High-T_c Superconductivity in Ln–Ba–Cu–O Systems (Ln=Lanthanide Atoms)

High-Tc superconductivity has been discovered for Ln-Ba-Cu-O systems with Ln=Lu, Yb, Tm, Er, Ho, Dy, Gd, Eu, Sm and Nd. The transition temperatures Tc are as high as that of the Y-Ba-Cu-O system, although almost all Ln atoms carry magnetic moments. The insensitivity of the Tc-values seems to be understood by the consideration of their structures, where the superconducting electrons are within the layers of Ba-Cu-O system sepeparated by the layers of Ln atoms.