Magnetoresistance of a quantum dot with spin-active interfaces

We study the zero-bias magnetoresistance (MR) of an interacting quantum dot connected to two ferromagnetic leads and capacitively coupled to a gate voltage source V-g. We investigate the effects of the spin-activity of the contacts between the dot and the leads by introducing an effective exchange field in an Anderson model. This spin-activity makes easier negative MR effects, and can even lead to a giant MR effect with a sign tunable with V-g. Assuming a twofold orbital degeneracy, our approach allows one to interpret in an interacting picture the MR(V-g) measured by S. Sahoo [Nature Phys. 1, 99 (2005)] in single wall carbon nanotubes with ferromagnetic contacts. If this experiment is repeated on a larger V-g range, we expect that the MR(V-g) oscillations are not regular like in the presently available data, due to Coulomb interactions.