The Electronic Structure and Superconductivity of the High T sub c Copper Oxides.

The electronic structure of the new high T sub c copper oxides is discussed in terms of the conventional band picture and the localized orbital Mott-Hubbard picture. Values for the Coulomb interaction parameters entering the Hubbard model are extracted from a mapping of the model onto Density Functional results which yields an energy surface as a function of local charge fluctuations. Knowing the physical parameters appropriate for the copper-oxides, the nature of quasiparticles introduced by doping of the insulating parent compounds is deduced. Quasiparticle energies as measured by direct or inverse photoemission agree well with the calculations. In addition to this high energy scale, low energy magnetic excitations are obtained from using the calculated Hubbard parameters in cluster calculations. These, too compare well with experimental data. Finally, our calculated parameters indicate that the materials are intermediate between the extreme spin or charge fluctuation regimes. This places strong constraints on theories for high temperature superconductivity.