Phonon density of states in YBa₂Cu₃O_x

We have investigated the room-temperature phonon density of states for several compounds in the YBa2Cu3Ox family using inelastic neutron scattering. Substantial variations are observed as a function of oxygen concentration, across the entire frequency range (0-90 meV). Near the high frequency cut-off, the spectral weight of the distribution shifts upwards by ≈ 10 meV, between x = 7.0 and x = 6.0. This shift is tentatively ascribed to enhanced electron-phonon coupling in the superconducting compound. Our interpretation is substantiated by complementary data on a non-superconducting Co-doped sample. © 1988.