Abstract
Coupling degrees of freedom of distinct nature plays a critical role in numerous physical phenomena1,2,3,4,5,6,7,8,9,10. The recent emergence of layered materials11,12,13 provides a laboratory for studying the interplay between internal quantum degrees of freedom of electrons14,15. Here we report new coupling phenomena connecting real spin with layer pseudospins in bilayer WSe2. In polarization-resolved photoluminescence measurements, we observe large spin orientation of neutral and charged excitons by both circularly and linearly polarized excitation, with the trion spectrum splitting into a doublet at large vertical electrical field. These observations can be explained as a locking of spin and layer pseudospin in a given valley15, where the doublet implies an electrically induced spin splitting. The observed distinctive behaviour of the trion doublet under polarized excitation further provides spectroscopic evidence of interlayer and intralayer trion species, a promising step towards optical manipulation in van der Waals heterostructures16 through interlayer excitons.
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Acknowledgements
The authors wish to acknowledge G. Liu and X. Wu for helpful information on the bilayer band structure, and D. Cobden for useful comments. This work is mainly supported by US DoE, BES, Division of Materials Sciences and Engineering (DE-SC0008145). A.M.J. is partially supported by a NSF graduate fellowship (DGE-0718124). H.Y. and W.Y. were supported by the Research Grant Council (HKU705513P) of the government of Hong Kong, and the Croucher Foundation under the Croucher Innovation Award. N.J.G., J.Y. and D.G.M. were supported by US DoE, BES, Materials Sciences and Engineering Division. Device fabrication was completed at the University of Washington Microfabrication Facility and NSF-funded Nanotech User Facility. Second harmonic generation is done at Garvey Imaging Core of the Institute for Stem Cell and Regenerative Medicine.
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X.X. and W.Y. conceived the experiments. A.M.J. performed the measurements. J.S.R. fabricated the devices, assisted by A.M.J. and P.K. H.Y., W.Y., A.M.J. and X.X. analysed the results. The WSe2 crystals were synthesized by N.J.G., J.Y. and D.G.M., who also performed characterization measurements of bulk crystals. A.M.J., X.X., H.Y. and W.Y. co-wrote the paper. All authors discussed the results and commented on the manuscript.
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Jones, A., Yu, H., Ross, J. et al. Spin–layer locking effects in optical orientation of exciton spin in bilayer WSe2. Nature Phys 10, 130–134 (2014). https://doi.org/10.1038/nphys2848
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DOI: https://doi.org/10.1038/nphys2848
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