Magnetic-field dependence of planar copper and oxygen spin-lattice relaxation rates in the superconducting state of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$

The authors report nuclear spin-lattice relaxation rates, ${\mathit{W}}_1$, for planar copper and oxygen sites in the superconducting state of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$. These measurements were made with the static magnetic field along the c axis at a variety of static magnetic-field strengths. The data show that the relaxation rate of ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ depends on magnetic-field strength at low temperature and confirm a similar result for ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$. The importance of these measurements is that they give the zero-field limit necessary for comparison with theory. The weak-field data at low temperature for both copper and oxygen have a temperature dependence close to ${\mathit{T}}^3$, which is the result expected for spin-singlet, orbital d-wave pairing and does not seem compatible with orbital s-wave pairing.