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

TL;DR

This study uses high energy electron irradiation to introduce point defects into various doped BaFe2As2 superconductors, revealing insights into their pinning mechanisms, disorder effects, and possible order parameter structures.

Contribution

It demonstrates how electron irradiation affects vortex pinning, superfluid density, and critical temperature, providing evidence for native disorder and order parameter nodal structure in these materials.

Findings

Collective pinning contribution appears in P-doped samples.

Superfluid density remains largely unchanged after irradiation.

Critical temperature suppression suggests line nodes in the order parameter.

Abstract

High energy electron irradiation is used to controllably introduce atomic-scale point defects into single crystalline Ba(Fe_1-xCo_x)_2As_2, Ba(Fe_1-xNi_x)_2As_2, and BaFe_2(As_1-xP_x)_2. The appearance of the collective pinning contribution to the critical current density in BaFe_2(As_1-xP_x)_2, and the magnitude of its enhancement in Ba(Fe_1-xCo_x)_2As_2, 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(Fe_1-xCo_x)_2As_2 and Ba(Fe_1-xNi_x)_2As_2 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 BaFe_2(As_1-xP_x)_2. This lends credence to the hypothesis of line nodes of the order parameter (at finite k_{z}) in the former two materials.