Transport in nanostructures and nanotubes

in two-dimensional honeycomb lattices, electronic states are described by Weyl's equation for a massless neutrino when each site is occupied by an electron on average. The system has a topological singularity at the origin k = 0 of the wave vector, giving rise to nontrivial Berry's phase when k is rotated around the origin. The singularity causes discrete jumps in the conductivity at the energy corresponding to k = 0 in honeycomb lattices and leads to the absence of backscattering and a perfect conductance in carbon nanotubes. (C) 2002 Elsevier Science B.V. All rights reserved.