Correlation between linear resistivity and $T_c$ in the Bechgaard salts and the pnictide superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$

TL;DR

This study finds a linear resistivity component in Bechgaard salts that correlates with superconducting temperature and suggests antiferromagnetic fluctuations are key to pairing, with similar behavior observed in iron-pnictides.

Contribution

It demonstrates a universal correlation between linear resistivity and $T_c$ in both organic and pnictide superconductors, linking spin fluctuations to superconductivity.

Findings

Linear resistivity coefficient scales with $T_c$ in Bechgaard salts.

Similar resistivity behavior observed in iron-pnictide superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$.

Antiferromagnetic spin fluctuations are likely involved in pairing mechanisms.

Abstract

The quasi-1D organic Bechgaard salt (TMTSF)$_2$PF$_6$ displays spin-density-wave (SDW) order and superconductivity in close proximity in the temperature-pressure phase diagram. We have measured its normal-state electrical resistivity $\rho_a(T)$ as a function of temperature and pressure, in the $T \to 0$ limit. At the critical pressure where SDW order disappears, $\rho_a(T) \propto T$ down to the lowest measured temperature (0.1 K). With increasing pressure, $\rho_a(T)$ acquires a curvature that is well described by $\rho_a(T) = \rho_0 + AT + BT^2$, where the strength of the linear term, measured by the $A$ coefficient, is found to scale with the superconducting transition temperature $T_c$. This correlation between $A$ and $T_c$ strongly suggests that scattering and pairing in (TMTSF)$_2$PF$_6$ have a common origin, most likely rooted in the antiferromagnetic spin fluctuations associated with SDW order. Analysis of published resistivity data on the iron-pnictide superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ reveals a detailed similarity with (TMTSF)$_2$PF$_6$, suggesting that antiferromagnetic fluctuations play a similar role in the pnictides.