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

Abstract

High energy electron irradiation is used to controllably introduce\natomic-scale point defects into single crystalline Ba(Fe_1-xCo_x)_2As_2,\nBa(Fe_1-xNi_x)_2As_2, and BaFe_2(As_1-xP_x)_2. The appearance of the collective\npinning contribution to the critical current density in BaFe_2(As_1-xP_x)_2,\nand the magnitude of its enhancement in Ba(Fe_1-xCo_x)_2As_2, conform with the\nhypothesis of quasi-particle scattering by Fe vacancies created by the\nirradiation. Whereas the insignificant modification of the temperature\ndependence of the superfluid density in Ba(Fe_1-xCo_x)_2As_2 and\nBa(Fe_1-xNi_x)_2As_2 points to important native disorder present before the\nirradiation, the critical temperatures of these materials undergo a suppression\nequivalent to that observed in the much cleaner BaFe_2(As_1-xP_x)_2. This lends\ncredence to the hypothesis of line nodes of the order parameter (at finite\nk_{z}) in the former two materials.\n