Phonon density of states inPb2Sr2(Ca,Y)Cu3O8

Abstract

The phonon density of states of the high-$T_c$ superconductor ${\mathrm{Pb}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Ca}}_{0.5}$ ${\mathrm{Y}}_{0.5}$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_8$ has been measured by the neutron time-of-flight technique. Comparison with the undoped nonsuperconducting compound ${\mathrm{Pb}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{YCu}}_3$ ${\mathrm{O}}_8$ shows small differences near 35 and 67 meV. Available lattice-dynamical results suggest the relevant spectral regions correspond to Sr and O(3) bond-bending modes in the first case, and O(1), O(2) bond-stretching modes in the second case. The results are discussed in the light of comparable results on other high-$T_c$ superconductors.