Suppression of superconductivity by spin fluctuations in iron-based superconductors

TL;DR

This paper investigates how spin fluctuations in iron-based superconductors can both promote and suppress superconductivity, revealing a self-restraint mechanism due to the repulsive nature of the pairing interaction.

Contribution

It demonstrates that spin fluctuations inherently contain a component that suppresses superconductivity, highlighting a fundamental self-restraint in the pairing mechanism.

Findings

Spin fluctuations can suppress superconductivity through phase frustration.

Superconductivity can still emerge at lower temperatures despite suppression.

The suppression is linked to the repulsive pairing interaction in the spin-fluctuation mechanism.

Abstract

We study the superconducting instability mediated by spin fluctuations in the Eliashberg theory for a minimal two-band model of iron-based superconductors. While antiferromagnetic spin fluctuations can drive superconductivity (SC) as is well established, we find that spin fluctuations necessarily contain a contribution to suppress SC even though SC can eventually occur at lower temperatures. This self-restraint effect stems from a general feature of the spin-fluctuation mechanism, namely the repulsive pairing interaction, which leads to phase frustration of the pairing gap and consequently the suppression of SC.