Coherent view on fullerenes: phonon-mediated correlated superconductivity and unusual normal state optical conductivity

Abstract

The wide range of experimental observations on fullerene superconductors can be understood if the Coulomb repulsion is included in addition to the electron-phonon interaction in the pairing kernel. These are characterized by lambda approximate to 0.7-0.8 and VCNF approximate to 0.3-0.4, where lambda is the dimensionless electron-phonon coupling constant, V-C the screened Coulomb repulsion, and N-F is the density of states at the Fermi level. This view of phonon-mediated correlated superconductivity is applied to the normal state fullerenes to check if an unusual feature observed in the normal state can also be understood within the view: the suppressed Drude weight and concomitant mid-infrared (MIR) peak in the optical conductivity. The Drude weight in the calculated optical conductivity is strongly suppressed., being similar to0.4 of the total intraband spectral weight, and is transferred to the MIR region around and above 0.06 eV which is somewhat less pronounced and much broader compared with the experimental observation by DeGiorgi et al.