Structural and electronic properties of LaFeAsO$_{0.85}$F$_{0.15}$ superconductor modified under neutron irradiation

TL;DR

This study investigates how neutron irradiation affects the crystal structure and electronic properties of LaFeAsO$_{0.85}$F$_{0.15}$, revealing suppression of superconductivity and changes in electronic behavior.

Contribution

It provides new insights into how atomic disorder from neutron irradiation modifies the structural and electronic properties of this superconductor.

Findings

Neutron irradiation causes anisotropic lattice expansion and increased Fe-As distance.

Superconductivity is suppressed with increased neutron fluence.

In highly disordered samples, electronic behavior follows the Korringa law.

Abstract

The effect of atomic disorder induced by neutron irradiation on the crystal structure and electronic states near $E_F$ of the lightly overdoped LaFeAsO$_{0.85}$F$_{0.15}$ ($T_c=21K$) was studied by X-ray diffraction and $^{75}$As NMR. The irradiation of the polycrystalline sample by "moderate" neutron fluence of $\Phi=(0;0.5;1.6)\cdot10^{19}cm^{-2}$ at $T=50^{\circ}C$ leads to the suppression of superconductivity. It is shown that neutron irradiation produces an anisotropic expansion of the tetragonal lattice almost due to an increase of the Fe-As distance. A partial loss of the 2D character of the FeAs layer is accompanied with a suppression of the gap-like feature in temperature dependence of the spin susceptibility. In the most disordered state the $^{75}$As spin-lattice relaxation rate follows the Korringa law $^{75}T_1^{-1} \sim T$, the thermal behavior being typical for an isotropic motion of the conducting electrons.