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

We have performed de transport and optical conductivity measurements on pur ified and potassium doped thick films of single walled carbon nanotubes. Th e pristine sample is characterized by a metallic (Drude) response of the op tical properties despite the non-metallic behavior in the de resistivity me asurements. Even though the spectral weight of the metallic component in th e electrodynamic response increases with doping, in agreement with the tren d 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 influe nces differently the non-metallic tube-tube contact regions and the intrins ic on-tube transport.