Structure and superconductivity in LnNi2B2C: comparison of calculation and experiment

The experimental relation between the superconducting transition temperature (Tc) and lattice size for the lanthanide nickel borocarbides is clarified. The electronic density of states (DOS) at the Fermi energy is calculated by the LMTO method for selected non-magnetic lanthanides. The Tc and the DOS are both shown to scale in the same way with a structural parameter that characterizes the bond angle in the NiB4 tetrahedra. The results strongly support arguments that the suppression of superconductivity on going from smaller to larger lanthanides in the quaternary nickel borocarbides is structurally driven. A structure–Tc relationship of this type is unusual for intermetallic superconductors.