Impurity Effect on Superconducting Properties in Molecular Substituted Organic Superconductor $\kappa$-(ET)$_2$Cu(NCS)$_2$

TL;DR

This study investigates how substituting molecules in the organic superconductor $$-(ET)$_2$Cu(NCS)$_2$ affects its superconducting properties, revealing that impurity substitution decreases transition temperature and alters magnetic penetration depth.

Contribution

It provides new insights into impurity effects on organic superconductors by quantifying changes in transition temperature and magnetic properties due to molecular substitution.

Findings

Superconducting transition temperature decreases with impurity substitution.

In-plane magnetic penetration depth increases with substitution.

Reduction in effective pinning correlates with decreased condensation energy.

Abstract

We report an impurity effect in the organic superconductor $\kappa$-(ET)$_2$Cu(NCS)$_2$ by substitution of the ET molecule with an analogue, bis(methyleneditio)tetrathiafulvalene (MT). The superconducting transition temperature decreases with increasing substitution. The in-plane magnetic penetration depth is enhanced with substitution, which is quantitatively attributed to the decrease in the in-plane mean free path. The enhancement of the penetration depth can also explain the reduction of the effective pinning in terms of the condensation energy.