Effects of $c/a$ Anisotropy and Local Crystal Structure on Superconductivity in $A\mathrm{Fe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$ ($A$=Ba$_{1-y}$Sr$_y$, Sr$_{1-y}$Ca$_y$ and Eu)

TL;DR

This study examines how $c/a$ anisotropy and local crystal structure influence superconductivity in $A ext{Fe}_2( ext{As}_{1-x} ext{P}_x)_2$ systems, finding that Fermi surface topology changes do not affect $T_c$, but local structural parameters do.

Contribution

It reveals that structural anisotropy does not impact superconducting transition temperature, emphasizing the importance of local structural parameters like pnictogen height.

Findings

Structural anisotropy decreases with smaller $A$ ions.

Maximum $T_c$ remains nearly constant across different $A$ ions.

Fermi surface topology changes do not significantly affect $T_c$.

Abstract

We investigated the effects of $c/a$ anisotropy and local crystal structure on superconductivity (SC) in As/P solid solution systems, $A\mathrm{Fe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$ ($A$122P) with various $A$ ions. With decreasing $A$ site atomic size from $A$=Ba to Eu, the structural anisotropy decreases, and the rate of decreasing with $x$ also increases. The rapid narrowing of the region of antiferromagnetic composition ($x$) can be considered to be a result of this anisotropy change due mainly to the change in the Fermi surface (FS) nesting condition. By contrast, although the structural anisotropy systematically changes, the maximum $T_{\mathrm{c}}$ values are almost the same in all $A$122P systems except for Eu122P. These results indicate that the modification of the FS topology via the structural anisotropy does not affect SC. However local structural parameters, such as pnictogen height, are crucial for $T_{\mathrm{c}}$.