Hongbin Zhang, Frank Freimuth, Gustav Bihlmayer, Stefan Blügel, Yuriy Mokrousov
Using first principles methods, we investigate topological phase transitions as a function of exchange field in a Bi(111) bilayer. Evaluation of the spin Chern number for different magnitudes of the exchange field reveals that when the time reversal symmetry is broken by a small exchange field, the system keeps the properties of a topological insulator. After a metallic phase in the intermediate region, the quantum anomalous Hall phase with non-zero Chern number emerges at a sufficiently large exchange field. We analyze the phase diagram from the viewpoint of the evolution of the electronic structure, edge states and transport properties. In particular, we find that the significant spin polarization of the edge states is rather localized in space and can be controlled by an external exchange field.
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http://arxiv.org/abs/1203.5025
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