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 electronic 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-tin 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)) becomes small enough to make the system nonferromagnetic and then superconducting. 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 right 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 approximation indicates that the superconductivity in YNi2B2C can be properly described by the conventional phonon mechanism.