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

TL;DR

This study investigates how irradiation-induced defects affect the conductivity and critical temperature of the organic superconductor $2$-(BEDT-TTF)$_2$Cu(SCN)$_2$, revealing complex defect interactions and challenging existing theories.

Contribution

It introduces a defect model explaining conductivity changes and shows that $T_c$ dependence defies conventional Abrikosov-Gor'kov theory, offering new insights into superconductivity mechanisms.

Findings

Violation of Matthiessen's rule explained by defect-assisted interlayer conduction

Unusual $T_c$ dependence on residual resistivity inconsistent with single-component order parameter

Evidence of complex defect interactions affecting superconducting properties

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 $T_{\rm c}$. 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 $T_{\rm c}$ 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.