Ubiquitous enhancement of nematic fluctuations across the phase diagram of iron based superconductors probed by the Nernst effect

TL;DR

This study demonstrates that nematic fluctuations, as measured by the Nernst effect, are enhanced across the entire phase diagram of iron-based superconductors and are correlated with superconductivity, suggesting a fostering role.

Contribution

The paper introduces the Nernst coefficient as a new probe for nematic fluctuations and shows its amplitude correlates with the superconducting dome in iron-based superconductors.

Findings

Nernst coefficient tracks the superconducting dome.

Nematic fluctuations are enhanced across the phase diagram.

Nematic fluctuations likely promote superconductivity.

Abstract

The role of nematic fluctuations for unconventional superconductivity has been subject of intense discussions for many years. In iron-based superconductors, the most established probe for electronic-nematic fluctuations, i.e. the elastoresistivity seems to imply that superconductivity is reinforced by electronic-nematic fluctuations, since the elastoresistivity amplitude peaks at or close to optimal $T_C$. However, on the over-doped side of the superconducting dome, the diminishing elastoresistivity suggests a negligible importance in the mechanism of superconductivity. Here we introduce the Nernst coefficient as a genuine probe for electronic nematic fluctuations, and we show that the amplitude of the Nernst coefficient tracks the superconducting dome of two prototype families of iron-based superconductors, namely Rh-doped $BaFe_{2}As_{2}$ and Co-doped $LaFeAsO$. Our data thus provide fresh evidence that in these systems nematic fluctuations foster the superconductivity throughout the phase diagram.