Uncovering the Lowest Thickness Limit for Room-Temperature Ferromagnetism of Cr1.6Te2.

Metallic ferromagnetic transition metal dichalcogenides have emerged as important building blocks for scalable magnetic and memory applications. Downscaling such systems to the ultrathin limit is critical to integrate them into technology. Here, we achieved layer-by-layer control over the transition metal dichalcogenide Cr1.6Te2 by using pulsed laser deposition, and we uncovered the minimum critical thickness above which room-temperature magnetic order is maintained. The electronic and magnetic structures are explored experimentally and theoretically, and it is shown that the films exhibit strong in-plane magnetic anisotropy as a consequence of large spin-orbit effects. Our study elucidates both magnetic and electronic properties of Cr1.6Te2 and corroborates the importance of intercalation to tune the magnetic properties of nanoscale materials' architectures.

Weyl spin-momentum locking in a chiral topological semimetal.

Spin-orbit coupling in noncentrosymmetric crystals leads to spin-momentum locking - a directional relationship between an electron's spin angular momentum and its linear momentum. Isotropic orthogonal Rashba spin-momentum locking has been studied for decades, while its counterpart, isotropic parallel Weyl spin-momentum locking has remained elusive in experiments. Theory predicts that Weyl spin-momentum locking can only be realized in structurally chiral cubic crystals in the vicinity of Kramers-Weyl or multifold fermions. Here, we use spin- and angle-resolved photoemission spectroscopy to evidence Weyl spin-momentum locking of multifold fermions in the chiral topological semimetal PtGa. We find that the electron spin of the Fermi arc surface states is orthogonal to their Fermi surface contour for momenta close to the projection of the bulk multifold fermion at the Γ point, which is consistent with Weyl spin-momentum locking of the latter. The direct measurement of the bulk spin texture of the multifold fermion at the R point also displays Weyl spin-momentum locking. The discovery of Weyl spin-momentum locking may lead to energy-efficient memory devices and Josephson diodes based on chiral topological semimetals.

Signatures of a surface spin-orbital chiral metal.

The relation between crystal symmetries, electron correlations and electronic structure steers the formation of a large array of unconventional phases of matter, including magneto-electric loop currents and chiral magnetism1-6. The detection of such hidden orders is an important goal in condensed-matter physics. However, until now, non-standard forms of magnetism with chiral electronic ordering have been difficult to detect experimentally7. Here we develop a theory for symmetry-broken chiral ground states and propose a methodology based on circularly polarized, spin-selective, angular-resolved photoelectron spectroscopy to study them. We use the archetypal quantum material Sr2RuO4 and reveal spectroscopic signatures that, despite being subtle, can be reconciled with the formation of spin-orbital chiral currents at the surface of the material8-10. As we shed light on these chiral regimes, our findings pave the way for a deeper understanding of ordering phenomena and unconventional magnetism.

Genetic engineering employing MPB70 and its promoter enables efficient secretion and expression of foreign antigen in bacillus Calmette Guérin (BCG) Tokyo.

Vaccination is an important factor in public health. The recombinant bacillus Calmette Guérin (rBCG) vaccine, which expresses foreign antigens, is expected to be a superior vaccine against infectious diseases. Here, we report a new recombination platform in which the BCG Tokyo strain is transformed with nucleotide sequences encoding foreign protein fused with the MPB70 immunogenic protein precursor. By RNA-sequencing, mpb70 was found to be the most transcribed among all known genes of BCG Tokyo. Small oligopeptide, namely, polyhistidine tag, was able to be expressed in and secreted from rBCG through a process in which polyhistidine tag fused with intact MPB70 were transcribed by an mpb70 promoter. This methodology was applied to develop an rBCG expressing the receptor binding domain (RBD) of severe acute respiratory syndrome coronavirus 2. Immunoblotting images and mass spectrometry data showed that RBD was also secreted from rBCG. Sera from mice vaccinated with the rBCG showed a tendency of weak neutralizing capacity. The secretion was retained even after a freeze-drying process. The freeze-dried rBCG was administered to and recovered from mice. Recovered rBCG kept secreting RBD. Collectively, our recombination platform offers stable secretion of foreign antigens and can be applied to the development of practical rBCGs.

Observation of Termination-Dependent Topological Connectivity in a Magnetic Weyl Kagome Lattice.

