Oxygen Phonon Branches in Detwinned YBa2Cu3O7
  We report results of inelastic neutron scattering measurements of phonon dispersions on a detwinned sample of YBaCu3O7 and compare them with model calculations. Plane oxygen bond stretching phonon branches disperse steeply downwards from the zone center in both the a and the b direction indicating a strong electron-phonon coupling. Half way to the zone boundary, the phonon peaks become ill-defined but we see no need to invoke unit cell doubling or charge stripe formation: lattice dynamical shell model calculations predict such behavior as a result of branch anticrossings. There were no observable superconductivity-related temperature effects on selected plane oxygen bond stretching modes measured on a twinned sample. 
D. Reznik, L. Pintschovius, W. Reichardt, Y. Endoh, H. Hiraka, J. M.   Tranquada, S. Tajima, H. Uchiyama, and T. Masui