| It is now generally accepted that the problem of high temperature superconductivity is due to strong correlations among electrons. It represents one of the major challenges in condensed matter physics. This work is a concentrated effort to create large single crystals of high temperature superconducting materials and to study quantitatively their magnetic excitation spectra using neutron scattering techniques. It will address the issues of the magnetic resonance, the normal state susceptibility, the superconducting spin gap and the even channel excitations in systems of various hole and Zn impurity concentrations. Findings on the magnetic resonance in the Bi2Sr2CaCu 2O8+δ and the latest measurements on the incommensurate fluctuations in the superconducting states in YBa2Cu3O 6.85 will also be reported. Collectively, these phenomena provide important information on the magnetism and bilayer interaction in these systems, and their role in the physics of the high Tc problem. |
