Superconductivity and electronic structure of perovskite MgCNi₃

The electronic structure, stability, electron-phonon coupling, and superconductivity of the nonoxide perovskite MgCNi₃ are studied using density functional calculations. The band structure is dominated by a Ni d derived density of states peak just below the Fermi energy, which leads to a moderate Stoner enhancement, placing MgCNi₃ in the range where spin fluctuations may noticeably affect transport, specific heat, and superconductivity, providing a mechanism for reconciling various measures of the coupling λ. Strong electron-phonon interactions are found for the octahedral rotation mode and may exist for other bond angle bending modes. The Fermi surface contains nearly canceling hole and electron sheets that give unusual behavior of transport quantities particularly the thermopower. The results are discussed in relation to the superconductivity of MgCNi₃.