Effect of nonmagnetic defects on superconducting and transport properties of Ba(Fe1- x Co x As)2 high- T c superconductors

The effect of nonmagnetic defects on superconducting and transport properties of Ba(Fe_0.94Co_0.06As)₂ films is studied for obtaining information on the symmetry type of the order parameter for superconducting pnictides. Such defects are generated in the film by irradiation by He⁺ ions with an energy of 200 keV. It is found that a decrease in superconducting transition temperature T_c upon an increase in the concentration of nonmagnetic defects in this compound occurs much more slowly than predicted in the model assuming s^±-wave symmetry of the order parameter. Joint analysis of the influence of nonmagnetic defects on the superconducting and magnetotransport properties of such films leads to the conclusion that superconductivity is completely suppressed in them after critical disorder is attained, which assumes the s⁺⁺-wave symmetry.