Fluctuation conductivity and possible pseudogap state in FeAs-based superconductor EuFeAsO0.85F0.15

Abstract

The study of excess conductivity in the textured polycrystalline FeAs-based superconductor EuFeAsO0.85F0.15 () prepared by the solid state synthesis is reported for the first time. The analysis has been performed within the local pair (LP) model based on the assumption of the LPs formation in cuprate high-Tc superconductors (cuprates) below the pseudogap (PG) temperature . Similarly to the cuprates, near is adequately described by the 3D term of the Aslamasov–Larkin (AL) theory but the range of the 3D-AL fluctuations, , is relatively short. Above the crossover temperature is described by the 2D Maki–Thompson (MT) fluctuation term of the Hikami–Larkin theory. But enhanced 2D-MT fluctuation contribution being typical for the magnetic superconductors is observed. Within the LP model the PG parameter, , was determined for the first time. It is shown that demonstrates the narrow maximum at followed by the descending linear length down to . Observed small , enlarged 2D and linear are considered to be the evidence of the enhanced magnetic interaction in EuFeAsO0.85F0.15. Importantly, the slop of the linear and its length are found to be the same as it is revealed for SmFeAsO0.85. The results suggest both the similarity of the magnetic interaction processes in different Fe-pnictides and applicability of the LP model to the analysis even in magnetic superconductors.