Academic literature on the topic 'Exotic Transition Metal Oxides'

Transition metal oxides with ABO3 or BO2 structures have become one of the major research fields in solid state science, as they exhibit an impressive variety of unusual and exotic phenomena with potential for their exploitation in real-world applications [...]

Understanding the role of electron correlations in strong spin-orbit transition-metal oxides is key to the realization of numerous exotic phases including spin-orbit–assisted Mott insulators, correlated topological solids, and prospective new high-temperature superconductors. To date, most attention has been focused on the 5diridium-based oxides. We instead consider the Pt-based delafossite oxide PtCoO2. Our transport measurements, performed on single-crystal samples etched to well-defined geometries using focused ion beam techniques, yield a room temperature resistivity of only 2.1 microhm·cm (μΩ-cm), establishing PtCoO2as the most conductive oxide known. From angle-resolved photoemission and density functional theory, we show that the underlying Fermi surface is a single cylinder of nearly hexagonal cross-section, with very weak dispersion alongkz. Despite being predominantly composed ofd-orbital character, the conduction band is remarkably steep, with an average effective mass of only 1.14me. Moreover, the sharp spectral features observed in photoemission remain well defined with little additional broadening for more than 500 meV belowEF, pointing to suppressed electron-electron scattering. Together, our findings establish PtCoO2as a model nearly-free–electron system in a 5ddelafossite transition-metal oxide.

Functional oxides with strongly correlated electron systems, such as vanadium dioxide, manganite, and so on, show a metal-insulator transition and an insulator-metal transition (MIT and IMT) with a change in conductivity of several orders of magnitude. Since the discovery of phase separation during transition processes, many researchers have been trying to capture a nanoscale electronic domain and investigate its exotic properties. To understand the exotic properties of the nanoscale electronic domain, we studied the MIT and IMT properties for the VO2 electronic domains confined into a 20 nm length scale. The confined domains in VO2 exhibited an intrinsic first-order MIT and IMT with an unusually steep single-step change in the temperature dependent resistivity (R-T) curve. The investigation of the temperature-sweep-rate dependent MIT and IMT properties revealed the statistical transition behavior among the domains. These results are the first demonstration approaching the transition dynamics: the competition between the phase-transition kinetics and experimental temperature-sweep-rate in a nano scale. We proposed a statistical transition model to describe the correlation between the domain behavior and the observable R-T curve, which connect the progression of the MIT and IMT from the macroscopic to microscopic viewpoints.

Many transition-metal oxides in elevated valence states [e.g. Mn(V), Co(IV), Ni(III), Cu(III) ] present a metastable character and, given the difficulty of their synthesis, have been relatively little studied. However, they are very interesting materials presenting strong electronic correlations that are bound to exotic properties such as superconductivity, metal behavior, metal–insulator transitions or colossal magnetoresistance. The metastability of these compounds requires special synthesis conditions such as the application of high pressure. In the last years, we have prepared and investigated a good number of materials belonging to several families such as RNiO3 (R = rare earths), Ba3Mn2O8 , (Ba,Sr)CoO3 , La2(Ni,Co)O4+δ , etc. In the study and correct characterization of these oxides it has been decisive the use of elastic neutron diffraction, most of the times in powder samples. This technique has allowed us to access the structural details typically related to the octahedral tilting in perovskite structures, the oxygen stoichiometry and order–disorder of the oxygen sublattice, the distinction between close elements in the Periodic Table, the resolution of magnetic structures and, in general, the establishment of a correlation between the structure and the properties of interest. This letter is organized around the binomial "high-pressure synthesis" and "characterization by neutron diffraction" and illustrated with some selected examples among the metastable materials above mentioned.

Abstract Transition metal oxides hold a wide spectrum of fascinating properties endowed by the strong electron correlations. In 4d and 5d oxides, exotic phases can be realized with the involvement of strong spin–orbit coupling (SOC), such as unconventional magnetism and topological superconductivity. Recently, topological Hall effects (THEs) and magnetic skyrmions have been uncovered in SrRuO3 thin films and heterostructures, where the presence of SOC and inversion symmetry breaking at the interface are believed to play a key role. Realization of magnetic skyrmions in oxides not only offers a platform to study topological physics with correlated electrons, but also opens up new possibilities for magnetic oxides using in the low-power spintronic devices. In this review, we discuss recent observations of THE and skyrmions in the SRO film interfaced with various materials, with a focus on the electric tuning of THE. We conclude with a discussion on the directions of future research in this field.

Strain engineering has been demonstrated to be an effective knob to tune the bandgap in perovskite oxides, which is highly desired for applications in optics, optoelectronics, and ferroelectric photovoltaics. Multiferroic BiFeO3 exhibits great potential in photovoltaic applications and its bandgap engineering is of great interest. However, the mechanism of strain induced bandgap engineering in BiFeO3 remains elusive to date. Here, we perform in situ ellipsometry measurements to investigate the bandgap evolution as a function of uniaxial strain on freestanding BiFeO3 films. Exotic anisotropic bandgap engineering has been observed, where the bandgap increases (decreases) by applying uniaxial tensile strain along the pseudocubic [100]p ([110]p) direction. First-principles calculations indicate that different O6 octahedral rotations under strain are responsible for this phenomenon. Our work demonstrates that the extreme freedom in tuning the strain and symmetry of freestanding films opens a new fertile playground for novel strain-driven phases in transition metal oxides.

