Non-linear elasto-Hall measurements in iron-based superconductors

It is well established that a rotational symmetry breaking electronic nematic phase is ubiquitous in the phase diagrams of iron-based superconductors and that anisotropic strain is a uniquely powerful in-situ probe of electronic anisotropy in these systems. In addition to the long-held belief that magnetic/nematic fluctuations are essential to understanding the pairing mechanism of the high T_c superconductivity, they also drastically modify the normal state properties, evidenced by non-Fermi liquid behavior and strongly temperature dependent transport coefficients. In this work, we present the observation of the non-linear elasto-Hall effect in Co doped and P doped BaFe2As2. Our measurement reveals a large quadratic term of the Hall coefficient as a function of B2g anisotropic strain. For the optimally doped composition, the nonlinear elasto-resistivity diverges as temperature decreases. Combined with elastoresistivity, our result provides crucial insight into how nematicity and nematic fluctuations couple to conducting electrons.