Second-Order Spin Conductivity of Rashba Nanowires in a Longitudinal Magnetic Field

We show that a quasi-one-dimensional Rashba nanowire exhibits second-order spin conductivity. The nature of the Rashba effect is caused by the inversion asymmetry along the radial direction, and creates strong spin-momentum locking which determines which orientations of spin may be conducted down the longitudinal axis of the nanowire. The spin conductivity may be calculated in the diffusive regime using the Boltzmann-Transport Equation, driven by either an electric field or a thermal gradient applied along the long axis. While spin conductivity is possible for any non-zero value of the Rashba spin-orbit coupling strength, the strength of the Rashba effect is shown to cause peaks in the spin conductivity when tuned to a sufficient strength. Furthermore, under the influence of a longitudinal magnetic field the spin transport is affected by Aharonov-Bohm oscillations.