Superconductivity of Rb3C60: breakdown of the Migdal-Eliashberg theory E. Cappelluti, C. Grimaldi, L. Pietronero, S. Strässler and G. A. Ummarino Eur. Phys. J. B, 21 3 (2001) 383-391 Published online: 15 June 2001 DOI: 10.1007/PL00011123