Anti-localization caused by small doping of heavy-mass impurity-atoms in carbon nanotubes and a novel spintronics device

Multi-walled carbon nanotubes (MWNTs), standing in nanoporous alumina membranes, are doped at one end by impurity atoms from electrode materials. Doping of the light-mass materials (carbon and aluminum) leads to weak localization in Altshuler–Aronov–Spivak oscillation, consistent with past reports. In contrast, we find that doping of heavy-mass materials (gold and platinum) at a volume ratio of only about 5% changes this weak localization to anti-localization. It is understood by a drastic change of the phase interference, caused by the polarized injection of spin-flipped electrons due to spin–orbit interaction in the diffusion region, in the bulk of the MWNTs. We also propose a novel spintronics (electron-wave phase switching) circuit using this effect.