The effects of doping, electron coherence, and electron correlation on the
transport properties of boron-doped multiwalled carbon nanotubes are studie
d. Substitutional boron lowers the Fermi level of the tubes and increases t
he number of participating conduction channels without introducing strong c
arrier scattering. From 300 to about 50 K, the tubes show metallic behavior
with weak electron-phonon coupling. At lower temperatures the resistance i
ncreases, and a zero-bias anomaly is observed. The magnetoresistance is now
negative indicating the importance of coherent back-scattering processes.
The coherence lengths are measured and dephasing is found to involve weakly
inelastic electron-electron collisions. The temperature dependence of the
resistance as well as the other low temperature observations can be account
ed for by one-dimensional weak-localization theory.