First-principles theory of electron-spin fluctuation coupling and superconducting instabilities in iron selenide

TL;DR

This paper uses first-principles calculations to analyze how spin fluctuations in iron selenide influence superconducting instabilities, highlighting the competition between different spin fluctuation types and their impact on superconducting transition temperatures.

Contribution

It provides a detailed first-principles analysis of spin fluctuation coupling in iron selenide, elucidating the mechanisms behind superconducting instabilities and transition temperatures.

Findings

Strong antiferromagnetic spin fluctuations promote s_±-symmetry gaps.

Other spin fluctuations reduce the effective coupling constant.

Calculated coupling constants align with experimental transition temperatures.

Abstract

We present first-principles calculations of the coupling of quasiparticles to spin fluctuations in iron selenide and discuss which types of superconducting instabilities this coupling gives rise to. We find that strong antiferromagnetic stripe-phase spin fluctuations lead to large coupling constants for superconducting gaps with $s_\pm$-symmetry, but these coupling constants are significantly reduced by other spin fluctuations with small wave vectors. An accurate description of this competition and an inclusion of band structure and Stoner parameter renormalization effects lead to a value of the coupling constant for an $s_\pm$-symmetric gap which can produce a superconducting transition temperature consistent with experimental measurements.