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Currently, the formation of a two-dimensional electron gas (2DEG) at the TiO2/LaO-terminated interface between LaAlO3 (LAO) grown on SrTiO3(001) (STO) is well understood. The role of the polarity of LAO and its critical thickness for the formation of 2DEG have been established. Here, we show how 2DEG can be tuned externally by changing electronic balance at the LAO(001) surface or, alternatively, at the intrinsically hole-doped AlO2/SrO interface of LAO/STO heterostructures. The effects of liquid gating at LAO(001) and imperfected AlO2/SrO were simulated in the framework of the first-principles Green function method within the coherent-potential approximation. We evaluated the Fermi surface cross sections, which were computed varying the degree of chemical disorder. These findings may be extremely important for potential application of 2DEG.

Interfaces of ferroic oxides can show complex magnetic textures which have strong impact on spintronics devices. This has been demonstrated recently for interfaces with insulating antiferromagnets such as BiFeO3. Here, noncollinear spin textures which can be switched in very low magnetic field are reported for conducting ferromagnetic bilayers of La0.7Sr0.3MnO3-SrRuO3 (LSMO-SRO). The magnetic order and switching are fundamentally different for bilayers coherently grown in reversed stacking sequence. The SRO top layer forms a persistent exchange spring which is antiferromagnetically coupled to LSMO and drives switching in low fields of a few milliteslas. Density functional theory reveals the crucial impact of the interface termination on the strength of Mn-Ru exchange coupling across the interface. The observation of an exchange spring agrees with ultrastrong coupling for the MnO2/SrO termination. Our results demonstrate low-field switching of noncollinear spin textures at an interface between conducting oxides, opening a pathway for manipulating and utilizing electron transport phenomena in controlled spin textures at oxide interfaces.

Double perovskites (DPs) are a large family of compounds that exhibit a wide range of properties of both fundamental and potential technological interest. Due to the presence of 3d,4d, or 5d transition metal atoms with narrow t2g and eg bands in DPs, the correlation effects play an important role for the properties of these materials, leading to diverse physical phenomena, such as colossal magnetoresistance, ferroelectricity, magnetism, and superconductivity. By employing the constrained random-phase approximation within the full-potential linearized augmented-plane-wave method, we have calculated the effective on-site Coulomb interaction parameters between localized d electrons in Sr2ABO6(A=Cr,Mn,Fe,Co,Ni, and B=Mo,W) DPs. We find that the correlated subspace can be defined to contain only the eg states in Ni-based compounds, leading to a simple two-band low-energy model, whereas at least an eight-orbital (d+t2g) model is necessary for the other compounds. Except for Ni, the U values for A sites in Mo (W) based compounds are around 4 eV (4.5 eV), and they are almost independent of the 3d electron number, while the U for Mo (W) t2g electrons slightly decreases with increasing 3d electron number, from 3 to 2.5 eV. Moreover, our calculations reveal that the contribution of the 3d→3d channel to the total electronic screening is larger in DPs than the corresponding contribution in elementary transition metals

Spin caloric transport refers to the coupling of heat with spin transport. Its applications primarily concern the generation of spin currents and control of magnetisation by temperature gradients for information technology, known by the synonym spin caloritronics. Within the framework of ab initio theory, new tools are being developed to provide an additional understanding of these phenomena in realistic materials, accounting for the complexity of the electronic structure without adjustable parameters. Here, we review this progress, summarising the principles of the density-functional-based approaches in the field and presenting a number of application highlights. Our discussion includes the three most frequently employed approaches to the problem, namely the Kubo, Boltzmann, and Landauer-Büttiker methods. These are showcased in specific examples that span, on the one hand, a wide range of materials, such as bulk metallic alloys, nano-structured metallic and tunnel junctions, or magnetic overlayers on heavy metals, and, on the other hand, a wide range of effects, such as the spin-Seebeck, magneto-Seebeck, and spin-Nernst effects, spin disorder, and the thermal spin-transfer and thermal spin-orbit torques. © 2018 IOP Publishing Ltd.

