THEORY OF THE SPIN DYNAMICS IN THE CUPRATES - COMPARISON OF THE LASRCUO AND YBACUO FAMILIES

We summarize magnetic data in the copper oxides and emphasize the cont rasting behavior seen in neutron experiments on the two cuprates: LaSr CuO and YBaCuO. We attribute the different q-dependence in the magneti c structure factor S(q, w) to differences in the Fermi surface geometr y, obtained in band structure approaches and (for the YBaCuO system) c orroborated by photoemission experiments. Using a large Coulomb U, Fer mi liquid based scheme, we present results for the q, w and temperatur e dependence of the neutron cross section in both cuprate families at various hole concentrations. These calculations compare favorably with experiment. NMR measurements on the Cu site are shown to be consisten t with these neutron data, as well as with our calculations. However, within the constraints of the standard transfer hyperfine model, the r elaxation on the oxygen site is difficult to reconcile with neutron da ta. The implications of d-wave symmetry are explored and it is argued that both normal and superconducting magnetic data pose some problems for the simple d-wave pairing scenario.