Engineering surfaces and interfaces of materials promises great potential in the field of heterostructures and quantum matter designers, with the opportunity to drive new many-body phases that are absent in the bulk compounds. Here, we focus on the magnetic Weyl kagome system Co3Sn2S2 and show how for the terminations of different samples the Weyl points connect differently, still preserving the bulk-boundary correspondence. Scanning tunneling microscopy has suggested such a scenario indirectly, and here, we probe the Fermiology of Co3Sn2S2 directly, by linking it to its real space surface distribution. By combining micro-ARPES and first-principles calculations, we measure the energy-momentum spectra and the Fermi surfaces of Co3Sn2S2 for different surface terminations and show the existence of topological features depending on the top-layer electronic environment. Our work helps to define a route for controlling bulk-derived topological properties by means of surface electrostatic potentials, offering a methodology for using Weyl kagome metals in responsive magnetic spintronics.

Revealing the Hidden Spin-Polarized Bands in a Superconducting Tl Bilayer Crystal.

The interplay of spin-orbit coupling and crystal symmetry can generate spin-polarized bands in materials only a few atomic layers thick, potentially leading to unprecedented physical properties. In the case of bilayer materials with global inversion symmetry, locally broken inversion symmetry can generate degenerate spin-polarized bands, in which the spins in each layer are oppositely polarized. Here, we demonstrate that the hidden spins in a Tl bilayer crystal are revealed by growing it on Ag(111) of sizable lattice mismatch, together with the appearance of a remarkable phenomenon unique to centrosymmetric hidden-spin bilayer crystals: a novel band splitting in both spin and space. The key to success in observing this novel splitting is that the interaction at the interface has just the right strength: it does not destroy the original wave functions of the Tl bilayer but is strong enough to induce an energy separation.

Giant and Tunable Out-of-Plane Spin Polarization of Topological Antimonene.

Topological insulators are bulk insulators with metallic and fully spin-polarized surface states displaying Dirac-like band dispersion. Due to spin-momentum locking, these topological surface states (TSSs) have a predominant in-plane spin polarization in the bulk fundamental gap. Here, we show by spin-resolved photoemission spectroscopy that the TSS of a topological insulator interfaced with an antimonene bilayer exhibits nearly full out-of-plane spin polarization within the substrate gap. We connect this phenomenon to a symmetry-protected band crossing of the spin-polarized surface states. The nearly full out-of-plane spin polarization of the TSS occurs along a continuous path in the energy-momentum space, and the spin polarization within the gap can be reversibly tuned from nearly full out-of-plane to nearly full in-plane by electron doping. These findings pave the way to advanced spintronics applications that exploit the giant out-of-plane spin polarization of TSSs.

Nd:YAG infrared laser as a viable alternative to excimer laser: YBCO case study.

We report on the growth and characterization of epitaxial YBa[Formula: see text]Cu[Formula: see text]O[Formula: see text] (YBCO) complex oxide thin films and related heterostructures exclusively by Pulsed Laser Deposition (PLD) and using first harmonic Nd:Y[Formula: see text]Al[Formula: see text]O[Formula: see text] (Nd:YAG) pulsed laser source ([Formula: see text] = 1064  nm). High-quality epitaxial YBCO thin film heterostructures display superconducting properties with transition temperature [Formula: see text] 80 K. Compared with the excimer lasers, when using Nd:YAG lasers, the optimal growth conditions are achieved at a large target-to-substrate distance d. These results clearly demonstrate the potential use of the first harmonic Nd:YAG laser source as an alternative to the excimer lasers for the PLD thin film community. Its compactness as well as the absence of any safety issues related to poisonous gas represent a major breakthrough in the deposition of complex multi-element compounds in form of thin films.

Unveiling the Catalytic Potential of Topological Nodal-Line Semimetal AuSn4 for Hydrogen Evolution and CO2 Reduction.

In recent years, the correlation between the existence of topological electronic states in materials and their catalytic activity has gained increasing attention, due to the exceptional electron conductivity and charge carrier mobility exhibited by quantum materials. However, the physicochemical mechanisms ruling catalysis with quantum materials are not fully understood. Here, we investigate the chemical reactivity, ambient stability, and catalytic activity of the topological nodal-line semimetal AuSn4. Our findings reveal that the surface of AuSn4 is prone to oxidation, resulting in the formation of a nanometric SnO2 skin. This surface oxidation significantly enhances the material's performance as a catalyst for the hydrogen evolution reaction in acidic environments. We demonstrate that the peculiar atomic structure of oxidized AuSn4 enables the migration of hydrogen atoms through the Sn-O layer with a minimal energy barrier of only 0.19 eV. Furthermore, the Volmer step becomes exothermic in the presence of Sn vacancies or tin-oxide skin, as opposed to being hindered in the pristine sample, with energy values of -0.62 and -1.66 eV, respectively, compared to the +0.46 eV energy barrier in the pristine sample. Our model also suggests that oxidized AuSn4 can serve as a catalyst for the hydrogen evolution reaction in alkali media. Additionally, we evaluate the material's suitability for the carbon dioxide reduction reaction, finding that the presence of topologically protected electronic states enhances the migration of hydrogen atoms adsorbed on the catalyst to carbon dioxide.

