Structural Basis for the Conducting Interface between LaAlO_ {3} and SrTiO_ {3} (original) (raw)
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Structure-Property Relation of SrTiO3-LaAlO3 Interfaces
2008
A large variety of transport properties have been observed at the interface between the insulating oxides SrTiO 3 and LaAlO 3 such as insulation, 2D interface metallicity, 3D bulk metallicity, magnetic scattering, and superconductivity. The relation between the structure and the properties of the SrTiO 3 /LaAlO 3 interface can be explained in a meaningful way by taking into account the relative contribution of three structural aspects: oxygen vacancies, structural deformations (including cation disorder), and electronic interface reconstruction. The emerging phase diagram is much richer than for related bulk oxides due to the occurrence of interface electronic reconstruction. The observation of this interface phenomenon is a display of recent advances in thin film deposition and characterization techniques, and provides an extension to the range of exceptional electronic properties of complex oxides.
Physical Review B, 2011
Here, we demonstrate a structural interaction between LaAlO 3 thin films and SrTiO 3 substrates using highresolution x-ray diffraction. X-ray diffraction profiles reveal the presence of periodic lattice distortions in the LaAlO 3 thin films, whose in-plane periodicity is determined by the miscut angle and miscut direction of the substrate. We show that the structural distortions in LaAlO 3 thin films induce similar distortions in the SrTiO 3 substrate.
Physical Review Letters, 2009
Medium-energy ion spectroscopy (MEIS) has been used to study the depth profile and deduce the distribution of possible cationic substitutions in LaAlO 3 =SrTiO 3 (LAO/STO) heterointerfaces. Analysis of La and Sr peaks in aligned and random MEIS spectra indicates that the surface layers of LAO on an STO substrate are not homogeneous and stoichiometric if the film thickness is less than 4 unit cell layers. This is possibly caused by a redistribution of La and Sr at the interface. Kelvin probe force microscopy reveals an inhomogeneous distribution of the surface potential in a 4 unit cell LAO film, indicating micrometersized regions of different compositions. Our findings provide a novel view on the microstructural origin of the electrically conductive interfaces.
Structural Comparison of n-Type and p-Type LaAlO_{3}/SrTiO_{3} Interfaces
Physical Review Letters, 2011
Using a surface x-ray diffraction technique, we investigated the atomic structure of two types of interfaces between LaAlO 3 and SrTiO 3 , that is, p-type (SrO/AlO 2) and n-type (TiO 2 /LaO) interfaces. Our results demonstrate that the SrTiO 3 in the sample with the n-type interface has a large polarized region, while that with the p-type interface has a limited polarized region. In addition, the atomic intermixing was observed to extend deeper into STO substrate at the n-type interface than at the p-type. These differences result in different degrees of band bending, which likely contributes to the striking difference in electrical conductivity between the two types of interfaces.
Electronic and Magnetic Properties of SrTiO3/LaAlO3 Interfaces from First Principles
Advanced Materials, 2010
A number of intriguing properties emerge upon the formation of the epitaxial interface between the insulating oxides LaAlO 3 and SrTiO 3 . These properties, which include a quasi two-dimensional conducting electron gas, low temperature superconductivity, and magnetism, are not present in the bulk materials, generating a great deal of interest in the fundamental physics of their origins. While it is generally accepted that the novel behavior arises as a result of a combination of electronic and atomic reconstructions and growth-induced defects, the complex interplay between these effects remains unclear. In this report, we review the progress that has been made towards unraveling the complete picture of the SrTiO 3 /LaAlO 3 interface, focusing primarily on present ab initio theoretical work and its relation to the experimental data. In the process, we highlight some key unresolved issues and discuss how they might be addressed by future experimental and theoretical studies.
Electronic properties of LaAlO3/SrTiO3n-type interfaces: a GGA+Ustudy
Journal of Physics: Condensed Matter, 2017
The rôle of electronic correlation effects for a realistic description of the electronic properties of LaAlO 3 /SrTiO 3 heterostructures as covered by the onsite Coulomb repulsion within the GGA+U approach is investigated. Performing a systematic variation of the values of the Coulomb parameters applied to the Ti 3d and La 4f orbitals we put previous suggestions to include a large value for the La 4f states into perspective. Furthermore, our calculations provide deeper insight into the band gap landscape in the space spanned by these Coulomb parameters and the resulting complex interference effects. In addition, we identify important correlations between the local Coulomb interaction within the La 4f shell, the band gap, and the atomic displacements at the interface. In particular, these on-site Coulomb interactions influence buckling within the LaO interface layer, which via its strong coupling to the electrostatic potential in the LAO overlayer causes considerable shifts of the electronic states at the surface and eventually controls the band gap.
Epl, 2014
Here we investigate LaAlO3-SrTiO3 heterostructure with δ-doping of the interface by LaMnO3 at less than one monolayer. This doping strongly inhibits the formation of mobile electron layer at the interface. This results in giant increase of the resistance and the thermopower of the heterostructure. Several aspects of this phenomena are investigated. A model to calculate the carrier concentration is presented and effect of doping and detailed temperature dependence is analyzed in terms of model parameters and the weak-scattering theory. The large enhancement of thermopower is attributed to the increased spin and orbital entropy originating from the LaMnO3 mono-layer.
Polarization-controlled synchrotron radiation was used to map the electronic structure of buried conducting interfaces of LaAlO 3 /SrTiO 3 in a resonant angle-resolved photoemission experiment. A strong polarization dependence of the Fermi surface and band dispersions is demonstrated, highlighting different Ti 3d orbitals involved in two-dimensional (2D) conduction. Measurements on samples with different doping levels reveal different band occupancies and Fermi-surface areas. The photoemission results are directly compared with advanced first-principles calculations, carried out for different 3d-band filling levels connected with the 2D mobile carrier concentrations obtained from transport measurements, with indication of charge localization at the interface.
Electronic structure of the SrTiO3/LaAlO3 interface revealed by resonant soft x-ray scattering
2011
We investigated the electronic structure of the SrTiO3/LaAlO3 superlattice (SL) by resonant soft x-ray scattering. The (003) peak, which is forbidden for our "ideal" SL structure, was observed at all photon energies, indicating reconstruction at the interface. From the peak position analyses taking into account the effects of refraction, we obtained evidence for electronic reconstruction of Ti 3d and O 2p states at the interface. From reflectivity analyses, we concluded that the AlO2/LaO/TiO2/SrO and the TiO2/SrO/AlO2/LaO interfaces are quite different, leading to highly asymmetric properties.