Magnetic Excitations in Superconducting YBa₂Cu₃O_6+x Crystals Studied by Neutron Inelastic Scattering

Abstract

Magnetic excitation spectra in single crystals of YBa₂Cu₃O_6+x with superconducting transition temperature T_c\simeq66 K (x\simeq0.75) and 90 K (x\simeq0.9) are reported. For excitation energies in the range 25–45 meV, a scan at fixed energy yields a single peak with a large q-width centered on the antiferromagnetic wave vector, (π,π), in agreement with the work of Rossat-Mignod and coworkers. However, in contrast to the results of the latter group, we have not observed, despite significant effort, any q-dependent magnetic scattering in either crystal at energies below ∼20 meV, even at temperatures far above T_c.