Electron irradiation of Co, Ni, and P-doped BaFe2As2–type iron-based superconductors

High energy electron irradiation is used to controllably introduce atomic-scale point defects into single crystalline Ba(Fe1?xCox)2As2, Ba(Fe1?xNix)2As2, and BaFe2(As1?xPx)2. The appearance of the collective pinning contribution to the critical current density in BaFe2(As1?xPx)2, and the magnitude of its enhancement in Ba(Fe1?xCox)2As2, conform with the hypothesis of quasi-particle scattering by Fe vacancies created by the irradiation. Whereas the insignificant modification of the temperature dependence of the superfluid density in Ba(Fe1?xCox)2As2 and Ba(Fe1?xNix)2As2 points to important native disorder present before the irradiation, the critical temperatures of these materials undergo a suppression equivalent to that observed in the much cleaner BaFe2(As1?xPx)2. This lends credence to the hypothesis of line nodes of the order parameter (at finite kz) in the former two materials.