Nuclear-spin-lattice relaxation-rate measurements in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$

Experimental details are given for NMR and NQR measurements of nuclear-spin-lattice relaxation rates for the planar copper and oxygen sites in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$. Enrichment of samples with ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$, alignment of powder samples, elimination of artifacts in relaxation-rate measurements, and the unusual aspects of weak magnetic-field experiments used to overcome an observed magnetic-field dependence in the rates are described. The role of fluxoids in the magnetic-field dependence of the relaxation rates is discussed. The relaxation rate data are shown to be inconsistent with a spin-singlet, orbital s-wave pairing state with an isotropic energy gap.