The generic perovskite unit cell is a simple cube of formula ABO₃ where A and B are respectively a large and a small cation. Depending on the nature of cations, the substitutions on either cationic site, and the amount and possible order of oxygen vacancies, perovskite oxides span an extremely wide range of solid state electronic and magnetic properties. Associating them by epitaxy creates a large field of research towards applications in the microelectronics area, in a context where silicon-based technology faces major challenges.

In <100> directions, perovskites are stacks of {200} planes of alternate compositions AO and BO₂; there are thus two possibilities of stacking sequence at a {100} interface. Depending on the valency of the different cations in presence, these two may have dramatically different properties: at the interface between the insulators LaAlO₃ and SrTiO₃ for instance, high-mobility carriers were detected in the case of the -LaO-TiO₂- sequence while the sequence -AlO₂-SrO- was found insulating [1].

In order to reproduce the metallic -LaO-TiO₂- interface, we have grown LaAlO₃ onto TiO₂-terminated (001) SrTiO₃ using pulsed laser deposition; the samples obtained were conducting indeed. We have then observed this interface at the atomic level by aberration-corrected high-resolution transmission electron microscopy and electron energy loss spectroscopy. On the basis of our experimental observations, we discuss in this communication the origin of the measured electronic properties.

[1] A. Ohtomo and H. Y. Hwang, Nature 427, 423 (2004)

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