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

Nature communications

PubMedID: 26006728

Ma EY, Calvo MR, Wang J, Lian B, Mühlbauer M, Brüne C, Cui YT, Lai K, Kundhikanjana W, Yang Y, Baenninger M, König M, Ames C, Buhmann H, Leubner P, Molenkamp LW, Zhang SC, Goldhaber-Gordon D, Kelly MA, Shen ZX. Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry. Nat Commun. 2015;67252.
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.