Application of the antiferromagnetic-Fermi-liquid theory to NMR experiments on YBa2Cu3O6.63

NMR experiments on the ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.63}$ material provide an important test of the antiferromagnetic-Fermi-liquid model for the spin-spin correlation function proposed by Millis, Monien, and Pines. We show that their theory provides a quantitative fit, with parameters determined from experiment, to the NMR experiments of Takigawa et al. on the Cu(2),O(2,3) nuclei, and of Alloul et al. on the Y nuclei in the ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.63}$ material. We find that the hyperfine couplings do not change in going from the ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ to the ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.63}$ material, whereas the antiferromagnetic correlation length is increased. We present results for the changes in relevant magnetic parameters brought about by reducing the oxygen content from ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ to ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.63}$ and discuss the implications of a small energy scale \ensuremath{\Elzxh}${\mathrm{\ensuremath{\omega}}}_{\mathrm{SF}}$${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{c}}$ emerging from the analysis of the NMR experiments. Our results support the proposal by Pines that the excitations in the normal state of superconducting Y-Ba-Cu-O are best described as those of an antiferromagnetic Fermi liquid and suggest that this description is equally applicable to other cuprate oxide superconductors.