Localization, Coulomb interactions, and electrical heating in single-wall carbon nanotubes/polymer composites

Low-field and high-field transport properties of carbon nanotubes/polymer composites are investigated for different tube fractions. Above the percolation threshold f(c)similar to0.33%, transport is due to hopping of localized charge carriers with a localization length xisimilar to10-30 nm. Coulomb interactions associated with a soft gap Delta(CG)similar to2.5 meV are present at low temperature close to f(c). We argue that it originates from the Coulomb charging energy effect which is partly screened by adjacent bundles. The high-field conductivity is described within an electrical heating scheme. All the results suggest that using composites close to the percolation threshold may be a way to access intrinsic properties of the nanotubes by experiments at a macroscopic scale.