THEORY OF SPIN DYNAMICS IN YBA2CU3O7-DELTA - FERMIOLOGY EFFECTS

We reconcile the Fermi surface shape observed in photoemission experiments in YBa2Cu3O7-delta with recent neutron data. A peak at Q0 = (pi/a, pi/a) is found for delta=0.3 as a consequence of the q-dependent exchange interaction. The associated correlation length is roughly T independent, and the T, omega dependences of the peak height are found to be in reasonable agreement with experiment. We present predictions for the (even smaller) peak structure associated with the fully oxygenated system and demonstrate agreement with Cu NMR for both delta values.