Discovery of a Magnetic Dirac System with a Large Intrinsic Nonlinear Hall Effect.

Magnetic materials exhibiting topological Dirac fermions are attracting significant attention for their promising technological potential in spintronics. In these systems, the combined effect of the spin-orbit coupling and magnetic order enables the realization of novel topological phases with exotic transport properties, including the anomalous Hall effect and magneto-chiral phenomena. Herein, we report experimental signature of topological Dirac antiferromagnetism in TaCoTe2 via angle-resolved photoelectron spectroscopy and first-principles density functional theory calculations. In particular, we find the existence of spin-orbit coupling-induced gaps at the Fermi level, consistent with the manifestation of a large intrinsic nonlinear Hall conductivity. Remarkably, we find that the latter is extremely sensitive to the orientation of the Néel vector, suggesting TaCoTe2 as a suitable candidate for the realization of non-volatile spintronic devices with an unprecedented level of intrinsic tunability.

Terahertz Nonlinear Hall Rectifiers Based on Spin-Polarized Topological Electronic States in 1T-CoTe2.

The zero-magnetic-field nonlinear Hall effect (NLHE) refers to the second-order transverse current induced by an applied alternating electric field; it indicates the topological properties of inversion-symmetry-breaking crystals. Despite several studies on the NLHE induced by the Berry-curvature dipole in Weyl semimetals, the direct current conversion by rectification is limited to very low driving frequencies and cryogenic temperatures. The nonlinear photoresponse generated by the NLHE at room temperature can be useful for numerous applications in communication, sensing, and photodetection across a high bandwidth. In this study, observations of the second-order NLHE in type-II Dirac semimetal CoTe2 under time-reversal symmetry are reported. This is determined by the disorder-induced extrinsic contribution on the broken-inversion-symmetry surface and room-temperature terahertz rectification without the need for semiconductor junctions or bias voltage. It is shown that remarkable photoresponsivity over 0.1 A W-1 , a response time of approximately 710 ns, and a mean noise equivalent power of 1 pW Hz-1/2 can be achieved at room temperature. The results open a new pathway for low-energy photon harvesting via nonlinear rectification induced by the NLHE in strongly spin-orbit-coupled and inversion-symmetry-breaking systems, promising a considerable impact in the field of infrared/terahertz photonics.

Investigation of Bacteria from Spoiled Bottled Salad Dressing Leading to Gas Explosion.

Background: In 2020, an incident involving spoiled salad dressing from a commercial source occurred. Upon opening the bottle, the contents exploded from gas that seemed to have fermented inside the bottle. For safety concerns, we sought to investigate the bacteria from the salad dressing in order to notify the company that made the product and relevant authorities. Methods: Anaerobic and carbon dioxide culture methods were used. To determine species of colonies, MALDI-TOF-MS and 16S rRNA whole sequencing were performed. Results: There were no colonies grown in anaerobic condition; however, we obtained three colonies from the carbon dioxide atmosphere. We determined the first colony as Alkalihalobacillus clausii (Bacillus clausii), the second as Bacillus spp. such as B. australimaris, B. safensis or B. safensis subsp. osmophilus and the third as B. paralicheniformis. Phylogenic tree analysis using the16S rRNA sequence revealed these colonies to be in a proximity of known gas-producing species. The NCBI database search revealed that a key gas production pathway gene, pyruvate formate-lyase (pfl), of which the gene product catalyzes pyruvate to formate conversion, exists in B. paralicheniformis. Formate dehydrogenase (FdhH) produces CO2 from formate that the coding gene fdhF positive bacteria can participate in gas production when formate is present in the culture. And we found fdhF from A. clausii, B. australimaris/B. safensis and B. paralicheniformis. Furthermore, under butanediol producing pathway, genes coding two enzymes involved in CO2 production, namely als and ald, existed in B. australimaris/B. safensis and B paralicheniformis, whereas A. clausii possessed als. Conclusion: Candidate species A. clausii, B. australimaris/B. safensis and B. paralicheniformis from spoiled salad dressing were thought to produce CO2 gas each from their own enzymes, or in combination, which caused the explosion upon opening. The endospore forming nature of Bacillus should alert us to be cautious when considering food producing process regulations where we need to thoroughly heat any product during manufacture in order to inactivate any bacteria as there is the possibility of this type of dangerous occurrence.

