The effect of irradiation-induced disorder on the conductivity and critical temperature of the organic superconductor $\kappa$-(BEDT-TTF)${}_2$Cu(SCN)${}_2$

Abstract

We have introduced defects into clean samples of the organic superconductor $\kappa$-(BEDT-TTF)${}_2$Cu(SCN)${}_2$ in order to determine their effect on the temperature dependence of the conductivity and the critical temperature $T_{\mathrm{c}}$. We find a violation of Matthiessen's rule that can be explained by a model of the conductivity involving a defect-assisted interlayer channel which acts in parallel with the band-like conductivity. We observe an unusual dependence of $T_{\mathrm{c}}$ on residual resistivity which is not consistent with the generalised Abrikosov-Gor'kov theory for an order parameter with a single component, providing an important constraint on models of the superconductivity in this material.