New Moiré Landscapes for Atomic Spins

The interactions of the spins of single atoms with a substrate can be controlled via the moiré lattice created by depositing a 2D material on top of the substrate

Flow blurring atomization of Poly(ethylene oxide) solutions below the coil overlap concentration

Atomization of polymer solutions has important technological implications across many fields. Here, we investigated the atomization dynamics of diluted, polymer solutions using Flow Blurring (FB) technology. Aqueous solutions of poly(ethylene oxide) [PEO] of viscosity-averaged molecular weight in the range 100000 g/mol – 4000000 g/mol and varying concentrations were sprayed with a FB atomizer having an orifice diameter (D) of 700μm and a liquid feed-tube-to-orifice separation (H) of 100μm. The solutions belong to the dilute regime, where polymer coil overlap does not occur, that is φ= [Formula presented] <φcrit (Modesto-López, Pérez-Arjona, & Gañán-Calvo, 2019). Shear viscosity measurements indicated that the solutions had viscosities of the order of that of the solvent and exhibited a Newtonian-like behavior. However, during the atomization, and due to the relatively high shear stress induced in the atomizer, the solutions exhibit extensional rheology, which most likely arises from the stretching of the polymer chains in-flight. Although initially the atomization resulted in formation of filaments, these broke up into droplets at relatively short distances from the atomizer discharge orifice as elucidated by images from ultra-high speed videos. The phenomenon is in contrast with that observed in FB-based atomization of semi-diluted polymer solutions with concentrations larger than the polymer coil overlap concentration, c∗. FB atomization of the diluted solutions resulted in a decrease in droplet size with increasing the gas-to-liquid mass ratio (GLR). The approach herein aims at understanding the droplet formation dynamics of viscoelastic, polymer solutions with FB, for applications in large-scale synthesis of materialsMinisterio de Economía, Industria y Competitividad DPI2016-78887-C3-1-

Dynamic bonding of metallic nanocontacts: Insights from experiments and atomistic simulations

The conductance across an atomically narrow metallic contact can be measured by using scanning tunneling microscopy. In certain situations, a jump in the conductance is observed right at the point of contact between the tip and the surface, which is known as “jump to contact” (JC). Such behavior provides a way to explore, at a fundamental level, how bonding between metallic atoms occurs dynamically. This phenomenon depends not only on the type of metal but also on the geometry of the two electrodes. For example, while some authors always find JC when approaching two atomically sharp tips of Cu, others find that a smooth transition occurs when approaching a Cu tip to an adatom on a flat surface of Cu. In an attempt to show that all these results are consistent, we make use of atomistic simulations; in particular, classical molecular dynamics together with density functional theory transport calculations to explore a number of possible scenarios. Simulations are performed for two different materials: Cu and Au in a [100] crystal orientation and at a temperature of 4.2 K. These simulations allow us to study the contribution of short- and long-range interactions to the process of bonding between metallic atoms, as well as to compare directly with experimental measurements of conductance, giving a plausible explanation for the different experimental observations. Moreover, we show a correlation between the cohesive energy of the metal, its Young's modulus, and the frequency of occurrence of a jump to contact.W. Dednam acknowledges support from the National Research Foundation of South Africa through the Scarce Skills Masters scholarship funding programme (Grant Unique Number 92138). This work is supported by the Generalitat Valenciana through Grant Reference PROMETEO2012/011 and MINECO under Grant No. FIS2013-47328, by European Union structural funds and the Comunidad de Madrid Programs S2013/MIT-3007 and P2013/MIT-2850. This work is also part of the research programme of the Foundation for Fundamental Research on Matter (FOM), which is financially supported by the Netherlands Organisation for Scientific Research (NWO)

Out-of-plane spin-to-charge conversion at low temperatures in graphene/MoTe2_2 heterostructures

