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Oxygen octahedron reconstruction at SrTiO3/LaAlO3 heterointerfaces investigated by aberration-corrected ultrahigh resolution TEM

IFF-News February 1, 2009

by Chunlin Jia, Shaobo Mi, Michael Faley, Ulrich Poppe, Jürgen Schubert, and Knut Urban

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Perovskite-structured oxides are known for their exceptional variety of physical properties. The observation of a highly mobile electron gas at the heterointerface between the two nominally insulating perovskites LaAlO3 and SrTiO3 has stimulated intensive research efforts concerning the physical origin of this intriguing effect and the possibility to derive from it new electronic device applications. This has added to the list of particular properties of this interface the observation of ferromagnetism below 1 Kelvin and of superconductivity below 0.2 Kelvin. The effervescent magic source of a seemingly inexhaustible flux of new and surprising properties is provided by a manifold of ways. The cationoxygen octahedra representing the prominent structural element of perovskites can be modified by, e.g., distortions, rotations, or particular atomic shifts. On the other hand, even small atomic rearrangements as they are expected to occur in interfaces between perovskites of different structure can change dramatically the electronic system.

High-resolution structural investigations are therefore highly desirable to elucidate the mechanisms behind the observed interface-related properties. Not only that the physical models have to be validated with respect to their structural consequences, all the theoretical approaches by first-principles electronic structure calculations have to start with a suitable structure model which, as long as atomic details are not available, is largely constructed based on the perfect or further simplified bulk structures. In the light of the versatility of physical properties of perovskites and the complex response to even very small atomic rearrangements, progress in the atomic characterization will help to advance the theoretical modeling of the
interfaces.

In the present work we investigate the atomic structure of LaO-TiO2-type interfaces in epitactic LAO/STO heterostructures by means of aberration-corrected ultrahigh-resolution transmission electron microscopy. Employing the negativespherical aberration imaging technique we reveal substantial rearrangements of the oxygen octahedra in the interface as well as in the adjacent areas. We find that the oxygen octahedron rotation typical for rhombohedral LaAlO3 is across the interface and is also induced in the originally cubic SrTiO3 layer. Octahedra distortion leads to ferroelectricitylike dipole formation in the interface which is in addition modified by cation intermixing.

Further reading:

Chunlin Jia, Shaobo Mi, Michael Faley, Ulrich Poppe, Jürgen Schubert, and Knut Urban: Oxygen octahedron reconstruction in the SrTiO3/LaAlO3 heterointerfaces investigated using aberration-corrected ultrahigh-resolution transmission electron microscopy, Phys. Rev. B 79 (2009) 081405.


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