Disorder-induced transverse delocalization in ropes of carbon nanotubes

A rope of carbon nanotubes consists in an array of parallel single wall nanotubes with nearly identical diameters. In most cases, the individual nanotubes within a rope have different helicities and 1/3 of them are metallic. In the absence of disorder within the tubes, the intertube electronic transfer is negligible because of the longitudinal wave vector mismatch between neighboring tubes of different helicities. The rope can then be considered as a number of parallel independent ballistic nanotubes. On the other hand, the presence of disorder within the tubes favors the intertube electronic transfer. This is first shown by using a very simple model wherein disorder is perturbatively treated as inspired by the work of Maarouf et al. [Phys. Rev. B 61, 11156 (2000)]. We then present numerical simulations of a tight binding model of a rope. A disorder induced transverse delocalization shows up as an increase (by typically 1 order of magnitude of the sensitivity to the transverse boundary conditions in the presence of small disorder). This is accompanied by an increase in the longitudinal localization length. The implications on the nature of electronic transport within a rope of carbon nanotubes are discussed.