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 2e2/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.
- Publication:
-
Science
- Pub Date:
- November 2007
- DOI:
- 10.1126/science.1148047
- arXiv:
- arXiv:0710.0582
- Bibcode:
- 2007Sci...318..766K
- Keywords:
-
- APP PHYSICS;
- Condensed Matter - Mesoscopic Systems and Quantum Hall Effect
- E-Print:
- 16 pages, 5 figures