Monopole-like orbital-momentum locking and the induced orbital transport in topological chiral semimetals

The interplay between chirality and topology nurtures many exotic electronic properties. For instance, topological chiral semimetals display multifold chiral fermions that manifest nontrivial topological charge and spin texture. They are an ideal playground for exploring chirality-driven exotic physical phenomena. In this work, we reveal a monopole-like orbital-momentum locking texture on the three-dimensional Fermi surfaces of topological chiral semimetals with B20 structures (e.g., RhSi and PdGa). This orbital texture enables a large orbital Hall effect (OHE) and a giant orbital magnetoelectric (OME) effect in the presence of current flow. Different enantiomers exhibit the same OHE which can be converted to the spin Hall effect by spin-orbit coupling in materials. In contrast, the OME effect is chirality-dependent and much larger than its spin counterpart. Our work reveals the crucial role of orbital texture for understanding OHE and OME effects in topological chiral semimetals and paves the path for applications in orbitronics, spintronics, and enantiomer recognition

Berry curvature induced anomalous Hall conductivity in the magnetic topological oxide double perovskite Sr₂FeMoO₆

Oxide materials exhibit several structural, magnetic, and electronic properties. Their stability under ambient conditions, easy synthesis, and high transition temperatures provide such systems with an ideal ground for realizing topological properties and real-life technological applications. However, experimental evidence of topological states in oxide materials is rare. In this paper, we have synthesized single crystals of oxide double perovskite Sr2FeMoO6 and revealed its topological nature by investigating its structural, magnetic, and electronic properties. We observed that the system crystallized in the cubic space group Fm3¯m, which is a half-metallic ferromagnet. Transport measurements show an anomalous Hall effect (AHE), and it is evident that the Hall contribution originates from the Berry curvature. Assuming a shift of the Fermi energy toward the conduction band, the contribution of the AHE is enhanced owing to the presence of a gapped nodal line. This paper can be used to explore and realize the topological properties of bulk oxide systems. © 2022 authors. Published by the American Physical Society

La importancia de los trabajos de campo en la confección del modelo del terreno para aplicaciones en ecología

The main aim of this paper is to highlight the extraordinary importance of field surveying for carrying out certain ecological models in which habitats of vegetal communities are conditioned by land elevation. An illustrated case study in the wetlands of Doñana National Park shows the key role of Field Inspections, particularly since morphology (altitude attribute) is one of the first factors that condition the superficial expansion of the main vegetal perennial communities within the wetland system.Se pretende demostrar la extraordinaria incidencia que tienen los trabajos de campo en la confección de determinados modelos ecológicos, en los que el relieve del terreno condiciona el hábitat de sus principales comunidades vegetales. Se ilustra esta hipótesis con un ejemplo extraído de la marisma del Parque Nacional de Doñana, donde su morfología es uno de los factores principales que configura la fisonomía del paisaje vegetal, al condicionar la expansión de las principales agrupaciones vegetales perennes del sistema marismeño

A New Three-Dimensional Subsulfide Ir₂In₈S with Dirac Semimetal Behavior

Dirac and Weyl semimetals host exotic quasiparticles with unconventional transport properties, such as high magnetoresistance and carrier mobility. Recent years have witnessed a huge number of newly predicted topological semimetals from existing databases; however, experimental verification often lags behind such predictions. Common reasons are synthetic difficulties or the stability of predicted phases. Here, we report the synthesis of the Type-II Dirac semimetal Ir2In8S, an air-stable compound with a new structure type. This material has two Dirac crossings in its electronic structure along the Γ-Z direction of the Brillouin zone. We further show that Ir2In8S has a high electron carrier mobility of ~10,000 cm2/Vs at 1.8 K, and a large, non-saturating transverse magnetoresistance of ~6000% at 3.34 K in a 14 T applied field. Shubnikov de-Haas oscillations reveal several small Fermi pockets and the possibility of a nontrivial Berry phase. With its facile crystal growth, novel structure type, and striking electronic structure, Ir2In8S introduces a new material system to study topological semimetals and enable advances in the field of topological materials

Unconventional Charge-to-Spin Conversion in Graphene/MoTe2 van der Waals Heterostructures

