Short-range nematic fluctuations in Sr1-xNaxFe2As2 superconductors

TL;DR

This study investigates short-range nematic fluctuations in Sr$_{1-x}$Na$_x$Fe$_2$As$_2$ superconductors using inelastic X-ray scattering, revealing how nematic susceptibility and correlation length vary with doping and their potential role in superconductivity.

Contribution

It provides the first detailed measurement of nematic susceptibility and correlation length in Sr$_{1-x}$Na$_x$Fe$_2$As$_2$, highlighting the importance of short-range nematic fluctuations in superconductivity.

Findings

Underdoped sample has a short nematic correlation length (~10 Å) and high nematic susceptibility.

Optimal doping reduces phonon softening, indicating decreased nematic correlation length and susceptibility.

Short-range nematic fluctuations may promote superconductivity in iron-based superconductors.

Abstract

Interactions between nematic fluctuations, magnetic order and superconductivity are central to the physics of iron-based superconductors. Here we report on in-plane transverse acoustic phonons in hole-doped Sr$_{1-x}$Na$_x$Fe$_2$As$_2$ measured via inelastic X-ray scattering, and extract both the nematic susceptibility and the nematic correlation length. By a self-contained method of analysis, for the underdoped ($x=0.36$) sample, which harbors a magnetically-ordered tetragonal phase, we find it hosts a short nematic correlation length $\xi$ ~ 10 $\AA$ and a large nematic susceptibility $\chi_{\rm nem}$. The optimal-doped ($x=0.55$) sample exhibits weaker phonon softening effects, indicative of both reduced $\xi$ and $\chi_{\rm nem}$. Our results suggest short-range nematic fluctuations may favor superconductivity, placing emphasis on the nematic correlation length for understanding the iron-based superconductors.