Anisotropic s-wave gap and nuclear magnetic resonance in high-temperature superconductors.

Abstract

The Knight shift and the nuclear magnetic relaxation rates ${\mathit{W}}_{\mathrm{\ensuremath{\perp}}}^{63}$, ${\mathit{W}}_{\mathrm{\ensuremath{\parallel}}}^{63}$, and ${\mathit{W}}_{\mathrm{\ensuremath{\parallel}}}^{17}$ are calculated for temperatures below the superconducting transition temperature of the high-temperature cuprate superconductors; the superscripts refer to the $^{63}\mathrm{Cu}$ and the $^{17}\mathrm{O}$ nuclei while the subscripts refer to the direction of the magnetic field with respect to the CuO layers. The calculations are based on a recently proposed interlayer tunneling mechanism of superconductivity in these materials. In general, the results are consistent with experiments even though the superconducting gap respects the full point-group symmetry of the lattice (anisotropic s wave); the anisotropy of the magnitude of the gap is an essential element.