Spin-charge interconversion (SCI) is a central phenomenon to the development of spintronic devices from materials with strong spin-orbit coupling (SOC). In the case of materials with high crystal symmetry, the only allowed SCI processes are those where the spin-current, charge-current, and spin-polarization directions are orthogonal to each other. Consequently, standard SCI experiments are designed to maximize the signals arising from the SCI processes with conventional mutually orthogonal geometry. However, in low-symmetry materials, certain nonorthogonal SCI processes are also allowed. Since the standard SCI experiment is limited to charge current flowing only in one direction in the SOC material, certain allowed SCI configurations remain unexplored. Here, we perform a thorough SCI study in a graphene-based lateral spin valve combined with low-symmetry MoTe2. Due to a very low contact resistance between the two materials, we can detect SCI signals using both a standard configuration, where the charge current is applied along MoTe2, and a recently introduced [three-dimensional- (3D) current] configuration, where the charge-current flow can be controlled in three directions within the heterostructure. As a result, we observe three different SCI components, one orthogonal and two nonorthogonal, adding valuable insight into the SCI processes in low-symmetry materials. The large SCI signals obtained at room temperature, along with the versatility of the 3D-current configuration, provide feasibility and flexibility to the design of the next generation of spin-based devices.This work is supported by the Spanish MICINN under Projects No. RTI2018-094861-B-I00, No. PGC2018-101988-B-C21, No. PID2019-109905GB-C21, No. MAT2017-88377-C2-2-R, and the Maria de Maeztu Units of Excellence Programme (Grants No. MDM-2016-0618 and No. CEX2020-001038-M); the “Valleytronics” Intel Science Technology Center; the Gipuzkoa Regional Council under Projects No. 2021-CIEN-000037-01 and No. 2021-CIEN-000070-01; and the European Union H2020 under the Marie Sklodowska-Curie Actions (Grants No. 0766025-QuESTech and No. 794982-2DSTOP). N.O. thanks the Spanish MICINN for support from a Ph.D. fellowship (Grant No. BES-2017-07963). J.I.-A. acknowledges support from the “Juan de la Cierva-Formación” program by the Spanish MICINN (Grant No. FJC2018-038688-I) for a postdoctoral fellowship. R.C. acknowledges funding from Generalitat Valenciana through Grant No. CIDEGENT/2018/004 M.G.V. and I.R. thanks support from the Spanish MICINN (grant PID2019-109905GBC21), the German Research Foundation DFG (grant nr. GA3314/1-1-FOR 5249 QUAST) and the European Research Council ERC (Grant No. 101020833)

Frutillas y calafates de la Patagonia Argentina: Avances en la determinación de compuestos fenólicos y actividad antioxidante

Muchos frutos de pequeño tamaño, conocidos como “berries”, han sido domesticados y hoy ocupan un lugar protagónico en la dieta de millones de personas que los eligen por su sabor y propiedades antioxidantes. Dentro de nuestro patrimonio biocultural en la patagonia argentina se encuentran los calafates o michays (Berberis microphylla y B. darwinii) y la frutilla nativa (Fragaria chiloensis sp. chiloensis). Tomando estas tres especies, nos propusimos (i) caracterizar su perfil de compuestos fenólicos y la capacidad antioxidante de frutos provenientes de poblaciones naturales de la patagonia argentina, y (ii) comparar la composición química y potencial antioxidante de frutos comerciales y silvestres, bajo iguales condiciones de cultivo, focalizándonos en la frutilla como caso de estudio. Para el primer objetivo, se recolectaron frutos maduros en distintos sitios del Parque Nacional Nahuel Huapi y alrededores. A estos, se les midió su capacidad antioxidante mediante ensayos espectrofotométricos y se utilizó cromatografía líquida de alta eficiencia para separar e identificar los compuestos fenólicos. Para el segundo objetivo, se obtuvieron ejemplares de F. chiloensis de tres poblaciones silvestres y de dos variedades comerciales de F. x ananassa (San Andreas y Albión), las cuales fueron cultivadas en jardín común siguiendo las prácticas de los productores locales. Se evaluó la actividad antioxidante mediante la técnica que utiliza el 2,2-difenil-1-picrilhidrazilo, la composición de tres grupos de compuestos fenólicos bajo técnicas espectrofotométricas y el contenido de ácido elágico, cianidina-3-glucósido y catequina mediante cromatografía líquida. Los frutos nativos de las poblaciones naturales poseen un gran potencial antioxidante, siendo esta propiedad mayor para B. microphylla. En cuanto a la composición química, se encontró un perfil más complejo para los Berberis, por ejemplo, a nivel de las antocianinas estas presentaron 10 compuestos mientras que en F. chiloensis se identificaron tentativamente 4. Por otro lado, en el ensayo a campo bajo condiciones de jardín común, las frutillas nativas se destacaron por su mayor actividad antioxidante y su mayor contenido de ácido elágico, mientras que las frutillas comerciales obtuvieron un mayor contenido de antocianinas totales. Frutillas nativas y comerciales presentaron niveles similares de fenoles y flavonoides totales. Por lo tanto, en este trabajo se concretó el primer ensayo a campo de crecimiento y cosecha de frutillas nativas y comerciales. Este último evidenció que la frutilla nativa expresa un perfil diferencial de compuestos fenólicos comparada con la frutilla comercial. Además, se concluye que los calafates y la frutilla nativa de la patagonia son especies con un gran potencial como alimentos funcionales

