Superconductivity-Induced Anomalies inc-Axis Polarized Phonon Modes of YBa2Cu3O7Studied by Neutron Inelastic Scattering

Abstract
Superconductivity-induced phonon anomalies have been studied by inelastic neutron scattering for c -axis polarized modes in a single crystal of YBa 2 Cu 3 O 7 . A mode with B 2u symmetry, which has out-of-phase motions of crystallographically distinct O(2) and O(3) atoms within a CuO 2 plane, apparently exhibits a frequency decrease and a narrowing of the profile width with onset of the superconductivity, while a mode which has in-phase motions of these oxygens with respect to Cu atoms within the CuO 2 plane does not show an appreciable anomaly. The ( x 2 - y 2 )-like symmetry of the superconducting order parameter is suggested by considering recent theoretical arguments.