Nematic fluctuations mediated superconductivity revealed by anisotropic strain in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$

TL;DR

This study uses anisotropic strain and Raman scattering to show that nematic fluctuations play a crucial role in mediating superconductivity in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, supporting theories of enhanced $T_c$ near nematic quantum criticality.

Contribution

It provides experimental evidence linking nematic fluctuations to superconductivity, demonstrating how strain affects nematic susceptibility and superconducting transition temperature.

Findings

Strain suppresses nematic susceptibility in BaFe$_2$As$_2$ as expected for an Ising order parameter.

In superconducting samples, suppression of nematic fluctuations correlates with decreased $T_c$.

Results support the role of nematic fluctuations in electron pairing and the proximity to a nematic quantum critical point.

Abstract

Anisotropic strain is an external field capable of selectively addressing the role of nematic fluctuations in promoting superconductivity. We demonstrate this using polarization-resolved elasto-Raman scattering to probe the evolution of nematic fluctuations under strain in the normal and superconducting states of the paradigmatic iron-based superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. In the non-superconducting parent compound BaFe$_2$As$_2$ we observe a strain-induced suppression of the nematic susceptibility which follows the expected behavior of an Ising order parameter under a symmetry breaking field. For the superconducting compound, the suppression of the nematic susceptibility correlates with the decrease of the superconducting critical temperature $T_c$. Our results indicate a significant contribution of nematic fluctuations to electron pairing and validate theoretical scenarios of enhanced $T_c$ near a nematic quantum critical point.