Orbital symmetry and superconductivity in carbides and borocarbides

Abstract

The recent discovery of superconductivity in the quaternary borocarbides LnNi2B2C has generated a lot of interest in similar borocarbides, both for their potential applications as well as for elucidating mechanisms of electron transport. However, superconductivity has long been recognized in various analogous lanthanide dicarbides. Both structures contain molecular anionic fragments, (C-C) n − and (B-C-B) n −, respectively, that interact with a metal framework. This contribution examines the orbital interactions within this class of extended solids, and discusses how orbital symmetry arguments provide a model for electronic instabilities in the superconducting carbides and borocarbides.