Probing nickelate superconductors at atomic scale: A STEM review

The discovery of nickelate superconductors, including doped infinite-layer (IL) nickelates RNiO₂ (R = La, Pr, Nd), layered square-planar nickelate Nd₆Ni₅O₁₂, and the Ruddlesden–Popper (RP) phase La₃Ni₂O₇, has spurred immense interest in fundamental research and potential applications. Scanning transmission electron microscopy (STEM) has proven crucial for understanding structure–property correlations in these diverse nickelate superconducting systems. In this review, we summarize the key findings from various modes of STEM, elucidating the mechanism of different nickelate superconductors. We also discuss future perspectives on emerging STEM techniques for unraveling the pairing mechanism in the “nickel age” of superconductivity.