Spin Correlation and Superconductivity in High-TcOxides

Abstract

63Cu NQR and NMR and 170 NMR studies are presented for La.-rSrrCuO., YBa.Cu307 and TI.Ba.Cu06+Y· In the superconducting state, the T-dependence of the Knight shift has shown that the superconducting energy gap is larger in the Cu02 (2LI/ka Tc=4.4 -4.9) than the BCS prediction, being consistent with an s-wave model. In contrast, the T, result below Tc cannot be interpreted by a simple s-wave model. In the normal state, T,-' of Cu is strongly enhanced by antiferromagnetic (AF) spin correlation and its T-dependence is related to the T-dependence of the staggered suscep· tibility x Q( T) at the zone boundary. The large enhancement of x Q is remarkable for the superconducting compound, which is considered to play a key-role for the anomalous normal and superconducting properties in high- Tc oxides. The correlation between Tc and AF spin correlation is discussed.