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Imaging exciton–polariton transport in MoSe2 waveguides


The exciton–polariton (EP), a half-light and half-matter quasiparticle, is potentially an important element for future photonic and quantum technologies1,2,3,4. It provides both strong light–matter interactions and long-distance propagation that is necessary for applications associated with energy or information transfer. Recently, strongly coupled cavity EPs at room temperature have been demonstrated in van der Waals (vdW) materials due to their strongly bound excitons5,6,7,8,9. Here, we report a nano-optical imaging study of waveguide EPs in MoSe2, a prototypical vdW semiconductor. The measured propagation length of the EPs is sensitive to the excitation photon energy and reaches over 12 µm. The polariton wavelength can be conveniently altered from 600 nm down to 300 nm by controlling the waveguide thickness. Furthermore, we found an intriguing back-bending polariton dispersion close to the exciton resonance. The observed EPs in vdW semiconductors could be useful in future nanophotonic circuits operating in the near-infrared to visible spectral regions.

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Figure 1: Nano-optical imaging of a MoSe2 planar waveguide.
Figure 2: Edge-orientation dependence study.
Figure 3: Dispersion analysis.
Figure 4: Waveguide-thickness dependence study.

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F.H., Y.L. and Z.F. acknowledge start-up support from Iowa State University and Ames Laboratory. The nano-optical imaging set-up was partially supported by the W. M. Keck foundation. The work at the University of Washington was supported by the US Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division (DE-SC0008145 and SC0012509). The work at Oak Ridge National Laboratory (J.Y. and D.G.M.) was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

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Z.F. conceived the ideas and designed the experiments. F.H. carried out the s-SNOM experiments and collected the data. Z.F., F.H. and Y.L. performed theoretical analyses and modelling of the data. X.X., M.E.S., J.Y. and D.G.M. synthesized the MoSe2 crystals and fabricated the waveguide devices. Z.F., X.X., F.H. and Y.L. wrote the paper.

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Correspondence to Z. Fei.

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The authors declare no competing financial interests.

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Hu, F., Luan, Y., Scott, M. et al. Imaging exciton–polariton transport in MoSe2 waveguides. Nature Photon 11, 356–360 (2017).

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