Effect of electron irradiation on superconductivity in isovalently substituted Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$

Single crystals of isovalently substituted Ba(Fe$_{1-x}$Ru$_{x}$)$_{2}% $As$_{2}$ were irradiated at $23$ K by $2.5$ MeV electrons with a total fluence up to $2\times10^{19}$ electrons per cm$^{2}$. The resistance was measured both in situ at $23$ K during irradiation, and as a function of temperature in a separate set-up, between the irradiation runs while the sample warmed to room temperature. We found that $\Delta\rho_{0}/\rho_{0}\approx0.2$ change in the residual resistivity, reached at the maximum irradiation dose, led to about a $\Delta T_{c}/T_{c0}\approx0.35$ decrease of $T_{c}$. This trend is universal in samples of different doping levels with different initial $T_{c0}$. The in-situ measurements also allowed us to understand the effects of room temperature annealing on the point-like defects induced by irradiation. The annealing results in a decrease of about a 20\% of the total increase in resistance achieved due to irradiation. However, residual 80\% remain stable at least one month after irradiation. We compare our results with theoretical predictions for different pairing scenarios, including extended $s_{\pm}$. Work in Ames was supported by the Department of Energy Office of Science, Basic Energy Sciences under Contract No. DE-AC02-O7CH11358.