The locking of the electron spin to the valley degree of freedom in transition metal dichalcogenide (TMD) monolayers has seen these materials emerge as a promising platform in valleytronics1,2. When embedded in optical microcavities, the large oscillator strengths of excitonic transitions in TMDs allow the formation of polaritons that are part-light part-matter quasiparticles3,4,5,6,7. Here, we report that polaritons in MoSe2 show an efficient retention of the valley pseudospin contrasting them with excitons and trions in this material. We find that the degree of the valley pseudospin retention is dependent on the photon, exciton and trion fractions in the polariton states. This allows us to conclude that in the polaritonic regime, cavity-modified exciton relaxation inhibits loss of the valley pseudospin. The valley-addressable exciton-polaritons and trion-polaritons presented here offer robust valley-polarized states with the potential for valleytronic devices based on TMDs embedded in photonic structures and valley-dependent nonlinear polariton–polariton interactions.
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We thank the financial support of the Graphene Flagship under grant agreement 696656, the Engineering and Physical Sciences Research Council (EPSRC) grants EP/M012727/1 and EP/J007544/1, European Research Council (ERC) Advanced Grant EXCIPOL no. 320570, and Marie Sklodowska-Curie network Spin-NANO under grant agreement 676108. A.A.P.T., D.N.K. and J.M.S. acknowledge support from the Leverhulme Trust. F.W. acknowledges support from the Royal Academy of Engineering, and K.S.N. from the Royal Society, EPSRC, US Army Research Office and ERC Grant Hetero2D.
The authors declare no competing financial interests.
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Dufferwiel, S., Lyons, T., Solnyshkov, D. et al. Valley-addressable polaritons in atomically thin semiconductors. Nature Photon 11, 497–501 (2017). https://doi.org/10.1038/nphoton.2017.125
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