Driving Forces and Challenges of Interfacing Functional Oxide Perovskites

Perovskite (ABO₃) oxides are by no exaggeration an extremely versatile class of materials, exhibiting a broad spectrum of fascinating physical properties: superconductivity, ferromagnetism, ferroelectricity, multiferroic behavior. Scaling down from bulk single crystals to thin and ultrathin (few unit cell thick) epitaxial films the first question is to what extent we are capable to preserve the properties of the bulk and understand the role played by epitaxial growth in changing the physical properties. Another degree of freedom and of complexity as well arises when we interface coherently thin films of two or more chemically and physically different oxides. On one hand, the interfacing poses challenges in terms of finding the fabrication conditions that satisfy the needs of all partners. On the other hand, new physical properties may arise at the interfaces: these are the driving forces for heterostructures and superlattices of perovskite oxides, with a boom of efforts in the last decades, supported by the progress in molecular beam epitaxy and pulsed-laser deposition of complex oxides. Simultaneously the advances of high resolution and scanning transmission electron microscopy with analytical accessoires (EELS, EDX) have been of tremendous help in investigating such heterostructures with unprecedented spatial resolution, contributing directly to the understanding of the physical properties at a unit cell level. In order to underline these statements, I shall give example of the physical properties of heterostructures and superlattices of ferromagnetic and ferroelectric perovskites from my work.