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 discovered superconductor, is studied using self-consistent band-structure techniques. Analysis of the transformation of the band structure for the hypothetical series of graphite-primitive graphite-primitive graphitelike boron-intercalated boron, shows that the band structure of MgB2 is graphitelike, with pi bands falling deeper than in ordinary graphite. These bands possess a typically delocalized and metallic, as opposed to covalent, character. The in-plane sigma bands retain their two-dimensional (2D) covalent character, but exhibit a metallic hole-type conductivity. The coexistence of 2D covalent in-plane and three-dimensional (3D) metallic-type interlayer conducting 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 to conductivity.