Berlin 2008 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 18: Invited Talk Buhmann

HL 18.1: Hauptvortrag

Dienstag, 26. Februar 2008, 09:30–10:15, ER 270

Quantum Spin Hall Insulator State in HgTe Quantum Wells — •Hartmut Buhmann¹, Markus König¹, Steffen Wiedmann¹, Christoph Brüne¹, Andreas Roth¹, Laurens W. Molenkamp¹, Xiao-Liang Qi², and Shou-Cheng Zhang² — ¹Physikalisches Institut, EP3, Universität Würzburg, Würzburg, Germany — ²Department of Physics, Standford University, Standford CA, USA

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 [1]. 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 ’normal’ quantum wells (well width d < 6.3 nm), the insulating regime showed the conventional behavior of vanishingly small conductance at low temperature. However, for thicker ’inverted’ quantum wells (d > 6.3 nm), the nominally insulating regime showed a plateau of residual conductance close to 2e²/h [2]. Further investigations confirmed that these observations provide experimental evidence of the quantum spin Hall effect.

[1] B.A. Bernevig, T.L. Hughes, S.-C. Zhang, Science 314, 1757 (2006).

[2] M. König, S. Wiedmann, C. Brüne, A. Roth, H. Buhmann, L.W. Molenkamp, X.L. Qi, and S.C. Zhang, Science 318, 766 (2007).