  Formation of electronic nematicity is a common thread of unconventional
superconductors. In iron-based materials, the long-range nematic order is
revealed by the orthorhombic lattice distortion, which importance is a highly
controversial topic due the small magnitude of the distortion. Here, we study
the local crystal structure of FeSe and its interaction with electronic degrees
of freedom using ultrafast electron diffraction, x-ray pair distribution
function analysis, and transmission electron microscopy and find a significant
lattice response to local nematicity. The study demonstrates how local lattice
distortions, which exist even at temperatures above the nematic phase
transition, can be released by photoexcitation, leading to an enhancement of
the crystalline order. The observed local atomic structures and their
out-of-equilibrium behavior unravel a sophisticated coupling between the
lattice and nematic order parameter in FeSe.
