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Quantum Spin Hall Insulator State in HgTe Quantum Wells

2007; American Association for the Advancement of Science; Volume: 318; Issue: 5851 Linguagem: Inglês

10.1126/science.1148047

1095-9203

Markus König, S. Wiedmann, C. Brüne, Andreas Roth, H. Buhmann, L. W. Molenkamp, Xiao-Liang Qi, Shou-Cheng Zhang,

Graphene research and applications

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.