Controllable orbital angular momentum monopoles in chiral topological semimetals

The emerging field of orbitronics aims at generating and controlling currents of electronic orbital angular momentum (OAM) for information processing. Structurally chiral topological crystals could be particularly suitable orbitronic materials because they have been predicted to host topological band degeneracies in reciprocal space that are monopoles of OAM. Around such a monopole, the OAM is locked isotopically parallel or antiparallel to the direction of the electron's momentum, which could be used to generate large and controllable OAM currents. However, OAM monopoles have not yet been directly observed in chiral crystals, and no handle to control their polarity has been discovered. Here, we use circular dichroism in angle-resolved photoelectron spectroscopy (CD-ARPES) to image OAM monopoles in the chiral topological semimetals PtGa and PdGa. Moreover, we also demonstrate that the polarity of the monopole can be controlled via the structural handedness of the host crystal by imaging OAM monopoles and anti-monopoles in the two enantiomers of PdGa, respectively. For most photon energies used in our study, we observe a sign change in the CD-ARPES spectrum when comparing positive and negative momenta along the light direction near the topological degeneracy. This is consistent with the conventional view that CD-ARPES measures the projection of the OAM monopole along the photon momentum. For some photon energies, however, this sign change disappears, which can be understood from our numerical simulations as the interference of polar atomic OAM contributions, consistent with the presence of OAM monopoles. Our results highlight the potential of chiral crystals for orbitronic device applications, and our methodology could enable the discovery of even more complicated nodal OAM textures that could be exploited for orbitronics.Comment: 16 pages, 8 figure

Citizen Science to Raise Antimicrobial Resistance Awareness in the Community: The MicroMundo Project in Spain and Portugal

Antimicrobial resistance (AMR) poses a global threat to human, animal and environmental health. Among the multidisciplinary tasks aimed at collectively tackling the AMR crisis, surveillance, research and education stand as major priorities. Based on a crowdsourcing research strategy, the MicroMundo project, a partner of the Tiny Earth initiative in Spain and Portugal, has been developed and consolidated with success in the academic environment. The objectives are focused on promoting research and, especially, on bringing knowledge of One Health and microbiology concepts, as well as AMR awareness to the community. Following a service-learning approach, MicroMundo integrates university and secondary/high school students in a citizen science-based research project to collectively isolate microorganisms with the potential to produce new antibiotics from soil environments. Over the last 7 years, 32 MicroMundo hubs operating across 31 different Portuguese and Spanish universities have recruited thousands of teenagers in this quest. Here we review the outcome of this unprecedented effort from a scientific and an educational perspective

Leaf water potential and sap flow as indicators of water stress in Crimson ‘seedless’ grapevines under different irrigation strategies

Vitis vinifera L. cv. Crimson Seedless is a late season red table grape developed in 1989, with a high market value and increasingly cultivated under protected environments to extend the availability of seedless table grapes into the late fall. The purpose of this work was to evaluate leaf water potential and sap flow as indicators of water stress in Crimson Seedless vines under standard and reduced irrigation strategy, consisting of 70 % of the standard irrigation depth. Additionally, two sub-treatments were applied, consisting of normal irrigation throughout the growing season and a short irrigation induced stress period between veraison and harvest. Leaf water potential measurements coherently signaled crop-available water variations caused by different irrigation treatments, suggesting that this plant-based method can be reliably used to identify water-stress conditions. The use of sap flow density data to establish a ratio based on a reference ‘well irrigated vine’ and less irrigated vines can potentially be used to signal differences in the transpiration rates, which may be suitable for improving irrigation management strategies while preventing undesirable levels of water stress. Although all four irrigation strategies resulted in the production of quality table grapes, significant differences (p ≤ 0.05) were found in both berry weight and sugar content between the standard irrigation and reduced irrigation treatments. Reduced irrigation increased slightly the average berry size as well as sugar content and technical maturity index. The 2-week irrigation stress period had a negative effect on these parameters