Symmetric and antisymmetric strain as continuous tuning parameters for electronic nematic order

Abstract

We report the separate response of the critical temperature of the nematic phase transition $T_{\mathrm{S}}$ to symmetric and antisymmetric strains for the prototypical underdoped iron pnictide Ba(Fe${}_{0.975}$Co${}_{0.025}$)${}_2$As${}_2$. This decomposition is achieved by comparing the response of $T_{\mathrm{S}}$ to uniaxial stress and hydrostatic pressure. In addition to quantifying the two distinct linear responses to symmetric strains, we find a quadratic variation of $T_{\mathrm{S}}$ as a response to antisymmetric strains ${\epsilon }_{{\mathrm{B}}_{1g}}$=$\frac{1}{2}$(${\epsilon }_{\mathrm{xx}}$-${\epsilon }_{\mathrm{yy}}$), exceeding the non linear response to symmetric strains by at least two orders of magnitude. These observations establish orthogonal antisymmetric strain as a powerful tuning parameter for nematic order.