Persistent Spin Helix Spin Polarizer

The persistent spin helix (PSH) occurs in 2-D nanosystems where the Rashba and Dresselhaus spin orbit interactions (RSOI/DSOI) are both present and of equal strength. The spin orbit interaction effective field experienced by the charge carriers due to RSOI and/or DSOI generally depends on the direction of the charge carrier momenta. The PSH is unique in that the direction of this effective magnetic field is independent of the momentum direction. We find that this results in the spin accumulation in a PSH system assuming only the PSH eigenspinor directions of ±(1, -1, 0) without any intermediate directions in between, when spin unpolarized electrons are injected into the PSH system. This can be explained by the accumulation of the spin up and spin down carriers about the PSH eigenspinor axis occurring in opposite directions, resulting in the the spin components perpendicular to ±(1, -1, 0) averaging to zero. In particular, the spin accumulation for an infinitely wide PSH segment connected to a narrow spin unpolarized source lead is partitioned between the (1, -1, 0) and (-1, 1, 0) directions along the upper and lower halves of the segment about the source lead-PSH interface. This partitioning of the spin accumulation motivates the proposal of a finite-sized PSH spin polarizer for generating ±(1, -1, 0) spin polarized currents. The spin polarization of the current can be optimized by reducing the length and increasing the width of the spin polarizer.