Enhancement of $T_{c}$ by disorder in underdoped iron pnictides

TL;DR

This paper demonstrates that in underdoped iron pnictides, disorder can increase the superconducting transition temperature $T_{c}$ by suppressing magnetic order, challenging the conventional view that disorder always reduces $T_{c}$ in these materials.

Contribution

It reveals that disorder can enhance $T_{c}$ in underdoped iron pnictides by suppressing magnetic order, providing new insights into $s^{+-}$ pairing mechanisms.

Findings

Disorder increases $T_{c}$ in the coexistence regime.

Suppression of magnetic order by disorder can outweigh pair-breaking effects.

Results support $s^{+-}$ pairing in iron pnictides.

Abstract

We analyze how disorder affects the transition temperature $T_{c}$ of the $s^{+-}$superconducting state in the iron pnictides. The conventional wisdom is that $T_{c}$ should rapidly decrease with increasing inter-band non-magnetic impurity scattering, but we show that this behavior holds only in the overdoped region of the phase diagram. In the underdoped regime, where superconductivity emerges from a pre-existing magnetic state, disorder gives rise to two competing effects: breaking of the Cooper pairs, which tends to reduce $T_{c}$, and suppression of the itinerant magnetic order, which tends to bring $T_{c}$ up. We show that for a wide range of parameters the second effect wins, leading to an increase of $T_{c}$ with disorder in the coexistence state. Our results explain several recent experimental findings and provide another evidence for $s^{+-}$-pairing in the iron pnictides.