We study mesoscopic spin Hall effect on the surface of a topological insulator with a step-function potential by using the McMillan method commonly used in the study of superconductor junctions. In the ballistic transport regime, we predict a giant spin polarization induced by a transverse electric current with parameter suitable to the topological insulator thin film ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. The spin polarization oscillates across the potential boundary with no confinement due to the Klein paradox, and should be observable in a spin resolved scanning tunneling microscope.

• Received 5 October 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.057205