Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 33: Postersession Correlated Electrons: Metal Insulator Transition, Spin Systems and Itinerant Magnets

TT 33.6: Poster

Mittwoch, 25. März 2009, 14:00–18:00, P1A

Lattice distortions in oxide heterostructures — •Cosima Schuster¹ and Udo Schwingenschlögl² — ¹Institut für Physik, Universität Augsburg, D-86135 Augsburg — ²ICCMP, Universidade de Brasilia, 70904-970 Brasilia-DF, Brazil

Perovskite heterostructures from transition metal oxides have attracted recent interest due to the discovery of metallic interlayers in an otherwise semiconducting system. For example, a metallic contact between two common band insulators is realized in the LaAlO₃/SrTiO₃ heterointerface. Nevertheless, it was shown experimentally that the LaAlO₃ surface layer must reach a critical thickness of 4 unit cells for the interface to become conducting. This surface effect can be explained by first-principles electronic structure calculations. On varying the thickness of the LaAlO₃-layer on a SrTiO₃-substrate with a vacuum layer of at least 12 Å thickness, we have found that the interface conduction states are subject to almost rigid band shifts due to a modified Fermi energy. In addition, we take into account structural relaxation at both the LaAlO₃/SrTiO₃ interface and the LaAlO₂ surface. Drastic alterations are obtained on variation of the layer thicknesses. The distortion of the TiO₆ octahedra in the four layer structure is comparable to the multi-layer system (without surface) and enhances the metallicity in the vicinity of the interface. Modified and enhanced lattice distortions in the two layer system support an insulating state. Cooperative effects induced by the interplay between the interface/surface lattice relaxation and the electrostatic charge depletion explain the matal insulator transition.