Superconductivity in the LnNi2B2C intermetallics via boron A1g phonons

Abstract The superconducting properties of the lanthanide LnNi 2 B 2 C phases are attributed to an electron-phonon mechanism in which high frequency boron a 1g optical phonons dynamically modulate the tetrahedral NiB 4 bond angles. We identify a key energy-band feature within the NiBC s-p manifold whose position relative to E F is particularly sensitive to the NiB 4 tetrahedral geometry and which exhibits strong electron-phonon coupling. Favorable superconducting properties are expected for compounds where the NiB 4 tetrahedra are nearly “ideal” since this happens to optimize the alignment of this special s-p band with the Fermi level.