title: Quantum spin hall insulator state in HgTe quantum wells.
abstract: Recent theory predicted that the quantum spin Hall effect, a fundamentally new quantum state of matter that exists at zero external magnetic field, may be realized in HgTe/(Hg,Cd)Te quantum wells. We fabricated such sample structures with low density and high mobility in which we could tune, through an external gate voltage, the carrier conduction from n-type to p-type, passing through an insulating regime. For thin quantum wells with well width d < 6.3 nanometers, the insulating regime showed the conventional behavior of vanishingly small conductance at low temperature. However, for thicker quantum wells (d > 6.3 nanometers), the nominally insulating regime showed a plateau of residual conductance close to 2e(2)/h, where e is the electron charge and h is Planck's constant. The residual conductance was independent of the sample width, indicating that it is caused by edge states. Furthermore, the residual conductance was destroyed by a small external magnetic field. The quantum phase transition at the critical thickness, d = 6.3 nanometers, was also independently determined from the magnetic field-induced insulator-to-metal transition. These observations provide experimental evidence of the quantum spin Hall effect.
authors: Physikalisches Institut (EP III), Universität Würzburg, D-97074 Würzburg, Germany.
authors: Markus
authors: M
authors: König
authors: Steffen
authors: S
authors: Wiedmann
authors: Christoph
authors: C
authors: Brüne
authors: Andreas
authors: A
authors: Roth
authors: Hartmut
authors: H
authors: Buhmann
authors: Laurens W
authors: LW
authors: Molenkamp
authors: Xiao-Liang
authors: XL
authors: Qi
authors: Shou-Cheng
authors: SC
authors: Zhang