Affiliation:
1. Physikalisches Institut (EP III), Universität Würzburg, D-97074 Würzburg, Germany.
2. Department of Physics, McCullough Building, Stanford University, Stanford, CA 94305–4045, USA.
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 2
e
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.
Publisher
American Association for the Advancement of Science (AAAS)
Cited by
5156 articles.
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