Determination of temperature-dependent atomic displacements in theCa10Ir4As8(Fe2As2)5superconductor with a metallic spacer layer

Abstract

We have used the combination of Fe $K$-edge and Ir ${L}_{3}$-edge x-ray absorption measurements as a function of temperature to investigate local atomic displacements in the newly discovered ${\mathrm{Ca}}_{10}{\mathrm{Ir}}_{4}{\mathrm{As}}_{8}{({\mathrm{Fe}}_{2}{\mathrm{As}}_{2})}_{5}$ superconducting system. We find relatively relaxed Fe-Fe atomic pair correlations with large displacements in the ${\mathrm{FeAs}}_{4}$ tetrahedra, revealed by Fe $K$-edge extended x-ray absorption fine structure (EXAFS) analysis. Similarly, the temperature dependence of Ir ${L}_{3}$-edge EXAFS shows nanoscale disorder in the IrAs layer that should have a significant effect on the active FeAs-layer characteristics. Furthermore, x-ray absorption near edge structure data are presented to discuss the evolution of the unoccupied electronic states revealing the marginal role of spin-orbit coupling, while the interlayer interactions and disorder should be important for describing the physics of the ${\mathrm{Ca}}_{10}{\mathrm{Ir}}_{4}{\mathrm{As}}_{8}{({\mathrm{Fe}}_{2}{\mathrm{As}}_{2})}_{5}$ system.