First-principles electronic structure of superconductor Ca 4Al 2O 6Fe 2P 2: Comparison with LaFePO and Ca 4Al 2O 6Fe 2As 2

Abstract

We investigate the electronic structures of iron-based superconductors having perovskite-like blocking layers, Ca 4Al 2O 6Fe 2P 2 and Ca 4Al 2O 6Fe 2As 2, from first principles. Ca 4Al 2O 6Fe 2P 2 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 between their band structures and measured transition temperatures of superconductivity is discussed. The number of Fermi surfaces in Ca 4Al 2O 6Fe 2P 2 is also different from that in Ca 4Al 2O 6Fe 2As 2, 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 difference in pnictogen height. We then analyze the alloying effect on the electronic structure of Ca 4Al 2O 6Fe 2AsP. It is found that this electronic structure is similar to those of Ca 4Al 2O 6Fe 2P 2 and Ca 4Al 2O 6Fe 2As 2 with average crystal structures, though Ca 4Al 2O 6Fe 2AsP contains pnictogen height disorder. We calculate the generalized susceptibility for Ca 4Al 2O 6Fe 2(As 1-xP x)2 and clarify the factors determining its tendency. © 2012 The Physical Society of Japan. © 2012 The Physical Society of Japan.