Electronic structure and properties of vacancy-ordered YBa 2Cu 3O 6.5: Chain versus plane Fermi surfaces in YBa 2Cu 3O 7-δ

Abstract

Results of local density calculations of the electronic structure for vacancy-ordered YBa 2Cu 3O 6.5 using the highly precise full-potential linearized augmented-plane-wave (FLAPW) method are presented. For a model structure of the vacancy-ordering in YBa 2Cu 3O 6.5 with a “full-and empty-chain” configuration in the Cu(1) chain plane, detailed analyses of energy bands, density of states, Fermi surface, and electron-phonon interaction parameters are made and compared with results for YBa 2Cu 3O 7 and YBa 2Cu 3O 6. The 2D dpσ Cu(2) plane bands crossing E F are found to be insensitive to the oxygen stoichiometry or ordering in the Cu(1) chain; on the other hand, the formation of the ordered CuO chains in the Cu(1) plane is crucial in the determination of the chain electronic structure near E F. Thus, it is shown that both the ordering of oxygens (i.e., formation of chains) in the Cu(1) plane as well as the oxygen content (i.e., δ) are important in understanding the band-filling of the 2D dpσ bands and the observed metallic behavior in YBa 2Cu 3O 7-δ, where the CuO chains play the roles not only as a charge reservoir but also as a. metallic chain. We also present the calculated FS in the “vacancy-ordered” YBa 2Cu 3O 6.5, which agrees with a recent photoemission experiment.