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A tunable topological insulator in the spin helical Dirac transport regime

Hsieh, D. and Xia, Y. and Qian, D. and Wray, L. and Dil, J. H. and Meier, F. and Osterwalder, J. and Patthey, L. and Checkelsky, J. G. and Ong, N. P. and Fedorov, A. V. and Lin, H. and Bansil, A. and Grauer, D. and Hor, Y. S. and Cava, R. J. and Hasan, M. Z. (2009) A tunable topological insulator in the spin helical Dirac transport regime. Nature, 460 (7259). pp. 1101-1105. ISSN 0028-0836.

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Helical Dirac fermions—charge carriers that behave as massless relativistic particles with an intrinsic angular momentum (spin) locked to its translational momentum—are proposed to be the key to realizing fundamentally new phenomena in condensed matter physics. Prominent examples include the anomalous quantization of magneto-electric coupling, half-fermion states that are their own antiparticle, and charge fractionalization in a Bose– Einstein condensate, all of which are not possible with conventional Dirac fermions of the graphene variety. Helical Dirac fermions have so far remained elusive owing to the lack of necessary spin-sensitive measurements and because such fermions are forbidden to exist in conventional materials harbouring relativistic electrons, such as graphene or bismuth. It has recently been proposed that helical Dirac fermions may exist at the edges of certain types of topologically ordered insulators—materials with a bulk insulating gap of spin–orbit origin and surface states protected against scattering by time-reversal symmetry—and that their peculiar properties may be accessed provided the insulator is tuned into the so-called topological transport regime. However, helical Dirac fermions have not been observed in existing topological insulators. Here we report the realization and characterization of a tunable topological insulator in a bismuthbased class of material by combining spin-imaging and momentum-resolved spectroscopies, bulk charge compensation, Hall transport measurements and surface quantum control. Our results reveal a spin-momentum locked Dirac cone carrying a nontrivial Berry’s phase that is nearly 100 per cent spin-polarized, which exhibits a tunable topological fermion density in the vicinity of the Kramers point and can be driven to the long-sought topological spin transport regime. The observed topological nodal state is shown to be protected even up to 300 K. Our demonstration of room-temperature topological order and non-trivial spintexture in stoichiometric Bi_2Se_3.M_x (M_x indicates surface doping or gating control) paves the way for future graphene-like studies of topological insulators, and applications of the observed spinpolarized edge channels in spintronic and computing technologies possibly at room temperature.

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Hsieh, D.0000-0002-0812-955X
Additional Information:© 2014 Macmillan Publishers Limited. Received 30 April 2009; Accepted 29 June 2009; Published online 20 July 2009. We acknowledge the following people for discussions: P. W. Anderson, B. Altshuler, L. Balents, M. R. Beasley, B. A. Bernevig, C. Callan, J. C. Davis, H. Fertig, E. Fradkin, L. Fu, D. Gross, D. Haldane, K. Le Hur, B. I. Halperin, D. A. Huse, C. L. Kane, C. Kallin, E. A. Kim, R. B. Laughlin, D.-H. Lee, P. A. Lee, J. E. Moore, A. J. Millis, A. H. Castro Neto, J. Orenstein, P. Phillips, S. Sachdev, Dan C. Tsui, A. Vishwanath, F. Wilczek, X.-G. Wen and A. Yazdani. The spin-resolved and spin-integrated ARPES measurements using synchrotron X-ray facilities and theoretical computations are supported by the Basic Energy Sciences of the US Department of Energy (DE-FG-02-05ER46200, AC03-76SF00098 and DE-FG02-07ER46352) and by the Swiss Light Source, Paul Scherrer Institute. Materials growth and characterization are supported by the NSF through the Princeton Center for Complex Materials (DMR-0819860) and Princeton University. M.Z.H. acknowledges additional support from the A. P. Sloan Foundation, an R. H. Dicke fellowship research grant and the Kavli Institute of Theoretical Physics at Santa Barbara.
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG-02-05ER46200
Department of Energy (DOE)AC03-76SF00098
Department of Energy (DOE)DE-FG02-07ER46352
Paul Scherrer Institute, Swiss Light SourceUNSPECIFIED
Princeton UniversityUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
R. H. Dicke FellowshipUNSPECIFIED
Kavli Institute for Theoretical PhysicsUNSPECIFIED
Issue or Number:7259
Record Number:CaltechAUTHORS:20140909-135533013
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49499
Deposited By: Joy Painter
Deposited On:10 Sep 2014 20:20
Last Modified:22 Aug 2019 22:01

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