Nonequilibrium dynamics of local lattice distortions in FeSe

The role of the lattice in unique properties of iron-based superconductors, such as electronic nematicity, is still unclear. This rises an interest in investigating the local structure modifications during the phase transitions in these materials. We report the study of the local crystal structure of FeSe and its connection to electronic nematicity using ultrafast electron diffraction, x-ray diffraction, and transmission electron microscopy. The study reveals the local distortions in form of iron dimers, ordered within nanometrer -sized domains. The observed nonequilibrium lattice dynamics implies sensitivity of the lattice distortions to the nematic order parameter.