Separating spin and charge transport in single-wall carbon nanotubes

We demonstrate spin injection and detection in single wall carbon nanotubes using a four-terminal nonlocal geometry. This measurement geometry completely separates the charge and spin circuits. Hence all spurious magnetoresistance effects are eliminated and the measured signal is due to spin accumulation only. Combining our results with a theoretical model, we deduce a spin polarization at the contacts alpha(F) of approximately 25%. We show that the magnetoresistance changes measured in the conventional two-terminal geometry are only partly due to spin accumulation.