Discovery of high temperature superconductivity in bulk La₃Ni₂O₇ under hydrostatic pressure has sparked new interest in understanding the interplay between structural and electronic changes in this family of superconductors. Due to the requirement of high pressures, however, experimental probes for direct atomic-scale structural characterization have been restricted. Hence, recent superconductivity in compressively strained La₃Ni₂O₇ thin films at ambient pressure provides a unique platform to investigate changes in the atomic structure at the highest spatial resolution.

Here, we use scanning transmission electron microscopy (STEM) to directly probe the structural changes as a function of varying epitaxial strain, from -2% to 2%, in La₃Ni₂O₇ thin films [L. Bhatt et al. Nature (2026)]. To isolate structural motifs for stabilizing superconductivity, we use the STEM technique of multislice electron ptychography (MEP) - providing highest resolution and interpretable contrast in both light and heavy atoms - to quantitatively identify La, Ni and O atomic positions. Precise measurements of Ni-planar O bond angles reveal lifting of crystallin symmetry when going from tensile to compressive strain, similar to what is observed in bulk upon compression. Quantitative atomic-scale analysis of annular dark-field images demonstrates the importance of in-plane compression for achieving superconductivity. Contrary to the thus-far prevailing understanding of bulk La₃Ni₂O₇, c-axis compression is not necessary in thin films. We further identify defects such as intergrowths and local variations in oxygen stoichiometry as potential pathways for improving superconducting transitions in these thin films.