Lateral spin-orbit interaction and spin polarization in quantum point contacts

We study ballistic transport through semiconductor quantum point-contact systems under different confinement geometries and applied fields. In particular, we investigate how the lateral spin-orbit coupling, introduced by asymmetric lateral confinement potentials, affects the spin polarization of the current. We find that even in the absence of external magnetic fields, a variable nonzero spin polarization can be obtained by controlling the asymmetric shape of the confinement potential. These results suggest an approach to produce spin-polarized electron sources, and we study the dependence of this phenomenon on structural parameters and applied magnetic fields. This asymmetry-induced polarization provides also a plausible explanation of our recent observations of a 0.5 conductance plateau (in units of 2e(2)/h) in quantum point contacts made on InAs quantum-well structures. Although our estimates of the required spin-orbit interaction strength in these systems do not support this explanation, they likely play a role in the effects enhanced by electron-electron interactions.