ANISOTROPIC S-WAVE GAP AND NUCLEAR-MAGNETIC-RESONANCE IN HIGH-TEMPERATURE SUPERCONDUCTORS

The Knight shift and the nuclear magnetic relaxation rates W(perpendic ular-to)63, W(parallel-to)63, and W(parallel-to)17 are calculated for temperatures below the superconducting transition temperature of the h igh-temperature cuprate superconductors; the superscripts refer to the Cu-63 and the O-17 nuclei while the subscripts refer to the direction of the magnetic field with respect to the CuO layers. The calculation s are based on a recently proposed interlayer tunneling mechanism of s uperconductivity in these materials. In general, the results are consi stent with experiments even though the superconducting gap respects th e full point-group symmetry of the lattice (anisotropic s wave); the a nisotropy of the magnitude of the gap is an essential element.