliations

  1. Department of Physics, City College of New York, New York, New York 10031, USA

    • Xiaoze Liu,
    • Tal Galfsky,
    • Zheng Sun &
    • Vinod M. Menon
  2. Department of Physics, Queens College & Graduate Centre, City University of New York, New York, New York 11367, USA

    • Xiaoze Liu,
    • Tal Galfsky,
    • Zheng Sun &
    • Vinod M. Menon
  3. Department of Electrical Engineering, PO Box 208267, Yale University, New Haven, Connecticut 06520, USA

    • Fengnian Xia
  4. Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan

    • Erh-chen Lin &
    • Yi-Hsien Lee
  5. Department of Engineering Physics, École Polytechnique de Montréal, Montréal, Quebec, Canada

    • Stéphane Kéna-Cohen

Contributions

V.M. and F.X. initiated the project. X.L., V.M. and F.X. designed the experiments. X.L. fabricated the microcavity samples. X.L. and Z.S. collected the data and X.L., S.K.C. and V.M. analysed it. E.C.L. and Y.H.L. grew the CVD monolayer MoS2. X.L. and T.G. performed the theoretical modelling. All authors contributed to the discussion of the results and writing the manuscript.

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