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Nat Commun. 2015 May 26;6:7252. doi: 10.1038/ncomms8252.

Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry.

Author information

1
1] Geballe Laboratory for Advanced Materials, Stanford University, 476 Lomita Mall, Stanford, California 94305, USA [2] Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, USA.
2
1] Geballe Laboratory for Advanced Materials, Stanford University, 476 Lomita Mall, Stanford, California 94305, USA [2] Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305, USA.
3
1] Geballe Laboratory for Advanced Materials, Stanford University, 476 Lomita Mall, Stanford, California 94305, USA [2] Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, Würzburg D-97074, Germany.
4
Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, Würzburg D-97074, Germany.
5
Geballe Laboratory for Advanced Materials, Stanford University, 476 Lomita Mall, Stanford, California 94305, USA.
6
1] Geballe Laboratory for Advanced Materials, Stanford University, 476 Lomita Mall, Stanford, California 94305, USA [2] Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, USA [3] Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA.
7
1] Geballe Laboratory for Advanced Materials, Stanford University, 476 Lomita Mall, Stanford, California 94305, USA [2] Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, USA [3] Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305, USA.

Abstract

The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy, and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. This indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.

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