On the local inhomogeneities in the Fe-based chalcogenides and oxypnictides

 

N.L. Saini

Dipartimento di Fisica, Università di Roma gLa Sapienzah, P.le Aldo Moro 2, 00185 Roma, Italy

 

Diverging local structure and its implication on the superconductivity and magnetism of Fe-based supereconductors will be discussed. The case of Fe-based chalcogenides and oxypnictides will be considered. We have determined the local structure of FeSe1-xTex. Combination of Se and Fe K-edge absorption measurements has permitted to quantify the local inter-atomic distances and their mean square relative displacements. For example, the Fe-Se and Fe-Te bond lengths in the ternary system are found to be very different from the average crystallographic Fe-Se/Te distance, and almost identical to the Fe-Se and Fe-Te distances for the binary FeSe and FeTe systems, indicating distinct site occupation by the Se and Te atoms.  The results provide a clear evidence of local inhomogeneities and coexisting electronic components characterized by their local structural configurations in the FeSe1-xTex superconductors. The case of Fe-based REFeAsO oxypnictides is also considered, in which the RE L3-edge, As K and Fe K-edge x-ray absorption near-edge structure measurements, combined with multiple scattering calculations, suggest that order/disorder in the REO spacers and interlayer coupling should have important role in the superconductivity and itinerant magnetism.