Abstract
Recently discovered materials called three-dimensional topological insulators1,2,3,4,5 constitute examples of symmetry-protected topological states in the absence of applied magnetic fields and cryogenic temperatures. A hallmark characteristic of these non-magnetic bulk insulators is their protected metallic Dirac fermion-like surface states. Electrons in these surface states are spin polarized with their spins governed by their momentum, resulting in a helical spin texture in momentum space6. Spin- and angle-resolved photoemission spectroscopy has been the only tool capable of directly observing this central feature with simultaneous energy, momentum and spin sensitivity6,7,8,9,10,11,12. By using an innovative photoelectron spectrometer13 with a high-flux laser-based light source, we discovered a surprising property of these surface electrons. We found that the spin polarization of the resulting photoelectrons can be manipulated in three dimensions through selection of the light polarization. These effects are due to the spin-dependent interaction of the helical surface electrons with light, which originates from strong spin–orbit coupling. Our results illustrate unusual scenarios in which the spin polarization of photoelectrons is completely different from that of the originating initial states. The results also provide the basis for a source of highly spin-polarized electrons with tunable polarization direction.
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Change history
13 March 2013
In the version of this Letter originally published online, in Figure 4a, the angle between the +x direction and the spin direction at momentum k should have been labelled θs, and the angle between the +x direction and k should have been labelled θk. This error has now been corrected in all versions of the Letter.
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Acknowledgements
We thank G. Lebedev and W. Wan for work with the electron optics, W. Zhang, D. A. Siegel, C. L. Smallwood and T. Miller for useful discussions, H. Wang and R. A. Kaindl for advice with optics, and A. Bostwick for help with software development. This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the US Department of Energy under Contract No. DE-AC02-05CH11231 (Lawrence Berkeley National Laboratory). Higher-photon-energy photoemission work was performed at the Advanced Light Source, Lawrence Berkeley National Laboratory, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231.
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C.J. developed the experimental system. C.J., C-H.P. and C.H. devised the experiment. C.J. and K.G. carried out the experiment. C.J. analysed the experimental data. Calculations were performed by C-H.P., S.G.L. and D-H. L. Samples were prepared by C.R.R. and R.J.B. Synchrotron data were acquired by J.D.D., C.J. and K.G. Z.H. and A.L. were responsible for experiment planning and infrastructure. All authors contributed to the interpretation and writing of the manuscript.
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Jozwiak, C., Park, CH., Gotlieb, K. et al. Photoelectron spin-flipping and texture manipulation in a topological insulator. Nature Phys 9, 293–298 (2013). https://doi.org/10.1038/nphys2572
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DOI: https://doi.org/10.1038/nphys2572
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