Density dependence of the energy of N Cooper pairs M. Combescot, T. Cren, M. Crouzeix and O. Betbeder-Matibet Eur. Phys. J. B, 80 1 (2011) 41-49 Published online: 09 March 2011 DOI: 10.1140/epjb/e2011-10943-2