Highly anisotropic anomaly in the dispersion of the copper-oxygen bond-bending phonon in superconducting YBa2Cu3O 7 from inelastic neutron scattering - M. Raichle; D. Reznik; D. Lamago; R. Heid; Y. Li; M. Bakr; C. Ulrich; V. Hinkov; K. Hradil; C.T. Lin; B. Keimer (Physical Review Letters, 2011)