A photoemission study of the metallic ground state of potassium-doped C60 peapods

We report on the doping dependence of the electronic structure of the valence band of mats of C-60-filled single wall carbon nanotubes (C-60 peapods) studied by high resolution photoemission spectroscopy. In the pristine state, the bundles consist of approximately one third metallic tubes which are Tomonaga-Luttinger liquids (TLL) and thus show a power law scaling of the density of states near the Fermi level. The power law scaling factor of the pristine peapods is hardly increased compared to that of single-walled carbon nanotubes (SWCNT). Upon doping we find a complex doping behavior and charge distribution between the electronic states of the SWCNT and the encaged C-60 chains. Close to the Fermi level this has consequences on the doping induced crossover from a TLL to a conventional Fermi liquid which is found at a higher charge transfer as compared to intercalated SWCNT bundles.