Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 22: Low-dimensional Systems - Materials

TT 22.6: Talk

Thursday, March 29, 2007, 10:45–11:00, H18

Correlation driven charge order at LaAlO₃/SrTiO₃ and LaTiO₃/SrTiO₃ Interfaces — •Rossitza Pentcheva¹ and Warren Pickett² — ¹Section Crystallography, Dept. of Earth and Environmental — ²Department of Physics, University of California, Davis,

To explain recent experiments reporting metallic conductivity at the interfaces between the Mott insulator LaTiO₃ (LTO) and band insulator SrTiO₃ (STO) but also between the two simple band insulators LaAlO₃ (LAO) and STO we have performed density-functional theory calculations employing the FP-LAPW-method within the WIEN2k implementation including a Hubbard-type on site Coulomb repulsion (DFT+U). We find that charge mismatch at the LTO/STO IF is accommodated by the formation of a charge and orbitally ordered (CO/OO) layer with a checkerboard arrangement of Ti³⁺ and Ti⁴⁺ and an antiferromagnetic coupling of the Ti³⁺-spins [1]. Lattice relaxations lead to the observed conducting behavior. An analogous diluted layer of Ti³⁺ spins is obtained for the n-type LAO/STO interface, although the corresponding bulk materials are nonmagnetic [2]. For a structurally ideal p-type LAO/STO IF strong correlations in the oxygen p states and the formation of a charge and orbitally ordered O Pπ magnetic hole render a possible explanation for the measured insulating behavior. Alternatively, charge compensation by oxygen vacancies and the formation of a charge conjugate F-center is considered.

[1] R. Pentcheva and W.E. Pickett, cond-mat/0608212.

[2] R. Pentcheva and W.E. Pickett, Phys. Rev. B. 74, 035112 (2006).