Localized and Delocalized Charge Transport in Single-Wall Carbon-Nanotube Mats

We measured the complex dielectric constant in mats of single-wall carbon nanotubes between 2.7 K and 300 K up to 0.5 THz. The data are well understood in a Drude approach with a negligible temperature dependence of the plasma frequency ${\ensuremath{\omega}}_{p}$ and scattering time $\ensuremath{\tau}$ with an additional contribution of localized charges. The dielectric properties resemble those of the best ``metallic'' polypyrroles and polyanilines. The absence of metallic islands makes the mats a relevant piece in the puzzle of the interpretation of $\ensuremath{\tau}$ and ${\ensuremath{\omega}}_{p}$ in these polymers.