2004/09/22 by Deepa Kasinathan, K. -W. Lee, Kwan-Woo Lee +2
Materials Science · Physics and Astronomy · #Iron-based superconductors research #Physics of Superconductivity and Magnetism #Superconductivity in MgB2 and Alloys #cond-mat.mtrl-sci #cond-mat.supr-con
paper · pdf · doi:10.1016/j.physc.2005.05.002
published as Physica C 424, 116 (2005) · 8 pages, 8 figures
arxiv created 2004/09/22 · openalex publication_date 2005/06/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Heavy carbon doping of MgB2 is studied by first principles electronic structure studies of two types, an ordered supercell (Mg(B1-xCx)2,x=0.0833) and also the coherent potential approximation method that incorporates effects of B-C disorder. For the ordered model, the twofold degenerate σ-bands that are the basis of the high temperature superconductivity are split by 60 meV (i.e.7 meV/%C) and the σ Fermi cylinders contain 0.070 holes/cell, compared to 0.11 for MgB2. A virtual crystal treatment tends to overestimate the rate at which σ holes are filled by substitutional carbon. The coherent potential approximation (CPA) calculations give the same rate of band filling as the supercell method. The occupied local density of states of C is almost identical to that of B in the upper 2 eV of the valence bands, but in the range -8 eV to -2 eV, C has a considerably larger density of states. The calculations indicate that the σ Fermi surface cylinders pinch off at the zone center only above the maximum C concentration x ~ 0.10. These results indicate that Mg(B1-xCx)2 as well as Mg1-xAlxB2 is a good system in which to study the evolution of the unusual electron-phonon coupling character and strength as the crucial σ hole states are filled.