Spin-fluctuation-induced superconductivity and normal-state properties of YBa2Cu3O7

Abstract

We have carried out strong-coupling calculations using the Eliashberg formalism for ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$. We consider the influence of potential impurity scattering on ${\mathit{T}}_{\mathit{c}}$. 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 ${\mathit{T}}_{\mathit{c}}$ 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 ${\mathit{T}}_{\mathit{c}}$. 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 ${\mathit{T}}_{\mathit{c}}$ to the details of the spin-fluctuation spectrum and hole concentration. When that spectrum is modified so that it is consistent with both NMR ${\mathit{T}}_1$ and ${\mathit{T}}_2$ measurements, a superconducting transition temperature of 90 K is obtained with a dimensionless coupling contant, λ<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 μΩ 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 ${\mathit{t}}_{\mathrm{\perp }}$ of 8 meV, the c-axis resistivity is found to be linear in temperature with a magnitude at 150 K of 2.5 mΩ cm.