ELECTRONIC-STRUCTURE OF NI-BASED SUPERCONDUCTING QUATERNARY COMPOUNDS- YNI2B2X (X=B, C, N, AND O)

In order to explore a correlation between superconductivity and the el ectronic structure of Ni-based superconducting quaternary compounds, a systematic investigation of the electronic structures for YNi2B2X (X = B, C, N, and O) is carried out, by employing the linearized muffin-t in orbital band method. It is found that the Ni 3d density of states ( DOS) in YNi2B2C is broader than that in fcc Ni metal, and so N(E(F)) b ecomes small enough to make the system nonferromagnetic and then super conducting. A rigid-band-like shift of the Fermi level is observed as atom X varies. In the case of YNi2B2C, the Fermi level is located righ t at the van Hove-like singular DOS peak, which originates from saddle -point extremal band crossing GAMMA. This singular DOS peak at E(F) is expected to be related to the superconductivity observed in YNi2B2C. A crude estimate within the framework of the simple rigid-ion approxim ation indicates that the superconductivity in YNi2B2C can be properly described by the conventional phonon mechanism.