Critical divergence of the symmetric ($A_{1g}$) nonlinear elastoresistance near the nematic transition in an iron-based superconductor

TL;DR

This study uncovers a significant nonlinear elastoresistivity response in an iron-based superconductor, revealing how nematic fluctuations influence isotropic electronic properties near the structural phase transition.

Contribution

It demonstrates the divergence of the $A_{1g}$ nonlinear elastoresistance near the nematic transition, highlighting the role of nematic fluctuations in isotropic responses.

Findings

Large quadratic $A_{1g}$ response induced by shear strain

Divergence of response near structural transition

Nematic fluctuations influence isotropic properties

Abstract

We report the observation of a nonlinear elastoresistivity response for the prototypical underdoped iron pnictide Ba(Fe$_{0.975}$Co$_{0.025}$)$_2$As$_2$. Our measurements reveal a large quadratic term in the isotropic ($A_{1g}$) electronic response that was produced by a purely shear ($B_{2g}$) strain. The divergence of this quantity upon cooling towards the structural phase transition reflects the temperature dependence of the nematic susceptibility. This observation shows that nematic fluctuations play a significant role in determining even the isotropic properties of this family of compounds.