Influence of Orbital Character on the Ground State Electronic Properties in the van Der Waals Transition Metal Iodides VI3 and CrI3.

Two-dimensional van der Waals magnetic semiconductors display emergent chemical and physical properties and hold promise for novel optical, electronic and magnetic "few-layers" functionalities. Transition-metal iodides such as CrI3 and VI3 are relevant for future electronic and spintronic applications; however, detailed experimental information on their ground state electronic properties is lacking often due to their challenging chemical environment. By combining X-ray electron spectroscopies and first-principles calculations, we report a complete determination of CrI3 and VI3 electronic ground states. We show that the transition metal-induced orbital filling drives the stabilization of distinct electronic phases: a wide bandgap in CrI3 and a Mott insulating state in VI3. Comparison of surface-sensitive (angular-resolved photoemission spectroscopy) and bulk-sensitive (X-ray absorption spectroscopy) measurements in VI3 reveals a surface-only V2+ oxidation state, suggesting that ground state electronic properties are strongly influenced by dimensionality effects. Our results have direct implications in band engineering and layer-dependent properties of two-dimensional systems.

Disentangling Structural and Electronic Properties in V2O3 Thin Films: A Genuine Nonsymmetry Breaking Mott Transition.

Phase transitions are key in determining and controlling the quantum properties of correlated materials. Here, by using the combination of material synthesis and photoelectron spectroscopy, we demonstrate a genuine Mott transition undressed of any symmetry breaking side effects in the thin films of V2O3. In particular and in contrast with the bulk V2O3, we unveil the purely electronic dynamics approaching the metal-insulator transition, disentangled from the structural transformation that is prevented by the residual substrate-induced strain. On approaching the transition, the spectral signal evolves slowly over a wide temperature range, the Fermi wave-vector does not change, and the critical temperature is lower than the one reported for the bulk. Our findings are fundamental in demonstrating the universal benchmarks of a genuine nonsymmetry breaking Mott transition, extendable to a large array of correlated quantum systems, and hold promise of exploiting the metal-insulator transition by implementing V2O3 thin films in devices.

Evidence of a 2D Electron Gas in a Single-Unit-Cell of Anatase TiO2 (001).

The formation and the evolution of electronic metallic states localized at the surface, commonly termed 2D electron gas (2DEG), represents a peculiar phenomenon occurring at the surface and interface of many transition metal oxides (TMO). Among TMO, titanium dioxide (TiO2 ), particularly in its anatase polymorph, stands as a prototypical system for the development of novel applications related to renewable energy, devices and sensors, where understanding the carrier dynamics is of utmost importance. In this study, angle-resolved photo-electron spectroscopy (ARPES) and X-ray absorption spectroscopy (XAS) are used, supported by density functional theory (DFT), to follow the formation and the evolution of the 2DEG in TiO2 thin films. Unlike other TMO systems, it is revealed that, once the anatase fingerprint is present, the 2DEG in TiO2 is robust and stable down to a single-unit-cell, and that the electron filling of the 2DEG increases with thickness and eventually saturates. These results prove that no critical thickness triggers the occurrence of the 2DEG in anatase TiO2 and give insight in formation mechanism of electronic states at the surface of TMO.

Efficient Hydrogen Evolution Reaction with Bulk and Nanostructured Mitrofanovite Pt3Te4.

Here, we discuss the key features of electrocatalysis with mitrofanovite (Pt3Te4), a recently discovered mineral with superb performances in hydrogen evolution reaction. Mitrofanovite is a layered topological metal with spin-polarized topological surface states with potential applications for spintronics. However, mitrofanovite is also an exceptional platform for electrocatalysis, with costs of the electrodes suppressed by 47% owing to the partial replacement of Pt with Te. Remarkably, the Tafel slope in nanostructured mitrofanovite is just 33 mV/dec, while reduced mitrofanovite has the same Tafel slope (36 mV/dec) as state-of-the-art electrodes of pure Pt. Mitrofanovite also affords surface stability and robustness to CO poisoning. Accordingly, these findings pave the way for the advent of mitrofanovite for large-scale hydrogen production.

Stx2 Induces Differential Gene Expression and Disturbs Circadian Rhythm Genes in the Proximal Tubule.

