Magnetotransport properties of metal/LaAlO3/SrTiO3 heterostructures

The quasi two-dimensional electron gas (q2DEG) hosted in the interface of an epitaxially grown lanthanum aluminate (LaAlO3) thin film with a TiO2-termi-nated strontium titanate (SrTiO3) substrate (001) has been massively studied in the last few years. The confinement of mobile electrons to within a few nanome-ters from the interface, superconductive behavior at low temperatures and elec-tron mobility exceeding 1000 cm2/(V.s) make this system an interesting candi-date to explore the physics of spin injection and transport. However, due to the critical thickness for conduction of 4 unit cells (uc) of LaAlO3, a high tunneling resistance hampers electrical access to the q2DEG, preventing proper injection of spin polarized current. Recently, our group found that depositing a thin overlayer of Co on LaAlO3 reduces the critical thickness, enabling conduction with only 1 uc of LaAlO3. Two scenarios arise to explain this phenomenon: a pinning of the Fermi level in the metal, inducing charge transfer in the SrTiO3; the creation of oxygen vacancies at the interface between LaAlO3 and the metal, leading to an n-type doping of the SrTiO3. In this dissertation, we will report on magnetotransport of metal/LaAlO3/SrTiO3 (metal: Ti, Ta, Co, Py, Au, Pt, Pd) heterostructures with 2 uc of LaAlO3 studied at low temperatures (2 K) and high magnetic fields (9 T). We have analyzed the transport properties of the gas, namely, the carrier concen-tration, mobility and magnetotransport regime and we will discuss the results in the light of the two scenarios mentioned above

Oxide spin-orbitronics: New routes towards low-power electrical control of magnetization in oxide heterostructures

International audienceThe transition metal oxide family harbors various types of materials of interest for spintronics: half-metallic manganites are highly efficient spin injectors and detectors, yielding record values of tunnel magnetoresistance; multiferroic materials, and in particular BiFeO 3 , allow the electrical control of magnetization and spin excitations at room temperature; combined with ferromagnets, piezoelectric perovskites enable a controlled tuning of magnetic anisotropy, domain dynamics and even magnetic order. In this review, we argue that a new opportunity is emerging for oxides in spintronics with the rise of spin-orbit-driven phenomena such as the direct and inverse spin Hall and Rashba-Edelstein effects. After surveying the few results reported on inverse spin Hall measurements in oxide materials, we describe in depth the physics of SrTiO 3-based interfaces and their usage for both spin-to-charge and charge-to-spin conversion. Finally, we give perspectives for a more thorough exploration of spin Hall effects in oxides and enhanced conversion ratios in both three-and two-dimensional structures

Analysis of generation and characterization of construction and demolition waste on construction sites in the city of Recife, Brazil

In order to planning the Construction and Demolition Waste (CDW) management approach on a constructionsite, it is necessary to have a prior knowledge of what is being generated (qualitative analysis), the quantitythat is being generated (quantitative analysis), and what is the proper final destination assigned to thismaterial. This article proposes a new method to estimate CDW generation in Brazil from a qualitative andquantitative analysis of CDW generation in worksites. For the waste characterization, it was used thecompression test with energy of Standard Proctor Test, granulometric analysis, microstructure analysis anddirect shear tests. For the quantitative data collection, the research was limited to worksites of residential orcommercial multi-story buildings, with reinforced concrete structure, which is the most common type used inBrazil. The data on the number of waste bins removed monthly, transportation and final disposal, CDWmanagement costs, and constructive process were obtained from the construction companies.Keywords: civil construction, waste management, characterization

Streptococcus pyogenes Causing Skin and Soft Tissue Infections Are Enriched in the Recently Emerged emm89 Clade 3 and Are Not Associated With Abrogation of CovRS

