Influence of Defects Introduced by He+ Irradiation on Superconducting and Magnetotransport Properties of Ba(Fe0.94Co0.06As)2

The influence of 200 keV He+ ion irradiation on superconducting and magnetotransport properties of Ba(Fe0.94Co0.06As)2 films has been studied. It was shown that in the film under the corresponding irradiation conditions, mainly nonmagnetic defects are generated. It was found that suppression of superconductivity at increasing concentration of nonmagnetic defects is noticeably slower than expected from a simple theory assuming s± symmetry of the superconducting order parameter. The influence of defects on the magnetotransport properties has been analyzed. It was shown that the results of Hall measurements can be explained on the assumption that carriers are localized in the vicinity of radiation defect. The conclusion was made that the complete suppression of superconductivity occurs at a critical disorder in the system, which implies s++ symmetry of the order parameter. The results are explained basing on the assumption about electron pairing in real space on definite centers of pairing.