Multi-directional spin-to-charge conversion - in which spin polarizations with different orientations can be converted into a charge current in the same direction - has been demonstrated in low-symmetry materials and interfaces. This is possible because, in these systems, spin to charge conversion can occur in unconventional configurations in which spin polarization and charge current where charge current, spin current and polarization do not need to be mutually orthogonal. Here, we explore, in the low temperature regime, the spin-to-charge conversion in heterostructures of graphene with the low-symmetry 1T' phase of MoTe$_2$. First, we observe the emergence of charge conversion for out-of-plane spins at temperatures below 100 K. This unconventional component is allowed by the symmetries of both MoTe$_2$ and graphene and likely arises from spin Hall effect in the spin-orbit proximitized graphene. Moreover, we examine the low-temperature evolution of non-local voltage signals arising from the charge conversion of the two in-plane spin polarizations, which have been previously observed at higher temperature. As a result, we report omni-directional spin-to-charge conversion - for all spin polarization orientations - in graphene/MoTe${_2}$ heterostructures at low temperatures.Comment: 7 pages, 4 figure

Directional bonding explains the high conductance of atomic contacts in bcc metals

Atomic-sized contacts of iron, created in scanning tunneling microscope break junctions, present unusually high values of conductance compared to other metals. This result is counterintuitive since, at the nanoscale, body-centered-cubic metals are expected to exhibit lower coordination than face-centered-cubic metals. In this work we first perform classical molecular dynamics simulations of the contact rupture, using two different interatomic potentials. The first potential is isotropic, and produces mostly single-atom prerupture contacts. The second potential accounts for the directional bonding in the materials, and produces mostly highly coordinated prerupture structures, generally consisting of more than one atom in contact. To compare the two different types of structures with experiments, we use them as input to density functional theory electronic transport calculations of the conductance. We find that the highly coordinated structures, obtained from the anisotropic potential, yield higher conductances which are statistically in better agreement with those measured for body-centered-cubic iron. We thus conclude that the directional bonding plays an important role in body-centered-cubic metals.This work was supported by the Generalitat Valenciana through PROMETEO2017/139 and GENT (CDEIGENT2018/028), the Spanish government through Grants No. MAT2016-78625-C2-1-P and No. FIS2016-80434-P, and the Spanish Ministry of Science and Innovation, through the “María de Maeztu” Programme for Units of Excellence in R&D (CEX2018-000805-M), by Comunidad Autónoma de Madrid through Grant No. S2018/NMT-4321 (NanomagCOST-CM), by the Fundación Ramón Areces, and by the European Union Graphene Flagship under Grant No. 604391

Large Biaxial Compressive Strain Tuning of Neutral and Charged Excitons in Single-Layer Transition Metal Dichalcogenides

The absorption and emission of light in single-layer transition metal dichalcogenides are governed by the formation of excitonic quasiparticles. Strain provides a powerful technique to tune the optoelectronic properties of two-dimensional materials and thus to adjust their exciton energies. The effects of large compressive strain in the optical spectrum of two-dimensional (2D) semiconductors remain rather unexplored compared to those of tensile strain, mainly due to experimental constraints. Here, we induced large, uniform, biaxial compressive strain (∼1.2%) by cooling, down to 10 K, single-layer WS2, MoS2, WSe2, and MoSe2 deposited on polycarbonate substrates. We observed a significant strain-induced modulation of neutral exciton energies, with blue shifts up to 160 meV, larger than in any previous experiments. Our results indicate a remarkably efficient transfer of compressive strain, demonstrated by gauge factor values exceeding previous results and approaching theoretical expectations. At low temperatures, we investigated the effect of compressive strain on the resonances associated with the formation of charged excitons. In WS2, a notable reduction of gauge factors for charged compared to neutral excitons suggests an increase in their binding energy, which likely results from the effects of strain added to the influence of the polymeric substrate.The authors acknowledge funding from the Generalitat Valenciana through grants IDIFEDER/2020/005 and IDIFEDER/2021/016 and support from the Plan Gen-T of Excellence for M.R.C (CideGenT2018004) and from the Spanish MCINN through grants PLASTOP PID2020-119124RB-I00, TED2021-131641B-C43, PID2020-115566RB-I00, TED2021-132267B-I00, and PID2020-112811GB-I00. This work was funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 755655, ERC-StG 2017 project 2D-TOPSENSE). The authors also acknowledge funding from the EU FLAG-ERA project To2Dox (JTC-2019-009) and the Comunidad de Madrid through the CAIRO-CM project (Y2020/NMT-6661). H.L. acknowledges support from China Scholarship Council (CSC) under grant no. 201907040070. D.G.-M. thanks the Maria Zambrano Program at the University of Alicante founded by the European Union-Next Generation EU. R.D’A. acknowledges support from the Grant No. IT1453- 22 “Grupos Consolidados UPV/EHU del Gobierno Vasco”

