Raman-scattering study ofR2CuO4(R=Pr, Nd, Sm, and Gd)

Abstract

For ${\mathrm{Gd}}_2$ ${\mathrm{CuO}}_4$, a symmetry-forbidden phonon for the tetragonal T’ structure is observed. This shows that oxygen in the ${\mathrm{CuO}}_2$ plane is locally distorted along the plane. Such distortion has not been observed for other T’-type superconductors. The normal-mode calculation shows that the correlation between the ${\mathrm{CuO}}_2$ plane and R-O layers increases with decreasing ionic radius. The increased three-dimensional character and the appearance of the distortion of O in the ${\mathrm{CuO}}_2$ plane along the a axis are useful experimental results that help clarify the mechanism that causes the disappearance of superconductivity for Gd.