Chiral tunneling of topological states: towards the efficient generation   of spin current using spin-momentum locking
  We show that the interplay between chiral tunneling and spin-momentum locking of helical surface states leads to spin amplification and filtering in a 3D Topological Insulator (TI). Chiral tunneling across a TI pn junction allows normally incident electrons to transmit, while the rest are reflected with their spins flipped due to spin-momentum locking. The net result is that the spin current is enhanced while the dissipative charge current is simultaneously suppressed, leading to an extremely large, gate tunable spin to charge current ratio (~20) at the reflected end. At the transmitted end, the ratio stays close to one and the electrons are completely spin polarized. 
K. M. Masum Habib, Redwan N. Sajjad and Avik W. Ghosh
cond-mat.mes-hall