Interface exchange processes in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">LaAlO</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>/</mml:mo><mml:mi mathvariant="normal">Sr</mml:mi><mml:msub><mml:mi mathvariant="normal">TiO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>induced by oxygen vacancies

Behrmann, Malte; Lechermann, Frank

doi:10.1103/physrevb.92.125148

Cited by 21 publications

(30 citation statements)

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“…The correlation-induced confining, here generated via the double-vacancy defect, will then be realized more effectively [19,20]. For larger numbers of OVs the e g -t 2g hybridization and -exchange will be such that e g -like states participate in the low-energy transport [19,40]. Further study of that crossover and inclusion of other possibly relevant ingredients such as the interplay of correlations and spin-orbit coupling beyond DFT+U or of improved non-local exchange-correlation treatments [41] are tasks for future theoretical work.…”

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Electron dichotomy on theSrTiO3defect surface augmented by many-body effects

et al. 2016

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In a common paradigm, the electronic structure of condensed matter is divided into weakly and strongly correlated compounds. While conventional band theory usually works well for the former class, many-body effects are essential for the latter. Materials like the familiar SrTiO3 compound that bridge or even abandon this characterization scheme are highly interesting. Here it is shown by means of combining density functional theory with dynamical-mean field theory that oxygen vacancies on the STO (001) surface give rise to a dichotomy of weakly-correlated t2g low-energy quasiparticles and localized 'in-gap' states of dominant eg character with subtle correlation signature. We furthermore touch base with recent experimental work and study the surface instability towards magnetic order.The SrTiO 3 (STO) compound has long been known for its paraelectric [1], semiconducting [2] and superconducting properties [3]. Renewed interest is fostered by the findings of a conducting two-dimensional electron system (2DES) on the STO surface [4,5], of intricate magnetic response [6], as well as due to its intriguing role as a prominent building block in novel oxide heterostructures ([7, 8], see e.g. [9, 10] reviews). In this respect, several experiments [4,5,[11][12][13] point towards the importance of oxygen vacancies for the plethora of physics emerging from the inconspicuous bulk band insulator.Stoichiometric strontium titanate is rather unsusceptible to electronic correlations due to nominal Ti 4+ (3d 0 ) valence. However, doping transforms STO into a material with potential for salient signatures of correlation effects. Usually the competition between electron localization and itinerancy in materials can be traced back to the interacting many-body system at stoichiometry. In doped STO, in contrast, defects have to build up the general correlated electronic structure from localized states affecting the low-energy quasiparticle (QP) nature beyond a conventional Anderson-model perspective.The orbital character, filling, correlation strength and mobility of the key electronic states in doped STO is of main interest. In principle, electron doping as introduced by oxygen vacancies could fill the empty Ti-3d(t 2g ) states at low energy. However creating an oxygen vacancy (OV) breaks the bond between Ti-3d(e g ) and O-2p. It has been shown [14][15][16][17][18][19][20][21] that as a result also 3d(e g ) spectral weight appears just below the Fermi level ε F of the established metallic state. Investigations based on density functional theory (DFT) identify this e g weight as associated with an 'in-gap' level due to the vacancy-induced crystal-field lowering. Depending on the local structural deformation, Ti charging, vacancy concentration and energy distance to ε F , that spectral feature may also be interpreted as a small polaron. The latter is here defined by the localization of one electron at an isolated Ti site, i.e. forming Ti 3+ , with sizable distortion of the surrounding oxygen octahedron and binding energy ∼ −1eV [22]. Rec...

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Electron dichotomy on theSrTiO3defect surface augmented by many-body effects

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“…Instead, a model-Hamiltonian approach, equipped with the relevant ingredients from the dense-defect limit, appears more adequate. Figure 8 displays the setting and some main results of such an ansatz (Behrmann and Lechermann 2015). A two-orbitalẽ g -xy Hubbard model is solved on a 10×10 square lattice resembling the TiO 2 interface plane.…”

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Oxide Heterostructures from a Realistic Many-Body Perspective

Lechermann¹

2018

Handbook of Materials Modeling

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Oxide heterostructures are a new class of materials by design, that open the possibility for engineering challenging electronic properties, in particular correlation effects beyond an effective single-particle description. This short review tries to highlight some of the demanding aspects and questions, motivated by the goal to describe the encountered physics from first principles. The state-of-the-art methodology to approach realistic many-body effects in strongly correlated oxides, the combination of density functional theory with dynamical mean-field theory, will be briefly introduced. Discussed examples deal with prominent Mott-band-and bandband-insulating type of oxide heterostructures, where different electronic characteristics may be stabilized within a single architectured oxide material.

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“…We derived a minimal two-orbital model, consisting of a t 2g (xy) state and an effective e g state, i.e.,ẽ g [96]. The latter is lowered by crystal-field effects if an OV is adjacent.…”

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“…The first-principles point of view renders it possible to utilize effective (e g ,t 2g ) modellings [53,96]. We derived a minimal two-orbital model, consisting of a t 2g (xy) state and an effective e g state, i.e.,ẽ g [96].…”

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“…Since an oxygen vacancy (OV) in SrTiO 3 singularly modifies the electronic structure on the local level, i.e., from Ti(d 0 ) towards Ti(d 1 ), we follow here a twofold supercell strategy to assess the dense and dilute defect cases. Realistic superlattice DMFT calculations are performed for the dense defect limit [95] and a derived model Hamiltonian is applied to a large real-space lattice to treat the crossover to dilute defect scenarios [96]. Figure 11a shows the used inplane-doubled dense defect n-type supercell, with OVs in the TiO 2 layer right at the interface, whereby one out of four oxygen sites is vacant.…”

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Influence of oxygen vacancies on two-dimensional electron systems at SrTiO3-based interfaces and surfaces

Sing

Jeschke

Lechermann

et al. 2017

Eur. Phys. J. Spec. Top.

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Abstract. The insulator SrTiO 3 can host high-mobility twodimensional electron systems on its surfaces and at interfaces with other oxides. While for the bare surface a two-dimensional electron system can only be induced by oxygen vacancies, it is believed that the metallicity of heterostructure interfaces as in LaAlO 3/SrTiO3 is caused by other mechanisms related to the polar discontinuity at the interface. Based on calculations using density functional and dynamical mean-field theory as well as on experimental results using photoemission spectroscopy we elucidate the role of oxygen vacancies, thereby highlighting their importance for the electronic and magnetic properties of the systems under study.

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Interface exchange processes inLaAlO3/SrTiO3induced by oxygen vacancies

Cited by 21 publications

References 61 publications

Electron dichotomy on theSrTiO3defect surface augmented by many-body effects

Electron dichotomy on theSrTiO3defect surface augmented by many-body effects

Oxide Heterostructures from a Realistic Many-Body Perspective

Influence of oxygen vacancies on two-dimensional electron systems at SrTiO3-based interfaces and surfaces

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