Nonlinear uniaxial pressure dependence of the resistivity in Sr1−xBax Fe1.97Ni0.03As2**Project supported by the Science Fonds from the Ministry of Science and Technology of China (Grant Nos. 2017YFA0302903, 017YFA0303103, 2016YFA0300502, and 2015CB921302), the National Natural Science Foundation of China (Grant Nos. 11674406 and 11674372), the “Strategic Priority Research Program (B)” of the Chinese Academy of Sciences (Grant Nos. XDB07020300 and XDB07020200),

Abstract

Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain along the nematic direction and the normalized slope is thought to be associated with nematic susceptibility. Here we systematically studied the uniaxial pressure dependence of the resistivity in Sr1−xBaxFe1.97Ni0.03As2, where nonlinear behaviors are observed near the nematic transition temperature. We show that it can be well explained by the Landau theory for the second-order phase transitions considering that the external field is not zero. The effect of the coupling between the isotropic and nematic channels is shown to be negligible. Moreover, our results suggest that the nature of the magnetic and nematic transitions in Sr1 − xBaxFe2As2 is determined by the strength of the magnetic-elastic coupling.