Local structural study of Fe_1.1Te using pair distribution function techniques

The link between electronic nematicity, magnetic and orbital order and their influence on high-T_c superconductivity is a highly controversial aspect in the physics of iron-based superconductors (FeSCs). It is believed that nematicity and superconductivity has a deep connection since optimal superconductivity occurs near nematic instabilities in FeSCs. Fe_1+yTe are promising candidates to understand the mechanism of superconductivity in the family of Fe-based superconductors. Here, we used the neutron pair distribution function (PDF) techniques to study the local structure of Fe_1.1Te above and below the structural transition temperature. We observed the first order transition from paramagnetic to commensurate antiferromagnetic ordering at 75 K corresponding to a tetragonal P4/nmm to monoclinic P21/m transition around 70 K. By tracking the monoclinicity parameter we observe the local scale distortions of the tetragonal and monoclinic structure in a typical range of 1-2 nm. These spatially limited distortions represent fluctuating nematic order which suggests the ubiquity of nematic fluctuations in iron-based superconductors. Our results agree well with the recent local structure study on FeSe and (Sr, Na)Fe₂As₂ which reveal the presence of short range orthorhombic distortions.