Cu-O bond-stretching vibrations in YBa(2)Cu(3)0(7) studied by inelastic neutron scattering

Inelastic neutron experiments confirm the previously reported anomalous nature of the planar oxygen bond-stretching vibrations and furnish further details. It is shown that the frequency of the linear breathing mode is renormalized by 5 THz compared to insulating YBa2Cu3O6 Studies of the Cu1-apical O bond-stretching vibrations demonstrate that frequencies, line-widths and phonon intensities can well be understood within the framework of a harmonic lattice dynamical model. This rules out predictions of a double well potential and strong anharmonitity for this type of vibration.