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Spin-orbit interaction in semiconductors causes many interesting and potentially useful transport effects, such as e.g. the presently very topical spin-Hall effect[1]. So far no direct evidence for a ballistic, intrinsic SHE (i.e. resulting from the band structure) has been obtained by transport experiments. Here, we demonstrate that in specially designed nanostructures[2], which are based on narrow gap HgTe type-III (a.k.a.inverted) quantum wells, a detection of the spin signal is possible via non-local voltage measurements.
Recently, it was pointed out that such inverted HgTe structures are topologically non-trivial insulators[3], in which the quantum spin Hall insulator state[4] should occur. In this novel quantum state of matter, a pair of spin polarized helical edge channels develops when the bulk of the material is insulating, leading to a quantized conductance. I will present transport data provide very direct evidence for the existence of this third quantum Hall effect: when the bulk of the material is insulating, we observe a quantized electric conductance[5].
Finally, we demonstrate how a combination of the techniques used in the above experiments allows us to verify that the transport in the quantum spin Hall insulator state indeed occurs through spin-polarized helical edge channels.
[1] S. Murakami et al., Science 301 (2003) 1348; J. Sinova et al., Phys. Rev. Lett. 92 (2004) 126603; Y. Kato et al., Science 306 (2004) 1910 %G–%@ and many more. [2] E.M. Hankiewicz, et al., Phys. Rev. B 70 (2004) 241301(R). [3] B.A. Bernevig et al., Science 314 (2006) 1757. [4] C.L. Kane and E.J. Mele, Phys. Rev. Lett. 95 (2005) 146802. [5] M. König et al., Science 318, 766 (2007). |
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