High <i>T</i> _<i>c</i> electron doped Ca ₁₀ (Pt ₃ As ₈ )(Fe ₂ As ₂ ) ₅ and Ca ₁₀ (Pt ₄ As ₈ )(Fe ₂ As ₂ ) ₅ superconductors with skutterudite intermediary layers

TLDR

High‑Tc cuprates are thought to achieve their elevated transition temperatures through enhanced CuO₂ plane coupling mediated by heavy metal oxide intermediary layers, a mechanism that has not yet been tested in iron arsenide superconductors. The authors synthesized Ca₁₀(Pt₃As₈)(Fe₂As₂)₅ and Ca₁₀(Pt₄As₈)(Fe₂As₂)₅, finding that Pt‑substituted electron doping yields Tc values of 11 K and 26 K, respectively, and that the higher Tc in the 10‑4‑8 phase is attributed to stronger FeAs interlayer coupling via its metallic Pt₄As₈ layer rather than to As‑Fe‑As bond angles.

Abstract

It has been argued that the very high transition temperatures of the highest T(c) cuprate superconductors are facilitated by enhanced CuO(2) plane coupling through heavy metal oxide intermediary layers. Whether enhanced coupling through intermediary layers can also influence T(c) in the new high T(c) iron arsenide superconductors has never been tested due the lack of appropriate systems for study. Here we report the crystal structures and properties of two iron arsenide superconductors, Ca(10)(Pt(3)As(8))(Fe(2)As(2))(5) (the "10-3-8 phase") and Ca(10)(Pt(4)As(8))(Fe(2)As(2))(5) (the "10-4-8 phase"). Based on -Ca-(Pt(n)As(8))-Ca-Fe(2)As(2)- layer stacking, these are very similar compounds for which the most important differences lie in the structural and electronic characteristics of the intermediary platinum arsenide layers. Electron doping through partial substitution of Pt for Fe in the FeAs layers leads to T(c) of 11 K in the 10-3-8 phase and 26 K in the 10-4-8 phase. The often-cited empirical rule in the arsenide superconductor literature relating T(c) to As-Fe-As bond angles does not explain the observed differences in T(c) of the two phases; rather, comparison suggests the presence of stronger FeAs interlayer coupling in the 10-4-8 phase arising from the two-channel interlayer interactions and the metallic nature of its intermediary Pt(4)As(8) layer. The interlayer coupling is thus revealed as important in enhancing T(c) in the iron pnictide superconductors.