SPIN EXCITATIONS IN HIGH-TC CUPRATES

The results of theoretical studies on the spin excitations of the extended t - J model treated in the slave-boson mean field theory are briefly summarized and compared with the experimental results of neutron scattering and nuclear magnetic resonance both for LSCO and YBCO. It is found that there exists reasonable overall agreement between experiments and the theory, which predicts the dx2-y2 superconductivity. The remaining unresolved questions are identified and the possible resolutions for some of these are proposed.