Superconductivity-Induced Anomalies in c-Axis Polarized Phonon Modes of YBa_2Cu_3O_7 Studied by Neutron Inelastic Scattering

Abstract

Superconductivity-induced phonon anomalies have beenstudied by inelastic neutron scattering for c-axis polarized modes ina single crystal of YBa₂Cu₃O₇. A mode with B_2u symmetry, which has out-of-phase motions of crystallographically distinct O(2)and O(3) atoms within a CuO₂ plane, apparently exhibits a frequencydecrease and a narrowing of the profile width with onset of thesuperconductivity, while a mode which has in-phase motions of theseoxygens with respect to Cu atoms within the CuO₂ plane does notshow an appreciable anomaly. The (x²-y²)-like symmetry of thesuperconducting order parameter is suggested by considering recenttheoretical arguments.