Local structural investigation ofSmFeAsO1 − xFx high temperature superconductors

Abstract

A strong revitalization of the field of high temperaturesuperconductivity (HTSC) has been induced recently by the discovery ofTC around 26 K in F-doped LaFeAsO iron pnictides. Starting from this discovery, a hugeamount of experimental data have been accumulated. This important corpus of resultswill allow the development of suitable theoretical models aimed at describingthe basic electronic structure properties and nature of superconducting states inthese fascinating new systems. A close correlation between structural features andphysical properties of the normal and superconducting states has already beendemonstrated in the current literature. Advanced theoretical models are also based onthe close correlation with structural properties and in particular with the Fe–Astetrahedral array. As for other complex materials, a deeper understanding of theirstructure–properties correlation requires a full knowledge of the atomic arrangementwithin the structure. Here we report an investigation of the local structure in theSmFeAsO1 − xFx system carried out by means of x-ray total scattering measurements and pair distributionfunction analysis. The results presented indicate that the local structure of theseHTSC significantly differs from the average structure determined by means oftraditional diffraction techniques, in particular the distribution of Fe–As bondlengths. In addition, a model for describing the observed discrepancies is presented.