Analysis of electronic structure and charge density of the high-temperature superconductor YBa2Cu3O7

Abstract

Self-consistent linearized augmented plane wave (LAPW) method calculations of the band structure, density of states, Fermi surface, Coulomb potential, charge density, core-level shifts, and electron-phonon interaction are presented for Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/. The calculated Sommerfield parameter ..gamma.. is 4.35 mJ(mole Cu)/sup /minus/1/ K/sup /minus/2/, roughly about a factor of 2 smaller than experimentally deduced values of the enhanced value ..gamma.. = (1 + lambda)..gamma../sub 0/, suggesting that the Fermi surface mass enhancement is of the order of unity. The crystal charge density is best represented by overlapping spherical ionic densities when the Cu and O ions are assigned charges of +1.62 and -1.69, respectively, corresponding to about 0.3 holes per oxygen atom. Core-level energies for the inequivalent atoms differ by as much as 0.45 eV for Cu and 0.7 eV for O, amounts which may be detectable by core-level spectroscopies. These results provide important information on the character and magnitude of ionic contributions to bonding in these materials. Within the rigid muffin-tin approximation, calculated McMillan-Hopfield parameters yield estimates for the electron-phonon strength lambda that appear to be too small to account for the observed T/sub c/. We point out an unusual band of oxygen-derived chain states below, butmore » within 0.1 eV of, the Fermi level.« less