Although skin and soft tissue infections (SSTI) are the most common focal infections associated with invasive disease caused by Streptococcus pyogenes (Lancefield Group A streptococci - GAS), there is scarce information on the characteristics of isolates recovered from SSTI in temperate-climate regions. In this study, 320 GAS isolated from SSTI in Portugal were characterized by multiple typing methods and tested for antimicrobial susceptibility and SpeB activity. The covRS and ropB genes of isolates with no detectable SpeB activity were sequenced. The antimicrobial susceptibility profile was similar to that of previously characterized isolates from invasive infections (iGAS), presenting a decreasing trend in macrolide resistance. However, the clonal composition of SSTI between 2005 and 2009 was significantly different from that of contemporary iGAS. Overall, iGAS were associated with emm1 and emm3, while SSTI were associated with emm89, the dominant emm type among SSTI (19%). Within emm89, SSTI were only significantly associated with isolates lacking the hasABC locus, suggesting that the recently emerged emm89 clade 3 may have an increased potential to cause SSTI. Reflecting these associations between emm type and disease presentation, there were also differences in the distribution of emm clusters, sequence types, and superantigen gene profiles between SSTI and iGAS. According to the predicted ability of each emm cluster to interact with host proteins, iGAS were associated with the ability to bind fibrinogen and albumin, whereas SSTI isolates were associated with the ability to bind C4BP, IgA, and IgG. SpeB activity was absent in 79 isolates (25%), in line with the proportion previously observed among iGAS. Null covS and ropB alleles (predicted to eliminate protein function) were detected in 10 (3%) and 12 (4%) isolates, corresponding to an underrepresentation of mutations impairing CovRS function in SSTI relative to iGAS. Overall, these results indicate that the isolates responsible for SSTI are genetically distinct from those recovered from normally sterile sites, supporting a role for mutations impairing CovRS activity specifically in invasive infection and suggesting that this role relies on a differential regulation of other virulence factors besides SpeB

Streptococcus canis Are a Single Population Infecting Multiple Animal Hosts Despite the Diversity of the Universally Present M-Like Protein SCM

Streptococcus canis is an animal pathogen which occasionally causes infections in humans. The S. canis M-like protein (SCM) encoded by the scm gene, is its best characterized virulence factor but previous studies suggested it could be absent in a substantial fraction of isolates. We studied the distribution and variability of the scm gene in 188 S. canis isolates recovered from companion animals (n = 152), wild animal species (n = 20), and humans (n = 14). Multilocus sequence typing, including the first characterization of wildlife isolates, showed that the same lineages are present in all animal hosts, raising the possibility of extensive circulation between species. Whole-genome analysis revealed that emm-like genes found previously in S. canis correspond to divergent scm genes, indicating that what was previously believed to correspond to two genes is in fact the same scm locus. We designed primers allowing for the first time the successful amplification of the scm gene in all isolates. Analysis of the scm sequences identified 12 distinct types, which could be divided into two clusters: group I (76%, n = 142) and group II (24%, n = 46) sharing little sequence similarity. The predicted group I SCM showed extensive similarity with each other outside of the N-terminal hypervariable region and a conserved IgG binding domain. This domain was absent from group II SCM variants found in isolates previously thought to lack the scm gene, which also showed greater amino acid variability. Further studies are necessary to elucidate the possible host interacting partners of the group II SCM variants and their role in virulence

Catálogo Taxonômico da Fauna do Brasil: setting the baseline knowledge on the animal diversity in Brazil

The limited temporal completeness and taxonomic accuracy of species lists, made available in a traditional manner in scientific publications, has always represented a problem. These lists are invariably limited to a few taxonomic groups and do not represent up-to-date knowledge of all species and classifications. In this context, the Brazilian megadiverse fauna is no exception, and the Catálogo Taxonômico da Fauna do Brasil (CTFB) (http://fauna.jbrj.gov.br/), made public in 2015, represents a database on biodiversity anchored on a list of valid and expertly recognized scientific names of animals in Brazil. The CTFB is updated in near real time by a team of more than 800 specialists. By January 1, 2024, the CTFB compiled 133,691 nominal species, with 125,138 that were considered valid. Most of the valid species were arthropods (82.3%, with more than 102,000 species) and chordates (7.69%, with over 11,000 species). These taxa were followed by a cluster composed of Mollusca (3,567 species), Platyhelminthes (2,292 species), Annelida (1,833 species), and Nematoda (1,447 species). All remaining groups had less than 1,000 species reported in Brazil, with Cnidaria (831 species), Porifera (628 species), Rotifera (606 species), and Bryozoa (520 species) representing those with more than 500 species. Analysis of the CTFB database can facilitate and direct efforts towards the discovery of new species in Brazil, but it is also fundamental in providing the best available list of valid nominal species to users, including those in science, health, conservation efforts, and any initiative involving animals. The importance of the CTFB is evidenced by the elevated number of citations in the scientific literature in diverse areas of biology, law, anthropology, education, forensic science, and veterinary science, among others

