Coulomb interaction effects in spin-polarized transport

We study the effect of the electron-electron interaction on the transport of spin-polarized currents in metals and doped semiconductors in the diffusive regime. In addition to well-known screening effects, we identify two additional effects, which depend on many-body correlations and exchange and reduce the spin-diffusion constant. The first is the "spin Coulomb drag" an intrinsic friction mechanism which operates whenever the average velocities of up-spin and down-spin electrons differ. The second arises from the decrease in the longitudinal spin stiffness of an interacting electron gas relative to a noninteracting one. Both effects are studied in detail for both degenerate and nondegenerate carriers in metals and semiconductors, and various limiting cases are worked out analytically. The behavior of the spin-diffusion constant at and below a ferromagnetic transition temperature is also discussed.