Electrical properties of single carbon nanotubes

Magnetoresistances of individual multiwall nanotubes have been measured at low temperatures in a four-probe configuration with low-ohmic contacts. A negative magnetoresistance is found which is in agreement with weak-localisation theory in one dimension. A large coherence length Lφ>200 nm is deduced at T=4.2 K. Measurements on different nanotubes show only minor variations in the value of the resistance and in its temperature dependence.