First-principles study on iron-pnictide superconductors Ca(Fe1−xCox)2As2

The electronic structure, lattice dynamics, and electron–phonon (e–ph) coupling constants λ for the superconducting Ca(Fe1−xCox)2As2 (x=0.075, 0.1) are obtained by first-principles nonmagnetic calculations using norm-conserving pseudopotentials within virtual–crystal approximation treatment. Combined with the e–ph coupling constant λ for vicinity of collapsed tetragonal phase of CaFe2As2, we show that although the obtained λ cannot account for the high superconducting transition temperatures TC, they are almost a factor of two larger than that estimated in early calculations for that of vicinity of collapsed tetragonal phase of CaFe2As2. We confirm that superconductivity in Ca(Fe1−xCox)2As2 is not primarily phonon mediated. Nevertheless, the e–ph interactions are strong enough to be not negligible to investigate the superconductivity. Furthermore, we conjecture that Ca(Fe1−xMnx)2As2 or CaMn2As2 serial compounds may be potential new e–ph superconductors or unconventional manganese pnictide superconductors.