Conversion courant de spin en courant de charge dans les gaz d'électrons bidimensionnels à base de SrTiO3

This thesis is composed by four chapters. In the first, we start by introducing basic concepts in spintronics, such as the electron spin, a definition of spin current, and how spins behave in real materials. Then, we review the main consequences of the relation between charge and spin currents in different materials, and how a charge current can be converted in a spin current (and vice-versa). In particular scenarios, the physics of the interconversion follows special symmetry considerations in the framework of the Dressllehaus and Rashba effects, which in turn explain the spin-to-charge current interconversion in 2D electron gases through the direct and inverse Edelstein effect. In the second chapter, we introduce the main material used throughout this thesis: strontium titanate (SrTiO3). After reviewing its main features, we explore the remarkable 2D elec-tron gas found in the LaAlO3/SrTiO3 system. We discuss in detail the origin of the interfacial conductivity that arises between these two insulators, the critical thickness for conduction of 4 unit cells of LaAlO3, and the main mechanisms that lead to the 2D electron gas formation (polar catastrophe, cation interdiffusion, surface reactions and polarity-induced defects). Then, we thoroughly describe the experimental procedure to obtain such heterostructures, including a comprehensive guide on the surface treatment of SrTiO3 single crystals, the pulsed laser deposition growth of ultra-thin LaAlO3 films and magnetron sputtering. In addition, we elaborate on the two main techniques used to evaluate the interfacial properties, X-ray photoelectron spectroscopy and magnetotransport, while showing some results for LaAlO3/SrTiO3 samples. Lastly, we show how a thin deposition of a metallic layer on top of LaAlO3/SrTiO3 can drastically change the interfacial properties, by reducing (if the metal is reactive) or increasing (for noble metals) the critical thickness for conduction. We end this chapter by giving a blueprint that describes how a 2D electron gas can be created in other oxide systems. In the third chapter we investigate spin-tocharge conversion phenomena. We start by giving an overview on experimental observations of Rashba 2D electron gases, as well as spin-to-charge current conversion through the inverse Edelstein effect in semiconductor quantum wells, topological insulators and oxide-based systems. Then, we thoroughly introduce spin pumping, a technique used to generate pure spin currents. Results for spin-to-charge current conversion in the LaAlO3/SrTiO3 and metal-capped SrTiO3 systems are shown, accompanied by an interpretation of the large and tunable conversion efficiency. For the metal-capped SrTiO3 case, angle-resolved photoemission spectroscopy and notions of electronic band mixing and topology are introduced to describe the extremely large efficiency. In the last chapter, we show additional experiments performed on the LaAlO3/SrTiO3 system regarding anisotropic and unidirectional magnetoresistance, while reviewing the scarce bibliography on these effects in 2D electron gases. After that, we introduce a recently discovered effect, the unidirectional spin Hall magnetoresistance, and develop a simple conceptual model for an analogous effect in 2D electron gases: the unidirectional Edesltein magnetoresistance. This effect is based on the expected strong charge-to-spin conversion in 2D electrons gas, and the interaction of the generated spin currents with an adjacent ferromagnet. We finish by very briefly showing preliminary experiments in NiFe/ LaAlO3/SrTiO3 heterostructures.Ce travail présente l’étude de la conversion courant de spin en courant de charge dans les gaz d’électrons bidimensionnels à base de SrTiO3. Nous commençons par une présentation des concepts de base de la spintronique : le spin, une définition du courant de spin et le comportement des spins dans des matériaux, les principales conséquences de la relation entre les courants de charge et de spin dans différents matériaux, et comment un courant de charge peut être converti en un courant de spin (et vice versa). Dans des scénarios spécifiques, la physique de l’interconversion suit des considérations de symétrie particulières dans le cadre des