Interfaces in {100} epitaxial heterostructures of perovskite oxides

Abstract

The exact perovskite structure has simple cubic symmetry and composition ABO₃, where A is a relatively large cation and B a smaller one. The choices of A and B cations, and the substitutions possible on either site, generate a large variety of materials sharing the same base, with relatively small distortions of the size and shape of the cube. In addition, these oxides often allow oxygen non-stoichiometry with or without order to the amount of several percent. They form a vast set of technologically important materials due to their conducting, insulating, ferroelectric, magnetic, superconducting, etc., properties. Heteroepitaxy of perovskite oxides allows one to construct atomically sharp interfaces between these materials and therefore to envisage a set of useful heterojunctions. The epitaxy has side effects that may also prove useful: (1) it forces a chemical neighbouring that would not occur naturally, creating a two-dimensional third material, and (2) it imposes a lateral strain. Both of these effects allow one to explore novel, sometimes unforeseen, properties with a strong two-dimensional character. This paper first reviews some of the knowledge that has been accumulated on {100} surfaces and interfaces of perovskites, with an emphasis on properties that could be used in future all-oxide microelectronics. It then exposes the case of the interface between the half-metal La_2/3Sr_1/3MnO₃ and the insulator SrTiO₃, which plays a key role in the magnetoresistance of magnetic tunnel junctions. It particularly presents thorough electron energy loss spectroscopy measurements that uncover the atomic scale structural and electronic properties of these objects.

Acknowledgements

The authors wish to thank M. Bibes (Institut d’Electronique Fondamentale, Orsay, France), A. Barthélémy and A. Fert (UMP CNRS/Thales), for helpful discussions, A. Gloter (LPS Orsay) for critical reading of the manuscript, and É. Jacquet (UMP CNRS/Thales) for the PLD growth.