Stabilization of the quantum spin Hall effect by designed removal of time-reversal symmetry of edge states.

Department of Physics and Astronomy, California State University, Northridge, California 91330, USA(Dated: December 12, 2013)The quantum spin Hall (QSH) effect is known to be unstable to perturbations violating time-reversal symmetry. We show that creating a narrow ferromagnetic (FM) region near the edge of aQSH sample can push one of the counterpropagating edge states to the inner boundary of the FMregion, and leave the other at the outer boundary, without changing their spin polarizations andpropagation directions. Since the two edge states are spatially separated into different “lanes”, theQSH effect becomes robust against symmetry-breaking perturbations.