First-principles Electronic Structure of Superconductor Ca₄Al₂O₆Fe₂P₂: Comparison with LaFePO and Ca₄Al₂O₆Fe₂As₂

Original · EN

We investigate the electronic structures of iron-based superconductors having perovskite-like blocking layers, %Ca₄Al₂O₆Fe₂(As₁₋ₓPₓ)₂ from first principles. Ca₄Al₂O₆Fe₂P₂ and Ca₄Al₂O₆Fe₂As₂ from first principles. Ca₄Al₂O₆Fe₂P₂ is found to have two hole-like Fermi surfaces around Γ, and one hole-like Fermi surface around M in the unfolded Brillouin zone. This is in contrast with LaFePO, where no Fermi surface is found around M. The relationship of their band structures and measured transition temperatures of superconductivity is discussed. The number of Fermi surfaces in Ca₄Al₂O₆Fe₂P₂ is also different from that of Ca₄Al₂O₆Fe₂As₂, in which only one Fermi surface is formed around Γ. Analysis using maximally localized Wannier functions clarifies that the differences between their band structures originate mainly from the pnictogen height. We then analyze the alloying effect on the electronic structure of Ca₄Al₂O₆Fe₂AsP. It is found that its electronic structure is similar to that of Ca₄Al₂O₆Fe₂P₂ and Ca₄Al₂O₆Fe₂As₂ with the average crystal structure, though Ca₄Al₂O₆Fe₂AsP contains the pnictogen height disorder. We calculate the generalized susceptibility for Ca₄Al₂O₆Fe₂(As₁₋ₓPₓ)₂ and clarify the factors determining its tendency.