Measurement of the q-dependent static spin susceptibility χ’(q) in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.9}$

We report the temperature dependence of the q-dependent static electron spin susceptibility χ’(q) in a high-${\mathit{T}}_{\mathit{c}}$ superconductor ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.9}$ obtained by measuring the Gaussian component of ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ nuclear spin-spin relaxation rate 1/${\mathit{T}}_{2\mathit{G}}$. We employ the low-field NMR technique, and explain why this difficult technique is necessary for obtaining reliable results. It was found that χ’(q) satisfies a Curie-Weiss law at the corner of the Brillouin zone above ${\mathit{T}}_{\mathit{c}}$. Comparison with the spin-lattice relaxation rate 1/${\mathit{T}}_1$ showed little evidence for pseudogap behavior.