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→∞.
@article{arxiv.cond-mat/0212122,
title = {On-Site Repulsion as the Source of Pairing in Carbon Nanotubes and Intercalated Graphite},
author = {Enrico Perfetto and Gianluca Stefanucci and Michele Cini},
journal= {arXiv preprint arXiv:cond-mat/0212122},
year = {2009}
}