Optical and dc conductivity study of potassium-doped single-walled carbon nanotube films

We have performed dc transport and optical conductivity measurements on purified and potassium doped thick films of single walled carbon nanotubes. The pristine sample is characterized by a metallic (Drude) response of the optical properties despite the non-metallic behavior in the dc resistivity measurements. Even though the spectral weight of the metallic component in the electrodynamic response increases with doping, in agreement with the trend of the dc transport properties, there is a quantitative mismatch between the optical $[{\ensuremath{\sigma}}_{1}(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\omega}}0)]$ and dc transport. Comparing the dc and optical conductivity measurements we conclude that potassium doping influences differently the non-metallic tube-tube contact regions and the intrinsic on-tube transport.