Ion-selective scattering studied by the variable-energy electron irradiation of Ba$_{0.2}$K$_{0.8}$Fe$_2$As$_2$ superconductor

TL;DR

This study uses variable-energy electron irradiation to induce and analyze non-magnetic disorder in a Ba$_{0.2}$K$_{0.8}$Fe$_2$As$_2$ superconductor, revealing defect creation primarily in the iron sublattice and its impact on superconductivity.

Contribution

It demonstrates the energy-dependent creation of defects in the iron sublattice and confirms its dominant role in scattering within iron-based superconductors.

Findings

Resistivity increases linearly with irradiation fluence at all energies.

Defect creation peaks at energies below 1.5 MeV.

Superconducting $T_c$ decreases monotonically with increasing energy.

Abstract

Low-temperature variable-energy electron irradiation was used to induce non-magnetic disorder in a single crystal of hole-doped iron-based superconductor, Ba$_{1-x}$K$_x$Fe$_2$As$_2$, $x=$0.80. To avoid systematic errors, the beam energy was adjusted non-consequently for five values between 1.0 and 2.5 MeV, whence sample resistance was measured in-situ at 22 K. For all energies, the resistivity raises linearly with the irradiation fluence suggesting the creation of uncorrelated dilute point-like disorder (confirmed by simulations). The rate of the resistivity increase peaks at energies below 1.5 MeV. Comparison with calculated partial cross-sections points to the predominant creation of defects in the iron sublattice. Simultaneously, superconducting $T_c$, measured separately between the irradiation runs, is monotonically suppressed as expected since it depends on the total scattering rate, hence total cross-section, which is a monotonically increasing function of energy. Our work confirms experimentally an often-made assumption of the dominant role of the iron sub-lattice in iron-based superconductors.