On-Site Repulsion as the Source of Pairing in Carbon Nanotubes and   Intercalated Graphite
  We show that different non-conventional superconductors have one fundamental feature in common: pair eigenstates of the Hamiltonian are repulsion-free, the W=0 pairs. In extended Hubbard models, pairing can occur for resonable parameter values. For $(N,N)$ nanotubes the binding energy of the pair depends strongly on the filling and decreases towards a reduced but nonzero value for the graphite sheet $N \to \infty$. 
Enrico Perfetto, Gianluca Stefanucci and Michele Cini