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

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 JahnTeller (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 La1.6M0.4CuO4, 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.