Quantum Spin Hall Insulator State in HgTe Quantum Wells

Markus Koenig; Steffen Wiedmann; Christoph Bruene; Andreas Roth; Hartmut Buhmann; Laurens W. Molenkamp; Xiao-Liang Qi; Shou-Cheng Zhang

doi:10.1126/science.1148047

arXiv · 0710.0582

Quantum Spin Hall Insulator State in HgTe Quantum Wells

Markus Koenig·Steffen Wiedmann·Christoph Bruene·Andreas Roth·Hartmut Buhmann·Laurens W. Molenkamp·Xiao-Liang Qi·Shou-Cheng Zhang

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Abstract

Recent theory predicted that the Quantum Spin Hall Effect, a fundamentally novel quantum state of matter that exists at zero external magnetic field, may be realized in HgTe/(Hg,Cd)Te quantum wells. We have fabricated such sample structures with low density and high mobility in which we can tune, through an external gate voltage, the carrier conduction from n-type to the p-type, passing through an insulating regime. For thin quantum wells with well width d < 6.3 nm, the insulating regime shows the conventional behavior of vanishingly small conductance at low temperature. However, for thicker quantum wells (d > 6.3 nm), the nominally insulating regime shows a plateau of residual conductance close to 2e^2/h. The residual conductance is independent of the sample width, indicating that it is caused by edge states. Furthermore, the residual conductance is destroyed by a small external magnetic field. The quantum phase transition at the critical thickness, d = 6.3 nm, is also independently determined from the magnetic field induced insulator to metal transition. These observations provide experimental evidence of the quantum spin Hall effect.

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Markus Koenig, Steffen Wiedmann, Christoph Bruene, Andreas Roth, Hartmut Buhmann, Laurens W. Molenkamp, Xiao-Liang Qi, Shou-Cheng Zhang. 2007-10-02. Quantum Spin Hall Insulator State in HgTe Quantum Wells. https://doi.org/10.1126/science.1148047

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