Effect of Heavy-Ion Irradiation on Superconductivity in Single Crystals of Ba0.6K0.4Fe2As2 Pnictide Superconductor

TL;DR

This study investigates how heavy-ion irradiation affects the superconducting properties of Ba0.6K0.4Fe2As2 crystals, revealing that certain defect levels do not alter the superconducting gap, supporting an s+/- pairing state.

Contribution

It provides experimental evidence on the robustness of the superconducting gap and pairing symmetry under heavy-ion irradiation in Fe-based superconductors.

Findings

Superconducting gap remains unchanged at moderate irradiation levels.

High irradiation induces a T^2 power law behavior at low temperatures.

Superconducting transition sharpness is unaffected by irradiation.

Abstract

The London penetration depth was measured in optimally doped Ba0.6K0.4Fe2As2 crystals, with and without columnar defects produced by 1.4 GeV 208Pb irradiation. The low temperature behavior of unirradiated samples was consistent with a fully gapped superconducting state with a minimum energy gap delta_min/(k_B T_C) = 1. Similar gap values were observed for irradiation levels corresponding to mean column-column separations of 32 nm and 22 nm. At very high irradiation levels (column-column separation of 10 nm) a T^2 power law was observed below Tc/3, most likely due to elevated scattering. Neither the location nor the sharpness of the superconducting transition was affected by irradiation. The data provides evidence for an s+/- pairing state.