Shiga toxin-producing Escherichia coli (STEC) causes proximal tubular defects in the kidney. However, factors altered by Shiga toxin (Stx) within the proximal tubules are yet to be shown. We determined Stx receptor Gb3 in murine and human kidneys and confirmed the receptor expression in the proximal tubules. Stx2-injected mouse kidney tissues and Stx2-treated human primary renal proximal tubular epithelial cell (RPTEC) were collected and microarray analysis was performed. We compared murine kidney and RPTEC arrays and selected common 58 genes that are differentially expressed vs. control (0 h, no toxin-treated). We found that the most highly expressed gene was GDF15, which may be involved in Stx2-induced weight loss. Genes associated with previously reported Stx2 activities such as src kinase Yes phosphorylation pathway activation, unfolded protein response (UPR) and ribotoxic stress response (RSR) showed differential expressions. Moreover, circadian clock genes were differentially expressed, suggesting Stx2-induced renal circadian rhythm disturbance. Circadian rhythm-regulated proximal tubular Na+-glucose transporter SGLT1 (SLC5A1) was down-regulated, indicating proximal tubular functional deterioration, and mice developed glucosuria confirming proximal tubular dysfunction. Stx2 alters gene expression in murine and human proximal tubules through known activities and newly investigated circadian rhythm disturbance, which may result in proximal tubular dysfunctions.

Evidence of magnetism-induced topological protection in the axion insulator candidate EuSn2P2.

We unravel the interplay of topological properties and the layered (anti)ferromagnetic ordering in EuSn2P2, using spin and chemical selective electron and X-ray spectroscopies supported by first-principle calculations. We reveal the presence of in-plane long-range ferromagnetic order triggering topological invariants and resulting in the multiple protection of topological Dirac states. We provide clear evidence that layer-dependent spin-momentum locking coexists with ferromagnetism in this material, a cohabitation that promotes EuSn2P2 as a prime candidate axion insulator for topological antiferromagnetic spintronics applications.

A machine learning model of microscopic agglutination test for diagnosis of leptospirosis.

Leptospirosis is a zoonosis caused by the pathogenic bacterium Leptospira. The Microscopic Agglutination Test (MAT) is widely used as the gold standard for diagnosis of leptospirosis. In this method, diluted patient serum is mixed with serotype-determined Leptospires, and the presence or absence of aggregation is determined under a dark-field microscope to calculate the antibody titer. Problems of the current MAT method are 1) a requirement of examining many specimens per sample, and 2) a need of distinguishing contaminants from true aggregates to accurately identify positivity. Therefore, increasing efficiency and accuracy are the key to refine MAT. It is possible to achieve efficiency and standardize accuracy at the same time by automating the decision-making process. In this study, we built an automatic identification algorithm of MAT using a machine learning method to determine agglutination within microscopic images. The machine learned the features from 316 positive and 230 negative MAT images created with sera of Leptospira-infected (positive) and non-infected (negative) hamsters, respectively. In addition to the acquired original images, wavelet-transformed images were also considered as features. We utilized a support vector machine (SVM) as a proposed decision method. We validated the trained SVMs with 210 positive and 154 negative images. When the features were obtained from original or wavelet-transformed images, all negative images were misjudged as positive, and the classification performance was very low with sensitivity of 1 and specificity of 0. In contrast, when the histograms of wavelet coefficients were used as features, the performance was greatly improved with sensitivity of 0.99 and specificity of 0.99. We confirmed that the current algorithm judges the positive or negative of agglutinations in MAT images and gives the further possibility of automatizing MAT procedure.

Mitrofanovite Pt3Te4: A Topological Metal with Termination-Dependent Surface Band Structure and Strong Spin Polarization.

Due to their peculiar quasiparticle excitations, topological metals have high potential for applications in the fields of spintronics, catalysis, and superconductivity. Here, by combining spin- and angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and density functional theory, we discover surface-termination-dependent topological electronic states in the recently discovered mitrofanovite Pt3Te4. Mitrofanovite crystal is formed by alternating, van der Waals bound layers of Pt2Te2 and PtTe2. Our results demonstrate that mitrofanovite is a topological metal with termination-dependent (i) electronic band structure and (ii) spin texture. Despite their distinct electronic character, both surface terminations are characterized by electronic states exhibiting strong spin polarization with a node at the Γ point and sign reversal across the Γ point, indicating their topological nature and the possibility of realizing two distinct electronic configurations (both of them with topological features) on the surface of the same material.