Local structural studies of Fe-based superconductors

In the framework of high temperature superconductors, the Fe-based systems are the rst magnetic materials that exhibit a critical temperature above 50 K. These systems are characterized by strong interplay between electronic, spin and lattice degrees of freedom and the macroscopic functional properties arise from the competitions between them. All the theoretically and experimental results point out on the diff iculty to separate the effects of disorder, doping and magnetism on the superconducting properties. The presence of multiple bands crossing the Fermi level makes the electronic structure very sensitive to the structural details, particulary to the changes on the local atomic arrangement in the Fe-Pn/Ch slabs. The aim of this work is to study the local structure and discuss possible implications on the electronic properties in the Fe-based superconductors. This has important implications, both in theoretical and in practical terms: a close relationship between structure and superconductivity, direct or indirect, places constraints on both the theoretical understanding of the pairing interaction and the promise of superconductors with higher TC values. The proposed sensitivity of electronic structure and/or magnetic interactions to the details of the internal structure of the Fe-As layers is likely relevant to unraveling this puzzle.