RECENT NEUTRON-SCATTERING RESULTS ON HIGH-TEMPERATURE SUPERCONDUCTORS

Triple-axis spectrometry has been used to determine the magnetic excitations in YBa2Cu3O7. Polarized measurements at 10 K show the scattering consists of a peak near 40 meV while 100 K data show a mostly flat continuum. At 10 K the 40-meV peak is found to be sharp in energy and anisotropic in momentum occupying a square portion of the Cu-O reciprocal lattice plane. The temperature dependence of the scattering is identical at the square side and corner. Polarized measurements show that the small background scattering observed at 100 K disappears below the superconducting transition. Resonant absorption measurements made to examine the Cu phonons show no observable changes in the phonons at the superconducting transition.