Raman scattering spectra of a superconductingPb2Sr2Y0.75Ca0.25Cu3O8+δsingle crystal

Abstract

Raman Spectra of a superconducting ${\mathrm{Pb}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Y}}_{0.75}$ ${\mathrm{Ca}}_{0.25}$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{8+\mathrm{\delta }}$ single crystal ($T_c$≊20 K) have been measured at different temperatures between 10 and 300 K. Through their polarization properties, the Raman features observed at 90, 150, 240, 430, 480, and 570 ${\mathrm{cm}}^{\mathrm{-}1}$ are identified as the six $A_g$ modes, while the mode positioned at 325 ${\mathrm{cm}}^{\mathrm{-}1}$ has $B_{1g}$ symmetry. The components of the Raman tensor for these phonons have been determined. The frequencies and assignments obtained here correlate well with lattice-dynamical calculations for ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$. The possible effect of the distortion of the oxygen atom from the ideal rocksalt-type structure of the PbO layers is discussed.