Fractional charge and quantized current in the quantum spin Hall state

Abstract

Quantum spin Hall insulators are new states of matter that were recently predicted and observed. A theoretical work now explores distinct experimental manifestations resulting from the exotic behaviour that characterizes these structures. 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.

Cite this article

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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