Orientation dependence of magneto-resistance behaviour in a carbon nanotube rope

The orientation dependence of magneto-resistance behaviour for a single-walled carbon nanotube (SWCN) rope is reported. A clear delineation of behaviours is observed between applying a magnetic field perpendicular or parallel to the rope axis. For a perpendicular field, monotonic negative magneto-resistance is observed due to two-dimensional weak localisation within the rope. By contrast, for a parallel field, complicated oscillatory behaviour is observed due to the Altshuler-Aronov-Spivak effect around closed electron trajectories on discrete cylinders within the SWCN rope. A dominant oscillatory mode can be identified which corresponds to closed paths around the outer circumference of the SWCN rope. However, due to the composite filamentary nature of the rope, the overall oscillatory behaviour is rather complicated and can be classified as universal conductance fluctuations. With a backgate voltage applied to the sample, Coulomb blockade peaks are observed in the transport current with additional peak structure superimposed due to resonant tunnelling. We find an interesting effect whereby these peaks are suppressed in the presence of a magnetic field. (C) 2002 Elsevier Science B.V. All rights reserved.