High electron affinity transition-metal oxides (TMOs) have gained a central role in two-dimensional (2D) electronics by enabling unprecedented surface charge doping efficiency in numerous exotic 2D solid-state semiconductors. Among them, diamond-based 2D electronics are entering a new era by using TMOs as surface acceptors instead of previous molecular-like unstable acceptors. Similarly, surface-doped diamond with TMOs has recently yielded record sheet hole concentrations (2 × 1014 cm−2) and launched the quest for its implementation in microelectronic devices. Regrettably, field-effect transistor operation based on this surface doping has been so far disappointing due to fundamental material obstacles such as (i) carrier scattering induced by nonhomogeneous morphology of TMO surface acceptor layer, (ii) stoichiometry changes caused by typical transistor fabrication process, and (iii) carrier transport loss due to electronic band energy misalignment. This work proposes and demonstrates a general strategy that synergistically surmounts these three barriers by developing an atomic layer deposition of a hydrogenated MoO3 layer as a novel efficient surface charge acceptor for transistors. It shows high surface uniformity, enhanced immunity to harsh fabrication conditions, and benefits from tunable electronic gap states for improving carrier transfer at interfaces. These breakthroughs permit crucial integration of TMO surface doping into transistor fabrication flows and allow outperforming electronic devices to be reached.

Carrier doping into two dimensional (2D) Mott insulators is one of the prospective strategies for exploring exotic quantum phenomena. Although ultra-thin oxide films are one such target, it is vitally important to fabricate well-defined and clean samples to extract intrinsic properties. In this study, we start from establishing the growth of clean SrVO3 films with a low residual resistivity (∼4 × 10−7 Ω cm) and a high mobility (∼103 cm2/V s). By confining them with SrTiO3 barrier layers, the Mott insulator state appears at the thickness below 3 unit cells (u.c.). By the electron doping in the form of La xSr1− xVO3 for such two dimensional systems (2 and 3 u.c), metallic-like phases appear in a narrow x region around x = 0.17, indicating a collapse of the Mott insulator state. This study demonstrates that artificial 2D systems of clean oxides are a promising playground for exploring novel Mott physics in confined systems.

With the slowing down of Moore’s law, related to conventional scaling of integrated circuits, alternative technologies will require research effort for pushing the limits of new generations of electronic or photonic devices. Perovskite oxides with the ABO3 chemical formula have a very wide range of interesting intrinsic properties such as metal-insulator transition, ferroelectricity, pyroelectricity, piezoelectricity, ferromagnetic and superconductivity. For the integration of such oxides, it is of great interest to combine their properties with traditional electronic, memory and optical devices on the same silicon-based platform. In the context of high-speed chip-to-chip optical interconnects, compact high-resolution beam steering and video-rate RGB hologram generation require the integration of fast and efficient optical modulators on top of silicon CMOS devices. For these applications the integration of high quality electro-optical materials A defect-free material-stack deposition on silicon wafers is hence required. Among the possible materials options, barium titanate (BaTiO3) is one promising candidate due to its large intrinsic Pockels coefficients that can be obtained. In a first part of the talk, we will review the different options to integrate BaTiO3 on Silicon substrate though different templates to control the polarization direction and discuss the influence on the physical, electrical and optical properties. Then in the second section we will discuss the use of perovskites oxide in the field of topological based qubits which is one of the promising methods for realizing fault-tolerant computations. It is recognized that superconductor/topological insulator heterostructure interfaces may be a perfect host for the exotic “Majorana” particles. These have relevant topological protection nature as required for processing information. Therefore, the physics at the superconductor/topological insulator heterostructure interface need to be studied further, starting at the material level. In this work, a candidate material Barium Bismuthate (BBO) is studied utilizing the Oxide Molecular Beam Epitaxy (MBE) process. The perovskite structure provides opportunity for easily tailored functionality through substitutional doping. Incorporation of potassium into the lattice of BBO results in a superconducting phase with Curie temperature as high as ~ 30K. In addition, BBO is according to DFT based studies, predicted to form topological surface states when doped with Fluorine. In our work, we integrate BBO perovskite on Si(001) substrate, using an epitaxially grown strontium titanate (STO) single-crystalline buffer layer and discuss the structural and chemical properties of the heterostructure will be established by utilizing physical characterization techniques such as AFM, and TEM in later stages. This will go hand in hand with the understanding of the ARPES studies and related surface reconstruction of BBO observed by RHEED as a criterion for the high-quality films. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreements No 864483 and 742299)”.