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Science 13 February 2009:
Vol. 323. no. 5916, pp. 919 - 922
DOI: 10.1126/science.1167733
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Reports

Observation of Unconventional Quantum Spin Textures in Topological Insulators

D. Hsieh,1 Y. Xia,1,2 L. Wray,1,3 D. Qian,1 A. Pal,1 J. H. Dil,4,5 J. Osterwalder,5 F. Meier,4,5 G. Bihlmayer,6 C. L. Kane,7 Y. S. Hor,8 R. J. Cava,8 M. Z. Hasan1,2*

A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry–based classification of condensed matter. Exotic spin-transport phenomena, such as the dissipationless quantum spin Hall effect, have been speculated to originate from a topological order whose identification requires a spin-sensitive measurement, which does not exist to this date in any system. Using Mott polarimetry, we probed the spin degrees of freedom and demonstrated that topological quantum numbers are completely determined from spin texture–imaging measurements. Applying this method to Sb and Bi1–xSbx, we identified the origin of its topological order and unusual chiral properties. These results taken together constitute the first observation of surface electrons collectively carrying a topological quantum Berry's phase and definite spin chirality, which are the key electronic properties component for realizing topological quantum computing bits with intrinsic spin Hall–like topological phenomena.

1 Joseph Henry Laboratories of Physics, Department of Physics, Princeton University, Princeton, NJ 08544, USA.
2 Princeton Center for Complex Materials, Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, NJ 08544, USA.
3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94305, USA.
4 Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen, Switzerland.
5 Physik-Institut, Universität Zürich-Irchel, 8057 Zürich, Switzerland.
6 Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich, Germany.
7 Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA.
8 Department of Chemistry, Princeton University, Princeton, NJ 08544, USA.

* To whom correspondence should be addressed. E-mail: mzhasan{at}princeton.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)