Universal pair-breaking in transition metal-substituted iron-pnictide superconductors

TL;DR

This study reveals a universal pair-breaking mechanism in transition metal-substituted iron-pnictide superconductors, establishing a critical scattering rate that limits their maximum transition temperature and constrains the superconducting gap structure.

Contribution

It demonstrates a universal pair-breaking rate across various 122 iron-based superconductors and quantifies the critical scattering rate limiting Tc.

Findings

A universal suppression rate of Tc with scattering rate.

A maximum Tc limit of approximately 26 K due to pair-breaking.

A critical scattering rate of 1.5x10^14 s^-1 for superconductivity suppression.

Abstract

The experimental transport scattering rate was determined for a wide range of optimally doped transition metal-substituted FeAs-based compounds with the ThCr2Si2 (122) crystal structure. The maximum transition temperature Tc for several Ba-, Sr-, and Ca-based 122 systems follows a universal rate of suppression with increasing scattering rate indicative of a common pair-breaking mechanism. Extraction of standard pair-breaking parameters puts a limit of \sim26 K on the maximum Tc for all transition metal-substituted 122 systems, in agreement with experimental observations, and sets a critical scattering rate of 1.5x10^14 s^-1 for the suppression of the superconducting phase. The observed critical scattering rate is much weaker than that expected for a sign-changing order parameter, providing important constraints on the nature of the superconducting gap in the 122 family of iron-based superconductors.