Octahedral Distortions at High‐Temperature Superconducting La₂CuO₄ Interfaces: Visualizing Jahn–Teller Effects

Abstract Tuning the octahedral network represents a promising route for achieving new properties and functionalities in perovskite‐based oxide heterostructures. One of the interface‐mediated phenomena occurring in complex oxides is the Jahn—Teller (JT) effect. With the purpose of investigating octahedral distortions at interfaces showing high‐temperature interface superconductivity, atomic layer‐by‐layer oxide molecular‐beam epitaxy grown bilayers consisting of three unit cells, overdoped metallic La_1.6M_0.4CuO₄, and three unit cells undoped insulating La₂CuO₄, where M represents a divalent dopant (namely, Ba²⁺, Sr²⁺, and Ca²⁺), are studied. The local crystal structure, chemistry, and dopant distribution are probed by analytical spherical‐aberration‐corrected scanning transmission electron microscopy. Here, the interrelation between the cationic size mismatch between dopant (M²⁺) and host La³⁺ ions and the local structure are reported, and the impact of the dopant distribution on the structural (CuO₆ octahedra elongation) local properties is discussed. A clear correlation between dopant size and local lattice deformations is highlighted. Moreover, a relation between the nature of superconductivity (bulk vs interface) and JT distortions of the anionic sublattice is suggested.