Recent progress on neutron studies of YBa2Cu3O6+x

A review is given of recent developments in inelastic neutron scattering experiments on the high temperature superconductor YBa_2Cu_3O_7 and its antiferromagnetic precursor YBa_2Cu_3O_6.2. These include the detection of high energy “optical” spin waves and the determination of the full spin Hamiltonian in YBa_2Cu_3O_6.2, a detailed study of the 40 meV magnetic resonance peak in the superconducting state of YBa_2Cu_3O_7, and experiments on the effect of superconductivity on phonon lifetimes in YBa_2Cu_3O_7. This revised version was published online in August 2006 with corrections to the Cover Date.