Localization in carbon nanotubes within a tight-binding model

We analyze the influence of defects on conductance, density of states, and localization in (Nₐ,Nₐ) armchair carbon nanotubes within a tight-binding model. Using the transfer-matrix method, we calculate the reflection (related to the conductance) from a sequence of defects and relate its energy dependence near the Fermi level to the appearance of a quasibound state. This state is also seen in the density of states and in the energy dependence of the quasiparticle lifetime. We compute the localization length ξ(ω) as a function of energy {ω}. Comparison of ξ(0) with the mean free path lmfp in the limit of small defect concentration c and small defect strength E leads to a simple approximate relation ξ(0)≈3lmfp=3×3aNₐt²/2cE² $(t$--- hopping integral, a--- lattice constant).