effets de Dressllehaus et de Rashba, qui expliquent l’interconversion du courant de charge/spin dans les gaz d’électrons 2D via l’effet direct et inverse d’Edelstein. Dans le deuxième chapitre, nous présentons le principal matériau utilisé dans cette thèse: le titanate de strontium (SrTiO3). Après avoir analysé ses principales caractéristiques, nous explorons le gaz d’électrons 2D présent dans le système LaAlO3/SrTiO3. Nous discutons en détail de l’origine de la conductivité interfaciale entre ces deux isolateurs, l’épaisseur critique de conduction de 4 mailles de LaAlO3 et des principaux mécanismes conduisant à la formation du gaz électronique 2D (catastrophe polaire, interdiffusion de cation, réactions à la surface et défauts induits par la polarité). Ensuite, nous décrivons en détail la procédure expérimentale pour obtenir des hétérostructures de LaAlO3/SrTiO3: le traitement de surface des monocristaux de SrTiO3, la croissance par ablation laser pulsé de films ultra-minces de LaAlO3, et la pulvérisation cathodique. Nous introduisons les deux techniques principales utilisées pour évaluer les propriétés interfaciales, la spectroscopie photoélectronique de rayons X (XPS) et le magnétotransport, avec quelques résultats pour les échantillons de LaAlO3/SrTiO3. Enfin, nous montrons comment un mince dépôt d’une couche métallique sur LaAlO3/SrTiO3 peut modifier radicalement les propriétés interfaciales en réduisant (si le métal est réactif et possède un travail de sortie inférieur à une valeur critique) ou en augmentant (pour les métaux nobles) l’épaisseur critique de la conduction interfacial. Pour conclure ce chapitre, nous proposons un modèle qui décrit comment un gaz d’électrons 2D peut être créé dans d’autres systèmes à base d’oxydes complexes. Dans le troisième chapitre, nous étudions les phénomènes de conversion spin/charge. Nous commençons par un état de l’art de la littérature concernant des observations expérimentales des gaz d’électrons Rashba 2D, ainsi que de la conversion du courant spin-à-charge par l’effet Edelstein inverse dans les puit de potentiel à base de semi-conducteurs, les isolants topologiques et les systèmes à base d’oxydes. Ensuite, nous introduisons le pompage de spin, une technique utilisée pour générer des courants de spin purs. Les résultats de la conversion du courant spinà-charge dans les systèmes LaAlO3/SrTiO3 et metal/SrTiO3 sont présentés, accompagnés d’une interprétation de la géante et ajustable con-version spin/charge. Dans le cas d’échantillons composés par metal/SrTiO3 , la spectroscopie photoélectronique résolue en angle (ARPES) et les notions de mélange de bande électronique et de topologie sont introduites pour justifier la conversion charge/spin extrêmement élevé. Dans le dernier chapitre, nous montrons des expériences supplémentaires réalisées sur le système LaAlO3/SrTiO3 en ce qui concerne la magnétorésistance anisotrope et unidirectionnelle [...

Spin–Charge Interconversion in KTaO 3 2D Electron Gases

International audienceOxide interfaces exhibit a broad range of physical effects stemming from broken inversion symmetry. In particular, they can display non-reciprocal phenomena when time reversal symmetry is also broken, e.g., by the application of a magnetic field. Examples include the direct and inverse Edelstein effects (DEE, IEE) that allow the interconversion between spin currents and charge currents. The DEE and IEE have been investigated in interfaces based on the perovskite SrTiO$_3$ (STO), albeit in separate studies focusing on one or the other. The demonstration of these effects remains mostly elusive in other oxide interface systems despite their blossoming in the last decade. Here, we report the observation of both the DEE and IEE in a new interfacial two-dimensional electron gas (2DEG) based on the perovskite oxide KTaO$_3$. We generate 2DEGs by the simple deposition of Al metal onto KTaO$_3$ single crystals, characterize them by angle-resolved photoemission spectroscopy and magnetotransport, and demonstrate the DEE through unidirectional magnetoresistance and the IEE by spin-pumping experiments. We compare the spin-charge interconversion efficiency with that of STO-based interfaces, relate it to the 2DEG electronic structure, and give perspectives for the implementation of KTaO$_3$ 2DEGs into spin-orbitronic devices