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Valley-polarized exciton–polaritons in a monolayer semiconductor

Nature Photonics volume 11, pages 431–435 (2017)Cite this article

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Abstract

Single layers of transition metal dichalcogenides are two-dimensional (2D) direct-bandgap semiconductors with degenerate, but inequivalent, ‘valleys’ in the electronic structure that can be selectively excited by polarized light. Coherent superpositions of light and matter, exciton–polaritons, have been observed when these materials are strongly coupled to photons, but these hybrid quasiparticles do not harness the valley sensitivity of the monolayer semiconductors. Here, we observe valley-polarized exciton–polaritons in monolayers of MoS2 embedded in a dielectric microcavity. These light–matter quasiparticles emit polarized light with spectral Rabi splitting and anticrossing indicative of strongly coupled exciton–polaritons in the topologically separate spin-coupled valleys. The interplay of intervalley depolarization and cavity-modified exciton dynamics in the high-cooperativity regime causes valley-polarized exciton–polaritons to persist at room temperature, distinct from the vanishing polarization in bare monolayers. Achieving polarization-sensitive polaritonic devices operating at room temperature presents a pathway for manipulating novel valley degrees of freedom in coherent states of light and matter.

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Figure 1: Valley-polarized exciton–polaritons in MC-MoS2.
Figure 2: The dispersion of exciton–polaritons in MoS2.
Figure 3: Valley-polarized emission.
Figure 4: Temperature-dependent valley-polarized exciton–polariton emission.

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Acknowledgements

This research is supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under award no. DE-SC0012130 (cavity spectroscopy), by the National Science Foundation MRSEC program under grant no. DMR-1121262 (transfer and device assembly), and by the National Science Foundation under grant no. DMR-1507810 (CVD growth). This work made use of the EPIC and KECK-II facilities of the NUANCE Center at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205); the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. This work utilized Northwestern University Micro/Nano Fabrication Facility (NUFAB), which is partially supported by Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205), the Materials Research Science and Engineering Center (NSF DMR-1121262), the State of Illinois, and Northwestern University. J.D.C. is supported by the Department of Defense through the National Defense Science and Engineering Fellowship (NDSEG) Program. J.D.C. also gratefully acknowledges support from the Ryan Fellowship and the IIN. N.P.S. acknowledges support as an Alfred P. Sloan Research Fellow.

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Authors and Affiliations

  1. Department of Physics and Astronomy, Northwestern University, Evanston, 60208, Illinois, USA

    Yen-Jung Chen, Teodor K. Stanev & Nathaniel P. Stern

  2. Department of Materials Science and Engineering, Northwestern University, Evanston, 60208, Illinois, USA

    Jeffrey D. Cain & Vinayak P. Dravid

  3. International Institute for Nanotechnology, Northwestern University, Evanston, 60208, Illinois, USA

    Jeffrey D. Cain & Vinayak P. Dravid

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  1. Yen-Jung Chen
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Contributions

N.P.S. and Y.-J.C. conceived the experiments. Y.-J.C. fabricated the MC. J.D.C. and V.P.D. synthesized the monolayers. T.K.S. and Y.-J.C. performed material characterization and transfer. Y.-J.C. performed measurements and modelling. Y.-J.C. and N.P.S. co-wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Nathaniel P. Stern.

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Chen, YJ., Cain, J., Stanev, T. et al. Valley-polarized exciton–polaritons in a monolayer semiconductor. Nature Photon 11, 431–435 (2017). https://doi.org/10.1038/nphoton.2017.86

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