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Direct transition between quantum spin Hall and ordinary insulating phases induced by spin-mixing tunneling in symplectic disordered quantum spin Hall systems

Research paper by Jie Lu, Mei Li

Indexed on: 22 Mar '17Published on: 22 Mar '17Published in: arXiv - Physics - Mesoscopic Systems and Quantum Hall Effect



Abstract

The disordered quantum spin Hall (QSH) systems with spin-mixing tunneling (SMT) at potential saddle points, which belong to the Wigner-Dyson symplectic class AII, are revisited in detail using an existing spin-directed quantum network model generalized from the Chalker-Coddington random network model. A new phase diagram is obtained in which the ordinary insulating (OI) phase fills the whole parameter space and the QSH state only survives on a line segment of the boundary where SMT is absent. Thus a direct transition from QSH to OI phases exists and is driven by the SMT since it induces backscattering between the Kramers doublets at the same edge and thus completely destroys them. To verify these results, finite-size analyses of the two-terminal conductance and normalized localization length of electrons are performed following standard numerical algorithms. Numerics clearly shows that once the SMT is switched on, neither marginal dissipationless channels nor bulk metallic states survive when the system size is large enough.