Coexistence of covalent and metallic bonding in the boron intercalation superconductor MgB2 - art. no. 092503

Chemical bonding and electronic structure of MgB2, a boron-based newly disc overed superconductor, is studied using self-consistent band-structure tech niques. Analysis of the transformation of the band structure for the hypoth etical series of graphite-primitive graphite-primitive graphitelike boron-i ntercalated boron, shows that the band structure of MgB2 is graphitelike, w ith pi bands falling deeper than in ordinary graphite. These bands possess a typically delocalized and metallic, as opposed to covalent, character. Th e in-plane sigma bands retain their two-dimensional (2D) covalent character , but exhibit a metallic hole-type conductivity. The coexistence of 2D cova lent in-plane and three-dimensional (3D) metallic-type interlayer conductin g bands is a peculiar feature of MgB2 We analyze the 2D and 3D features of the band structure of MgB2 and related compounds, and their contributions t o conductivity.