We report the observation of a nonlinear elastoresistivity response for the prototypical underdoped iron pnictide $\mathrm{Ba}{\left({\mathrm{Fe}}_{0.975}{\mathrm{Co}}_{0.025}\right)}_2{\mathrm{As}}_2$. 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.

中文翻译：

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铁基超导体向列相变附近对称（A1g）非线性弹性弹性的临界散度

我们报告了典型的掺杂不足的铁肽的非线性弹性反应的观察结果 $巴{（{铁}_{0.975}{\mathrm{有限公司}}_{0.025}）}_{\mathrm{2个}}{\mathrm{作为}}_{\mathrm{2个}}$。我们的测量结果表明，各向同性中有一个较大的二次项（${\mathrm{一个}}_{\mathrm{1个}G}$）纯剪切产生的电子响应（${乙}_{\mathrm{2个}G}$） 拉紧。冷却到结构相变时该量的差异反映了向列磁化率的温度依赖性。该观察结果表明，向列波动甚至在确定该化合物家族的各向同性性质中也起着重要作用。