Electronic correlations in graphite and carbon nanotubes from Auger spectroscopy

We have determined the screened on-site Coulomb repulsion in graphite and single wall carbon nanotubes by measuring their Auger spectra and performing a theoretical analysis based on an extended Cini-Sawatzky approach [Solid State Commun. 24, 681 (1977); Phys. Rev. Lett. 39, 504 (1977)], where only one fit parameter is employed. The experimental line shape is very well reproduced by the theory, and this allows us to determine the value of the screened on-site repulsion between 2p states, which is found to be 2.1 eV in graphite and 4.6 eV in nanotubes. The latter is robust by varying the nanotube radius from 1 to 2 nm.