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

We have performed de 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 de 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 de transport properties, there is a quantitative mismatch between the optical [sigma(1),(omega --> 0)] and de transport. Comparing the de and optical conductivity measurements we conclude that potassium doping influences differently the non-metallic tube-tube contact regions and the intrinsic on-tube transport.