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Fractional charge and quantized current in the quantum spin Hall state

Nature Physics volume 4, pages 273–276 (2008)Cite this article

Abstract

Soon after the theoretical proposal of the intrinsic spin Hall effect1,2 in doped semiconductors, the concept of a time-reversal invariant spin Hall insulator3 was introduced. In the extreme quantum limit, a quantum spin Hall (QSH) insulator state has been proposed for various systems4,5,6. Recently, the QSH effect has been theoretically proposed6 and experimentally observed7 in HgTe quantum wells. One central question, however, remains unanswered—what is the direct experimental manifestation of this topologically non-trivial state of matter? In the case of the quantum Hall effect, it is the quantization of the Hall conductance and the fractional charge of quasiparticles, which are results of non-trivial topological structure. Here, we predict that for the QSH state a magnetic domain wall induces a localized state with half the charge of an electron. We also show that a rotating magnetic field can induce a quantized d.c. electric current, and vice versa. Both of these physical phenomena are expected to be direct and experimentally observable consequences of the non-trivial topology of the QSH state.

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Figure 1: Illustrations of proposed phenomena.
Figure 2: Experimental geometry of the SET device and proposed signature of static fractional charge.
Figure 3: Experimental geometry for current generated from adiabatic pumping.

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Acknowledgements

We wish to thank B. A. Bernevig, H. Buhmann, X. Dai, C. L. Kane, M. Koenig and L. Molenkamp for insightful discussions. We acknowledge C.-X. Liu for sharing his unpublished numerical results. This work is supported by the NSF through the grants DMR-0342832, by the US Department of Energy, Office of Basic Energy Sciences under contract DE-AC03-76SF00515, and the Focus Center Research Program (FCRP) Center on Functional Engineered Nanoarchitectonics (FENA).

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  1. Department of Physics, McCullough Building, Stanford University, Stanford, California 94305-4045, USA

    Xiao-Liang Qi, Taylor L. Hughes & Shou-Cheng Zhang

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  1. Xiao-Liang Qi
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  2. Taylor L. Hughes
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Correspondence to Shou-Cheng Zhang.

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Qi, XL., Hughes, T. & Zhang, SC. Fractional charge and quantized current in the quantum spin Hall state. Nature Phys 4, 273–276 (2008). https://doi.org/10.1038/nphys913

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