  We investigated spin-resolved electronic transport through a junction
composed of a nonmagnetic metal electrode and a zigzag carbon nanotube by means
of self-consistent Green's function method in the tight binding approximation
and the unrestricted Hartree-Fock approximation. Our results show that the
electric current can be spin-polarized if the coupling of the junction is weak.
Further calculations on spin-spin correlation and local density of states
reveal the existence of magnetic edge states in zigzag carbon nanotubes, which
is responsible for the observed spin-polarized current and can be controlled by
applying a gate voltage. We also studied the influence of the nearest-neighbor
Coulomb interaction and the junction coupling strength on the spin-polarization
of the current.
