Electrical Detection of Spin-Momentum Locking

One of the unique properties of topological insulators is that of spin-momentum locking — the spin of the surface state is locked at a right angle to the carrier momentum, and this characteristic has been probed by photoemission measurements on cleaved samples in ultrahigh vacuum. In principal, inducing a net carrier momentum (by applying a bias current, for example) should spontaneously generate a net spin polarization. However, attempts at accessing the spin-momentum locking of the surface states by electrical means, i.e., generating such spin polarization and directly sampling the current-induced spin polarization, have not been successful, and these effects have not been demonstrated.

Here, in collaboration with Dr. Jonker of the Naval Research Lab, by utilizing a ferromagnet/tunnel barrier contact that is intrinsically sensitive to surface/interface spins, we demonstrate for the first time that one can directly generate a net spin accumulation with a simple bias current, and directly detect the current-induced spin polarization of the surface spin due to spin-momentum locking, where its projection onto the detector contact magnetization is manifested as a voltage.

Published in Nature Nanotechnology:

“Electrical detection of charge-current-induced spin polarization due to spin-momentum locking in Bi2Se3“, C. H. Li, M. J. van’t Erve, J. T. Robinson, Y. Liu, L. Li and B. T. Jonker, Nat. Nanotechnology 9, 218 (2014).