Physics – Condensed Matter – Mesoscale and Nanoscale Physics
Scientific paper
2007-10-02
Science, Sciencexpress 20 September 2007
Physics
Condensed Matter
Mesoscale and Nanoscale Physics
16 pages, 5 figures
Scientific paper
10.1126/science.1148047
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.
Bruene Christoph
Buhmann Hartmut
Koenig Markus
Molenkamp Laurens W.
Qi Xiao-Liang
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