Effect of Irradiation-Induced Disorder on the Conductivity and Critical Temperature of the Organic Superconductorκ−(BEDT−TTF)2Cu(SCN)2

We have introduced defects into clean samples of the organic superconductor $\kappa \mathrm{\text{−}}(\mathrm{BEDT}\mathrm{\text{−}}\mathrm{TTF}{)}_2\mathrm{Cu}(\mathrm{SCN}{)}_2$ in order to determine their effect on the temperature dependence of the interlayer conductivity $\sigma$ and the critical temperature $T_{\mathrm{c}}$. We find a violation of Matthiessen’s rule that can be explained by a model of $\sigma$ involving a defect-assisted interlayer channel which acts in parallel with the bandlike conductivity. We observe an unusual dependence of $T_{\mathrm{c}}$ on residual resistivity, inconsistent with the generalized Abrikosov-Gor’kov theory for an order parameter with a single component, providing an important constraint on models of the superconductivity in this material.