Ballistic spin-polarized transport and Rashba spin precession in semiconductor nanowires

We present numerical calculations of the ballistic spin-transport properties of qunsi-one-dimensional wires in the presence of the spin-orbit (Rashba) interaction. A tight-binding analog of the Rashba Hamiltonian that models the Rashba effect is used. By varying the robustness of the Rashba coupling and the width of the wire, weak- and strong-coupling regimes are identified. Perfect electron-spin modulation is found for the former regime, regardless of the incident Fermi energy and mode number. In the latter however, the spin conductance has a strong energy dependence due to a nontrivial subband intermixing induced by the strong Rashba coupling. This would imply a strong suppression of the spin modulation at higher temperatures and source-drain voltages. The results may be of relevance for the implementation of quasi-one-dimensional spin-transistor devices.