Nematicity and structural strain: a tight connection in Fe-based superconductors.

In the present work, the role of microstrain developing in the temperature range above the structural transition in Fe-based superconductors is analysed in depth. Reviewing the results obtained from different compositions, a similar behaviour emerges in all cases. In particular, using an accurate diffraction line broadening analysis it is demonstrated that the tetragonal-to-orthorhombic structural transition occurring on cooling is anticipated by a symmetry breaking developing on the local scale in the tetragonal plane. The increase in microstrain with decreasing temperature in the stability field of the tetragonal phase qualitatively mirrors the development of anisotropy measured in some physical properties, a behaviour ascribed to nematicity. These results demonstrate the tight and delicate interplay correlating structural features on the local scale with transport and magnetic properties.