# Effect of proton irradiation on the normal state low-energy excitations of Ba(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ superconductors

## TL;DR

This study investigates how 5.5 MeV proton irradiation affects the low-energy magnetic excitations and superconducting properties of Ba(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ iron-based superconductors, revealing enhanced spin fluctuations and magnetic correlations.

## Contribution

It provides new insights into the impact of proton-induced defects on magnetic excitations and nematic fluctuations in doped iron-based superconductors.

## Key findings

- Proton irradiation mildly suppresses Tc and increases residual resistivity.
- NMR spectra broaden significantly at low temperatures after irradiation.
- Irradiation enhances the energy barrier for low-energy spin fluctuations.

## Abstract

We present a \asnmr Nuclear Magnetic Resonance (NMR) and resistivity study of the effect of 5.5 MeV proton irradiation on the optimal electron doped ($x=$ 0.068) and overdoped ($x=$ 0.107) Ba(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ iron based superconductors. While the proton induced defects only mildly suppress the critical temperature and increase residual resistivity in both compositions, sizable broadening of the NMR spectra was observed in all the irradiated samples at low temperature. The effect is significantly stronger in the optimally doped sample where the Curie Weiss temperature dependence of the line width suggests the onset of ferromagnetic correlations coexisting with superconductivity at the nanoscale. 1/T$_2$ measurements revealed that the energy barrier characterizing the low energy spin fluctuations of these compounds is enhanced upon proton irradiation, suggesting that the defects are likely slowing down the fluctuations between ($0,\pi)$ and ($\pi$,0) nematic ground states.