Determination of temperature-dependent atomic displacements in the Ca10Ir4As8(Fe2As2)5 superconductor with a metallic spacer layer

We have used the combination of Fe K-edge and Ir L3-edge x-ray absorption measurements as a function of temperature to investigate local atomic displacements in the newly discovered Ca10Ir4As8(Fe2As2)5 superconducting system. We find relatively relaxed Fe-Fe atomic pair correlations with large displacements in the FeAs4 tetrahedra, revealed by Fe K-edge extended x-ray absorption fine structure (EXAFS) analysis. Similarly, the temperature dependence of Ir L3-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 Ca10Ir4As8(Fe2As2)5 system.