A two-dimensional electron gas (2DEG) can be formed at an interface between two insulators such as LaAlO3 and SrTiO3 without any additional doping. Nevertheless, structural imperfections or defects at the interface, which may arise during the growth process or be of another origin, can definitely affect 2DEG properties either increasing or reducing the 2DEG density. In this work, we study 2DEG formation at both perfect and imperfect interfaces of LaAlO3/SrTiO3 heterostructures in the framework of the density functional theory. Using a first-principles Green function method within a coherent potential approximation, we investigate consistently the development of the 2DEG density starting from a defectless interface and introducing sequentially various kinds of long-range disorder such as cation intermixing and oxygen vacancies. Finally, we evaluate the 2DEG carrier density from the Fermi surface cross sections and effective masses of the carriers, which may be directly related to the multiple transport phenomena in the system.

A surge in interest of oxide‐based materials is testimony for their potential utility in a wide array of device applications and offers a fascinating landscape for tuning the functional properties through a variety of physical and chemical parameters. In particular, selective electronic/defect doping has been demonstrated to be vital in tailoring novel functionalities, not existing in the bulk host oxides. Here, an extraordinary interstitial doping effect is demonstrated centered around a light element, boron (B). The host matrix is a novel composite system, made from discrete bulk LaAlO3:LaBO3 compounds. The findings show a spontaneous ordering of the interstitial B cations within the host LaAlO3 lattices, and subsequent spin‐polarized charge injection into the neighboring cations. This leads to a series of remarkable cation‐dominated electrical switching and high‐temperature ferromagnetism. Hence, the induced interstitial doping serves to transform a nonmagnetic insulating bulk oxide into a ferromagnetic ionic-electronic conductor. This unique interstitial B doping effect upon its control is proposed to be as a general route for extracting/modifying multifunctional properties in bulk oxides utilized in energy and spin‐based applications.

The scope of this work is to review the thermoelectric properties, the microstructures, and their correlation with theoretical calculations and predictions for recent chalcogenide based materials. The main focus is put on thin multilayered Bi2Te3, Sb2Te3 films, and bulk V2VI3/IV-VI mixed systems. For all films a systematic characterization of the thermoelectric properties as well as the micro- and nanostructure was performed. The degree of crystallinity of the multilayered films varied from epitaxial systems to polycrystalline films. Other multilayered thin films revealed promising thermoelectric properties. (SnSe)1.2TiSe2 thin films with rotational disorder yielded the highest Seebeck coefficient published to date for analogous materials. For bulk V2VI3/IV-VI mixed systems insides are given into a complete ""material to module"" process resulting in a high performance thermoelectric generator using (1-x)(GeTe) x(Bi2Se0.2Te2.8) (x = 0.038). Cyclic heating of this system with x = 0.063 resulted in a drastic change of the micro- and nanostructure observed by ex situ and in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM). Consequently a degradation of ZT at 450 °C from ∼2.0 to ∼1.0 was observed, while samples with x = 0.038 showed a stable ZT of 1.5.

The scope of this review is to present the recent progress in the understanding of the microscopic origin of thermoelectric transport in semiconducting heterostructures and to identify and elucidate mechanisms which could lead to enhanced thermoelectric conversion efficiency. Based on first-principles calculations a consistent and convenient method is presented to fully describe the thermoelectric properties in the diffusive limit of transport for bulk systems and their associated heterostructures. While fundamentals of the functionality of phonon-blocking and electron-transmitting superlattices could be unveiled, we provide also distinct analysis and ideas for thermoelectric enhancement for two archetypical thermoelectric heterostructures based on inline image and Si/Ge. A focus was on the influence of bulk and interfacial strain, varying charge carrier concentration, temperature, and superlattice periods on the thermoelectric transport properties.

Resumen del trabajo presentado al New Trends in Topological Insulators (NTTI), celebrado en Donostia-San Sebastián (España) del 6 al10 de julio de 2015., FM thanks ‘Financiamiento Basal para Centros Cientificos y Tecnologicos de Excelencia FB 0807’ and Fondecyt grants 11110510, 1150806.

Thermoelectric properties are calculated within a quasi-classical transport theory based on the Boltzmann equation. We consider Bi2Te3 as bulk material and in multilayered structures. Directional anisotropies of the transport coefficients and changes caused by the layered structure with respect to the bulk materials are discussed in detail.