We propose a method to determine the relative strength of Rashba and Dresselhaus spin-orbit interaction from transport measurements without the need of fitting parameters. To this end, we make use of the conductance anisotropy in narrow quantum wires with respect to the directions of an in-plane magnetic field, the quantum wire, and the crystal orientation. We support our proposal by numerical calculations of the conductance of quantum wires based on the Landauer formalism which show the applicability of the method to a wide range of parameters.

We consider the possibility to employ a quantum wire realized in a twodimensional electron gas (2DEG) as a spin ratchet. We show that a net spin current without accompanying net charge transport can be induced in the nonlinear regime by an unbiased external driving via an ac voltage applied between the contacts at the ends of the quantum wire. To achieve this we make use of the coupling of the electron spin to inhomogenous magnetic fields created by ferromagnetic stripes patterned on the semiconductor heterostructure that harbours the 2DEG. Using recursive Green function techniques we numerically study two different setups, consisting of one and two ferromagnetic stripes, respectively.

We demonstrate that the combined effect of a spatially periodic potential, lateral confinement, and spin-orbit interaction gives rise to a quantum ratchet mechanism for spin-polarized currents in two-dimensional coherent conductors. Upon adiabatic ac driving, in the absence of a net static bias, the system generates a directed spin current while the total charge current is zero. We analyze the underlying mechanism by employing symmetry properties of the scattering matrix and numerically verify the effect for different setups of ballistic conductors. The spin current direction can be changed upon tuning the Fermi energy or the strength of the Rashba spin-orbit coupling.

We calculate the electrically induced spin accumulation in diffusive systems due to both Rashba ͑with strength ␣͒ and Dresselhaus ͑with strength ␤͒ spin-orbit interaction. Using a diffusion equation approach we find that magnetoelectric effects disappear and that there is thus no spin accumulation when both interactions have the same strength, ␣ = Ϯ ␤. In thermodynamically large systems, the finite spin accumulation predicted by Chaplik, Entin, and Magarill ͓Physica E 13, 744 ͑2002͔͒ and by Trushin and Schliemann ͓Phys. Rev. B 75, 155323 ͑2007͔͒ is recovered an infinitesimally small distance away from the singular point ␣ = Ϯ ␤. We show however that the singularity is broadened and that the suppression of spin accumulation becomes physically relevant ͑i͒ in finite-sized systems of size L, ͑ii͒ in the presence of a cubic Dresselhaus interaction of strength ␥, or ͑iii͒ for finite-frequency measurements. We obtain the parametric range over which the magnetoelectric effect is suppressed in these three instances as ͑i͒ ͉␣͉ − ͉␤͉ Շ 1 / mL, ͑ii͒ ͉␣͉ − ͉␤͉ Շ ␥p F 2 , and ͑iii͒ ͉␣͉ − ͉␤͉ Շ ͱ / mp F ᐉ with ᐉ the elastic mean-free path and p F the Fermi momentum. We attribute the absence of spin accumulation close to ␣ = Ϯ ␤ to the underlying U͑1͒ symmetry. We illustrate and confirm our predictions numerically.