VIBRATIONAL ANOMALIES IN THE SUPERCONDUCTING COMPOUND LA1.85BA0.15CUO4

The barium-doped superconductor exhibits a linear fall in resistivity from room to liquid-nitrogen temperatures followed by a plateau to 35 K, at which point superconducting behavior begins. Evidence for the presence of a tetragonal to orthorhombic phase transition together with further subtle and anomalous structural instabilities in the barium-doped compound has been reported. To elucidate the correlations between the lattice vibrational and electronic behavior, we have undertaken neutron inelastic scattering experiments on the High Energy Transfer spectrometer at the ISIS facility of the Rutherford Appleton Laboratory, UK, using carefully prepared polycrystalline samples of both La//1//. //8//5Ba//0//. //1//5CuO//4 and La//2CuO//4. The experiments were performed over a range of temperatures between 12 K and 200 K. Here we report anomalous temperature dependence of modes centered at 10 mev and 20 mev respectively.