Role of Rhinovirus C in Apparently Life-Threatening Events in Infants, Spain

To assess whether infants hospitalized after an apparently life-threatening event had an associated respiratory virus infection, we analyzed nasopharyngeal aspirates from 16 patients. Nine of 11 infants with positive virus results were infected by rhinoviruses. We detected the new genogroup of rhinovirus C in 6 aspirates

Influence of the ovine genital tract microbiota on the species artificial insemination outcome. A pilot study in commercial sheep farms

To date, there is a lack of research into the vaginal and sperm microbiome and its bearing on artificial insemination (AI) success in the ovine species. Using hypervariable regions V3–V4 of the 16S rRNA, we describe, for the first time, the combined effect of the ovine microbiome of both females (50 ewes belonging to five herds) and males (five AI rams from an AI center) on AI outcome. Differences in microbiota abundance between pregnant and non-pregnant ewes and between ewes carrying progesterone-releasing intravaginal devices (PRID) with or without antibiotic were tested at different taxonomic levels. The antibiotic treatment applied with the PRID only altered Streptobacillus genus abundance, which was significantly lower in ewes carrying PRID with antibiotic. Mageebacillus, Histophilus, Actinobacilllus and Sneathia genera were significantly less abundant in pregnant ewes. In addition, these genera were more abundant in two farms with higher AI failure. Species of these genera such as Actinobacillus seminis and Histophilus somni have been associated with reproductive disorders in the ovine species. These genera were not present in the sperm samples of AI rams, but were found in the foreskin samples of rams belonging to herd 2 (with high AI failure rate) indicating that their presence in ewes’ vagina could be due to prior transmission by natural mating with rams reared in the herd

The Kondo effect in ferromagnetic atomic contacts

Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk, electronic conduction in these materials takes place mainly through the $s$ and $p$ electrons, whereas the magnetic moments are mostly in the narrow $d$-electron bands, where they tend to align. This general picture may change at the nanoscale because electrons at the surfaces of materials experience interactions that differ from those in the bulk. Here we show direct evidence for such changes: electronic transport in atomic-scale contacts of pure ferromagnets (iron, cobalt and nickel), despite their strong bulk ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of local magnetic moments by the conduction electrons below a characteristic temperature. The Kondo effect creates a sharp resonance at the Fermi energy, affecting the electrical properties of the system;this appears as a Fano-Kondo resonance in the conductance characteristics as observed in other artificial nanostructures. The study of hundreds of contacts shows material-dependent lognormal distributions of the resonance width that arise naturally from Kondo theory. These resonances broaden and disappear with increasing temperature, also as in standard Kondo systems. Our observations, supported by calculations, imply that coordination changes can significantly modify magnetism at the nanoscale. Therefore, in addition to standard micromagnetic physics, strong electronic correlations along with atomic-scale geometry need to be considered when investigating the magnetic properties of magnetic nanostructures.Comment: 7 pages, 5 figure

A smart material for the in situ detection of mercury in fish

We have developed a new fluorogenic polymer capable of detecting the presence of mercury contamination in fish samples. The modified polymer emits blue light when irradiated with UV light proportional to the quantity of mercury, as MeHg+ or Hg2+, present in fish. The quantitative relation between the concentration of mercury in fish and the increase of fluorescence in the polymer in contact with fish samples was confirmed, giving rise to quick and reliable results in the measurements of the presence of mercury in fish using a portable fluorogenic polymeric probe.theMinisterio de Economı´a y Competitividad, Spain, and Fondo Europeo de Desarrollo Regional (FEDER) (Projects CTQ2015-71353-R and MAT2014-54137-R), Junta de Castilla y Leo´n, Consejerı´a de Educacio´n y Cultura y Fondo Social Europeo (Projects BU051U16 and BU061U16), and the European Commission, Seventh Framework Programme (Project SNIFFER FP7-SEC-2012-312411