Sample-specific and ensemble-averaged magnetoconductance of individual single-wall carbon nanotubes

We discuss magnetotransport measurements on individual single-wall carbon nanotubes (SWNTs) with low contact resistance, performed as a function of temperature and gate voltage. We find that the application of a magnetic field perpendicular to the tube axis results in a large magnetoconductance of the order of e2/h at low temperature. We demonstrate that this magnetoconductance consists of a sample-specific and of an ensemble-averaged contribution, both of which decrease with increasing temperature. The observed behavior resembles very closely the behavior of more conventional multichannel mesoscopic wires, exhibiting universal conductance fluctuations and weak localization. A theoretical analysis of our experiments will enable us to reach a deeper understanding of phase-coherent one-dimensional electronic motion in SWNTs.