Electron-phonon coupling, Coulomb pseudo potential .mu.* and physical properties of C60 compounds.

Gunnarsson O., Antropov V.P., Fink J., Golden M.S., Knupfer M., Liechtenstein A.I., Merkel M., Rainer D., Zwicknagl G.

Max-Planck Institut Festkoerperforschung, Stuttgart, D-70506, Germany

The authors present ab initio calcns. of the phonon frequencies and electron phonon-coupling for the intra mol. phonons of Ag and Hg symmetry. They obtain a coupling .lambda. .apprx. 0.6 - 0.7 for K3C60 and Rb3C60 and est. the Coulomb pseudopotential .mu.*. Within the RPA the screened, but unrenormalized, .mu. .apprx. 0.4. To est. the renormalization due to retardation effects, the inter band scattering matrix elements are calcd. and found to be important. Within the framework where ladder diagrams in the screened interaction are summed the renormalization effects are important. Vertex corrections are, however, important, and for a two-band model, the authors show that renormalization effects actually are small. Assuming that this also applies to C60 they obtain .mu.* .apprx. 0.4. To explain the supercond. it is assumed that the electron-phonon coupling is somewhat (factor 1.3) larger than the calcd. value. The photoemission spectrum for doped C60 compds. is studied, including phonon and plasmon satellites. The anomalously broad spectrum for K3C60 and Rb3C60 can be explained by the presence of plasmon satellites. The phonon contribution to the T-dependent resistivity is studied. A satisfactory description of the exptl. results is obtained and some limits on the electron-phonon coupling are established.

NATO ASI Ser., Ser. C, 8 443, 1994.

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