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High-precision realization of robust quantum anomalous Hall state in a hard ferromagnetic topological insulator

Abstract

The discovery of the quantum Hall (QH) effect led to the realization of a topological electronic state with dissipationless currents circulating in one direction along the edge of a two-dimensional electron layer under a strong magnetic field1,2. The quantum anomalous Hall (QAH) effect shares a similar physical phenomenon to that of the QH effect, whereas its physical origin relies on the intrinsic spin–orbit coupling and ferromagnetism3,4,5,6,7,8,9,10,11,12,13,14,15,16. Here, we report the experimental observation of the QAH state in V-doped (Bi,Sb)2Te3 films with the zero-field longitudinal resistance down to 0.00013 ± 0.00007h/e2 (~3.35 ± 1.76 Ω), Hall conductance reaching 0.9998 ± 0.0006e2/h and the Hall angle becoming as high as 89.993° ± 0.004° at T = 25 mK. A further advantage of this system comes from the fact that it is a hard ferromagnet with a large coercive field (Hc > 1.0 T) and a relative high Curie temperature. This realization of a robust QAH state in hard ferromagnetic topological insulators (FMTIs) is a major step towards dissipationless electronic applications in the absence of external fields.

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Figure 1: The QAH effect in a 4QL (Bi0.29Sb0.71)1.89V0.11Te3 film (sample S1) measured at 25 mK.
Figure 2: Temperature dependence of QAH behaviour in a 4QL (Bi0.29Sb0.71)1.89V0.11Te3 film (sample S1).
Figure 3: Comparison of the ferromagnetic properties in Cr- and V-doped Sb2Te3.
Figure 4: The self-driven QAH state in a different 4QL (Bi0.29Sb0.71)1.89V0.11Te3 film (sample S2).

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Acknowledgements

We are grateful to P. Wei, J. Liu, L. Fu, N. Samarth, J. Jain, G. Csathy and Z. Fang for helpful discussions, and F. Katmis, W. J. Fang, C. Settens and J. Kong for technical support in characterizing the samples. This research is supported by grants from NSF (DMR-1207469), NSF (DMR-0907007), NSF(ECCS-1402738), ONR (N00014-13-1-0301), NSF (DMR-0820404, DMR-1420620, Penn State MRSEC), NSF (DMR-1103159), DOE (DE-AC02-76SF00515), DARPA (N66001-11-1-4105) and the STC Center for Integrated Quantum Materials under NSF grant DMR-1231319.

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C-Z.C., M.H.W.C. and J.S.M. conceived and designed the research. C-Z.C. grew the material with the help of J.S.M. C-Z.C. performed characterization studies of the samples with the help of B.A.A. and D.H. W.Z. made the devices and performed the transport measurements with the help of C-Z.C., D.Y.K. and M.H.W.C. C.L., H.Z. and S-C.Z. provided theoretical support. C-Z.C., C.L. and M.H.W.C. analysed the data and wrote the manuscript with contributions from all authors.

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Correspondence to Cui-Zu Chang or Weiwei Zhao or Jagadeesh S. Moodera.

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The authors declare no competing financial interests.

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Chang, CZ., Zhao, W., Kim, D. et al. High-precision realization of robust quantum anomalous Hall state in a hard ferromagnetic topological insulator. Nature Mater 14, 473–477 (2015). https://doi.org/10.1038/nmat4204

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