Controlling factors of Tc dome structure in 1111-type iron arsenide superconductors

Abstract

We investigated the effects of phosphorus substitution on the shape of the Tc(x) dome in 1111-type SmFeAs1−yPyO1−xHx (0<x<0.5). Hydride ion substitution of oxide sites (O2−→H−) exerts a chemical pressure effect, i.e., a structural reduction of the Pn−Fe−Pn angle α (Pn=P,As) and also dopes electrons into the FePn layer to induce superconductivity. Isovalent phosphorus substitution (P3−→As3−) can induce only a chemical pressure effect, i.e., an increase of α for La substitution of Sm sites. As y increases from 0.0 to 0.5, the single Tc dome gradually splits into two domes, similar to those of LaFeAsO1−xHx with a Tc valley at x≈0.16. We found that the Tc valley is located around (x,α)≈(0.16,113°) for both of the SmFeAs1−yPyO1−xHx and LaFeAsO1−xHx series, irrespective of changes in the Pn anion and Ln cation species. This result suggests that suppression of Tc leads to the emergence of a Tc valley when both the shape of FePn4 tetrahedra represented by α and electron-doping level of x meet the above criterion in 1111-type iron oxypnictide superconductors.

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