Electron irradiation of Co, Ni, and P-doped BaFe₂As ₂-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.