Superconductivity in rare earth cuprate perovskites

Superconducting cuprate perovskites isostructural with Ba₂YCu₃O₇ incorporating a variety of rare earth ions are reported. Resistivity and magnetic susceptibility measurements show transition temperatures in excess of 90K for several materials, including Nd, Sm, Gd, Dy, Ho, Er and Lu-containing phases. Interestingly, Ce and Tb, with a readily accessible 4+ state, form phases other than the defect perovskite which are not superconductors. However, Pr, which also has an accessible 4+ state, does give a nonsuperconducting defect perovskite isostructural with Ba₂YCu₃O₇. The observation of high temperature superconductivity in phases containing ions carrying magnetic moments is significant because it suggests that the magnetic moment on the rare earth ion interacts only weakly with the electrons making up the band crucial to superconductivity in these materials.