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We discuss the interplay of superconductivity and strong correlations taking place when the narrow-band electron-phonon superconductors such as A3C60 are chemically expanded to approach and surpass the Mott metal-insulator transition. The theoretical scenario is addressed by means of Dynamical Mean Field Theory within an orbitally degenerate Hubbard model incorporating a singlet attraction mimicking unretarded phonon pairing. The theoretical phase diagram as a function of the intramolecular repulsion U is close to that of actual materials, with a bell shaped superconducting region preceding the Mott transition for increasing cell volume (increasing repulsion). Properties of expanded fulleride superconductors that are predicted by this model to be anomalous include: (i) a pseudogap in the normal phase; (ii) gain of kinetic energy and of Drude weight at the onset of superconductivity, as in high Tc cuprates; (iii) spin susceptibility and specific heat jumps not especially large despite the incipient Mott transition; (iv) two different energy scales governing the renormalized single particle dispersion, electronic entropy and specific heat jump. These findings, discussed in the light of existing and foreseeable experiments, suggest that expanded fullerides are members of a wider family of strongly correlated superconductors, together with cuprates and organic conductors.
References: M. Capone, M. Fabrizio, C. Castellani, and E. Tosatti, "Strongly Correlated Superconductivity" Science ,296}, 2364 (2002); M. Capone, M. Fabrizio, C. Castellani, and E. Tosatti,"Strongly Correlated Superconductivity and Pseudogap Phase near a multi-band Mott Insulator", Phys. Rev. Lett.93} 047001 (2004). M. Capone, M. Fabrizio, C.Castellani, E.Tosatti, "Unconventional Superconducting Properties in Expanded Fullerides" to be published |
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