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Spin-filtered edge states with an electrically tunable gap in a two-dimensional topological crystalline insulator


Three-dimensional topological crystalline insulators were recently predicted and observed in the SnTe class of IV–VI semiconductors, which host metallic surface states protected by crystal symmetries. In this work, we study thin films of these materials and expose their potential for device applications. We demonstrate that thin films of SnTe and Pb1−xSnxSe(Te) grown along the (001) direction are topologically non-trivial in a wide range of film thickness and carry conducting spin-filtered edge states that are protected by the (001) mirror symmetry through a topological invariant. Application of an electric field perpendicular to the film will break the mirror symmetry and generate a bandgap in these edge states. This functionality motivates us to propose a topological transistor device in which charge and spin transport are maximally entangled and simultaneously controlled by an electric field. The high on/off operation speed and coupling of spin and charge in such a device may lead to electronic and spintronic applications for topological crystalline insulators.

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Figure 1: Energy-level diagram of TCI thin films.
Figure 2: Band inversion in SnTe films.
Figure 3: Phase diagram of 2D TCIs.
Figure 4: Effect of electric field on edge states.
Figure 5: Topological transistor.
Figure 6: Berry curvature.

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We thank Y. Ando and A. Young for helpful comments and suggestions. This work is supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0010526. T.H.H. acknowledges support under NSF Graduate Research Fellowship No. 0645960. J.L and W.D. acknowledge support from the Ministry of Science and Technology of China (Grant Nos 2011CB921901 and 2011CB606405) and the National Natural Science Foundation of China (Grant No. 11074139). P.W. and J.M. are grateful for support from the MIT MRSEC through the MRSEC Program of the NSF under award number DMR-0819762, as well as NSF DMR grants 1207469 and ONR grant N00014-13-1-0301.

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J.L. performed band-structure and mirror Chern number calculations. T.H.H. performed theoretical analysis with contributions from J.L. T.H.H. and L.F. wrote the manuscript with contributions from all authors. L.F. conceived and supervised the project. All correspondence should be addressed to L.F.

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Correspondence to Liang Fu.

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Liu, J., Hsieh, T., Wei, P. et al. Spin-filtered edge states with an electrically tunable gap in a two-dimensional topological crystalline insulator. Nature Mater 13, 178–183 (2014).

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