Weak localization and phase interference due to spin-orbit interaction in metal-doped carbon nanotubes

Electrode atoms are slightly diffused, with only about 5% volume ratio, into the top end of multiwalled carbon nanotubes ~MWNT’s!, standing in nanopores of porous alumina membranes. Diffusion of light-mass materials ~carbon and aluminum! leads to weak localization in the Altshuler-Aronov-Spivak ~AAS! oscillations, which is qualitatively consistent with previous works on MWNT’s. In contrast, we find that diffusion of heavy materials ~gold and platinum! changes this weak localization into an antilocalization in the MWNT bulk. This effect is only observable when electrons are injected through the diffusion region and undergo a p-phase shift in their electron waves, caused by polarized injection of spin-flipped electrons due to spin-orbit interaction in the diffusion region of the MWNT bulk.