Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMR

TL;DR

This paper provides microscopic evidence of ferromagnetic spin fluctuations in iron pnictide superconductors, revealing their competition with superconductivity and implications for understanding the variability of critical temperatures.

Contribution

It is the first to experimentally confirm ferromagnetic fluctuations in iron pnictides using NMR, highlighting their role in superconductivity.

Findings

FM spin correlations exist in both hole- and electron-doped BaFe2As2.

FM fluctuations compete with superconductivity.

These fluctuations influence the superconducting transition temperature.

Abstract

In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic (AFM) and in-plane ferromagnetic (FM) wavevectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using $^{75}$As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe$_2$As$_2$ families of iron-pnictide superconductors. These FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of $T_{\rm c}$ and the shape of the superconducting dome in these and other iron-pnictide families.