Abstract
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.
Highlights
The premise of s± superconductivity in the multiband iron-based superconductors [1, 2], with a sign-changing order parameter between the electron-like and hole-like Fermi-surface sheets [2, 3, 4], has raised the question of the effect of atomic-scale point-like disorder on superconductivity in these materials [5, 6]
The likelihood of line nodes of the order parameter in isovalently doped BaFe2(As1−xPx)2 [32], LaFePO [29], and KFe2As2 [28, 30, 31] are indicative of a nodal s±– or a d-wave superconductivity [3, 4] in the first two and latter respective cases
The modification of the critical current density of Ba(Fe1−xCox)2As2 and BaFe2(As1−xPx)2 by electron irradiation demonstrates that the field–independent contribution to jc apparent in sub-T to T–fields is due to collective pinning by atomic-sized point defects
Summary
The premise of s± superconductivity in the multiband iron-based superconductors [1, 2], with a sign-changing order parameter between the electron-like and hole-like Fermi-surface sheets [2, 3, 4], has raised the question of the effect of atomic-scale point-like disorder on superconductivity in these materials [5, 6]. Disorder effect on exotic superconductivity in iron pnictides Given that the appearance of gap nodes in an s-wave superconductor does not imply symmetry breaking, indirect experiments yield, as yet, most insight into the order parameter structure Such experiments include the low temperature behaviour of the penetration depth [8, 9, 10, 11, 12, 13, 14, 27, 29, 32] and the thermal conductivity [30, 32, 35, 37] as probes of the low-energy quasi-particle density of states (QPDOS), and the sensitivity of the iron-based superconductors to quasi-particle scattering by homogeneous atomic-scale point-like disorder.
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