Topological insulators possess a symmetry-protected surface spin current, a property highly relevant to spintronics applications. This current arises from gapless spin-polarized surface states. Calculations show that these states can undergo drastic transformations with surface treatment, despite the overall symmetry-based constraints. Specifically, the single Dirac cone at the zone center for the surface states in Bi${}_2$Se${}_3$ (Bi${}_2$Te${}_3$) is transformed, upon hydrogen termination, into three Dirac cones at the zone boundary. This trifurcation enhances the surface spin polarization, but leaves the overall topological order invariant.

• Received 28 June 2011

DOI:https://doi.org/10.1103/PhysRevB.84.235414