Abstract
Methods to generate spin-polarized electronic states in non-magnetic solids are strongly desired to enable all-electrical manipulation of electron spins for new quantum devices1. This is generally accepted to require breaking global structural inversion symmetry1,2,3,4,5. In contrast, here we report the observation from spin- and angle-resolved photoemission spectroscopy of spin-polarized bulk states in the centrosymmetric transition-metal dichalcogenide WSe2. Mediated by a lack of inversion symmetry in constituent structural units of the bulk crystal where the electronic states are localized6, we show how spin splittings up to ∼0.5 eV result, with a spin texture that is strongly modulated in both real and momentum space. Through this, our study provides direct experimental evidence for a putative locking of the spin with the layer and valley pseudospins in transition-metal dichalcogenides7,8, of key importance for using these compounds in proposed valleytronic devices.
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Acknowledgements
We gratefully acknowledge support from the Engineering and Physical Sciences Research Council, UK, the VILLUM foundation, the Calipso program, TRF-SUT Grant RSA5680052 and NANOTEC, Thailand through the CoE Network. P.D.C.K. acknowledges support from the Royal Society through a University Research Fellowship. M.S.B. was supported by a Grant-in-Aid for Scientific Research (S) (No. 24224009) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. The experiments at the MAX IV Laboratory were made possible through funding from the Swedish Research Council and the Knut and Alice Wallenberg Foundation.
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J.M.R., F.M., M.D., M.M., L.B., C.G., W.M., J.W.W. and P.D.C.K. measured the experimental data. J.M.R., F.M., J.W.W. and P.D.C.K. analysed the data. M.S.B. performed the electronic structure calculations. T.T. grew the samples. M.L. and T.B. maintained the spin-ARPES end stations and M.H. and T.K.K. maintained the ARPES end stations, respectively, and provided experimental support. P.D.C.K., J.W.W., M.S.B., P.H. and H.T. provided the project infrastructure. All authors discussed the results and their interpretation. P.D.C.K. and J.M.R. wrote the manuscript with input and discussion from all co-authors. P.D.C.K. was responsible for overall project planning and direction.
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Riley, J., Mazzola, F., Dendzik, M. et al. Direct observation of spin-polarized bulk bands in an inversion-symmetric semiconductor. Nature Phys 10, 835–839 (2014). https://doi.org/10.1038/nphys3105
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DOI: https://doi.org/10.1038/nphys3105
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