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Optical valley Hall effect for highly valley-coherent exciton-polaritons in an atomically thin semiconductor

Abstract

Spin–orbit coupling is a fundamental mechanism that connects the spin of a charge carrier with its momentum. In the optical domain, an analogous synthetic spin–orbit coupling is accessible by engineering optical anisotropies in photonic materials. Both yield the possibility of creating devices that directly harness spin and polarization as information carriers. Atomically thin transition metal dichalcogenides promise intrinsic spin-valley Hall features for free carriers, excitons and photons. Here we demonstrate spin- and valley-selective propagation of exciton-polaritons in a monolayer of MoSe2 that is strongly coupled to a microcavity photon mode. In a wire-like device we trace the flow and helicity of exciton-polaritons expanding along its channel. By exciting a coherent superposition of K and K′ tagged polaritons, we observe valley-selective expansion of the polariton cloud without either an external magnetic field or coherent Rayleigh scattering. The observed optical valley Hall effect occurs on a macroscopic scale, offering the potential for applications in spin-valley-locked photonic devices.

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Fig. 1: Sample design and characterization.
Fig. 2: Valley polarization and coherence of polaritons.
Fig. 3: Optical valley Hall effect.

Data availability

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

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Acknowledgements

C.S. acknowledges support from the ERC (Project unLiMIt-2D). The Würzburg group acknowledges support from the State of Bavaria. A.V.K. acknowledges support from Westlake University (Project No. 041020100118). A.V.K. acknowledges the St Petersburg State University for research grant ID 40847559. E.S. acknowledges support from the Grant of the President of the Russian Federation for state support of young Russian scientists No. MK-2839.2019.2 and RFBR Grant No. 17-52-10006. S.K. acknowledges support from the EU (Marie Curie Project TOPOPOLIS). Q.Y. and S.T. acknowledge funding from NSF DMR-1838443 and DMR-1552220. M.M.G. acknowledges partial support from RFBR Project No. 17-02-00383.

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N.L. exfoliated, identified and transferred the monolayer and designed and fabricated the microcavity. Y.Q. and S.T. synthesized the bulk crystal. N.L., Ł.D., S.K., M.K. and P.S. performed experiments. N.L., S.K., M.K., J.B., M.R. and C.S. analysed and interpreted the experimental data, supported by all co-authors. E.S., M.M.G. and A.V.K. provided the theory. N.L. and C.S. wrote the manuscript, with input from all co-authors. C.S. and S.H. initiated the study and guided the work.

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Correspondence to Christian Schneider.

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Lundt, N., Dusanowski, Ł., Sedov, E. et al. Optical valley Hall effect for highly valley-coherent exciton-polaritons in an atomically thin semiconductor. Nat. Nanotechnol. 14, 770–775 (2019). https://doi.org/10.1038/s41565-019-0492-0

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