SPIN-FLUCTUATION-INDUCED SUPERCONDUCTIVITY AND NORMAL-STATE PROPERTIES OF YBA2CU3O7

We have carried out strong-coupling calculations using the Eliashberg formalism for YBa2Cu3O7. We consider the influence of potential impurity scattering on T(c). We find that, as the strength of the impurity potential increases, the unitary limit is reached comparatively quickly. In this (unitary) limit, the influence of isotropic impurity scattering on T(c) is relatively weak. We show, with the aid of a simple model to describe the disruption of the local magnetic order brought about by the substitution of Zn, that the latter has a strong influence on T(c). We consider the competition between antiferromagnetic and superconducting instabilities and find that, for our model parameters, the instability to a superconducting state always comes first. Next, we examine the sensitivity of our results for T(c) to the details of the spin-fluctuation spectrum and hole concentration. When that spectrum is modified so that it is consistent with both NMR T1 and T2 measurements, a superconducting transition temperature of 90 K is obtained with a dimensionless coupling contant, lambda < 1/2. Strong-coupling calculations of the normal state, using these latter parameters and including vertex corrections, yield an in-plane resistivity which varies linearly with temperature, with a magnitude at 100 K of 20 muOMEGA cm, and, with minor changes in parameters, a frequency dependence of the optical conductivity in quantitative agreement with experiment for energies < 50 meV. With an interlayer hopping t(perpendicular-to) of 8 meV, the c-axis resistivity is found to be linear in temperature with a magnitude at 150 K of 2.5 mOMEGA cm.