Phonon and magnetic neutron scattering at 41 meV in YBa2Cu3O7.

We report inelastic neutron scattering measurements at excitation energies h̄v , 41 meV in YBa 2Cu 3O 7. We separate magnetic and phonon contributions to the scattering cross section by a detailed analysis of the momentum dependence of the scattered intensity. The previously reported broad peak around q ­ spya, pyad in the normal state can be entirely accounted for by a phonon which primarily involves vibrations of the in-plane oxygen. Magnetic scattering centered around 41 meV and q ­ spya, pyad appears in the superconducting state only. Theoretical implications of these findings are discussed.