SPIN EXCITATIONS IN HIGH-TC CUPRATES

The results of theoretical studies on the spin excitations of the exte nded t - J model treated in the slave-boson mean field theory are brie fly summarized and compared with the experimental results of neutron s cattering and nuclear magnetic resonance both for LSCO and YBCO. It is found that there exists reasonable overall agreement between experime nts and the theory, which predicts the dx2-y2 superconductivity. The r emaining unresolved questions are identified and the possible resoluti ons for some of these are proposed.