  We study spin-dependent diffusive transport in the presence of a tunable
spin-orbit (SO) interaction in a two-dimensional electron system. The spin
precession of an electron in the SO coupling field is expressed in terms of a
covariant curvature, affecting the quantum interference between different
electronic trajectories. Controlling this curvature field by modulating the SO
coupling strength and its gradients by, e.g., electric or elastic means, opens
intriguing possibilities for exploring spin-selective localization physics. In
particular, applying a weak magnetic field allows the control of the electron
localization independently for two spin directions, with the spin-quantization
axis that could be "engineered" by appropriate SO interaction gradients.
