Above-Room-Temperature Ferromagnetism in Thin van der Waals Flakes of Cobalt-Substituted Fe5GeTe2.

Two-dimensional (2D) magnetic van der Waals materials provide a powerful platform for studying the fundamental physics of low-dimensional magnetism, engineering novel magnetic phases, and enabling thin and highly tunable spintronic devices. To realize high-quality and practical devices for such applications, there is a critical need for robust 2D magnets with ordering temperatures above room temperature that can be created via exfoliation. Here, the study of exfoliated flakes of cobalt-substituted Fe5GeTe2 (CFGT) exhibiting magnetism above room temperature is reported. Via quantum magnetic imaging with nitrogen-vacancy centers in diamond, ferromagnetism at room temperature was observed in CFGT flakes as thin as 16 nm corresponding to 16 layers. This result expands the portfolio of thin room-temperature 2D magnet flakes exfoliated from robust single crystals that reach a thickness regime relevant to practical spintronic applications. The Curie temperature Tc of CFGT ranges from 310 K in the thinnest flake studied to 328 K in the bulk. To investigate the prospect of high-temperature monolayer ferromagnetism, Monte Carlo calculations were performed, which predicted a high value of Tc of ∼270 K in CFGT monolayers. Pathways toward further enhancing monolayer Tc are discussed. These results support CFGT as a promising platform for realizing high-quality room-temperature 2D magnet devices.

In-depth genome analysis of Bacillus sp. BH32, a salt stress-tolerant endophyte obtained from a halophyte in a semiarid region.

Endophytic strains belonging to the Bacillus cereus group were isolated from the halophytes Atriplex halimus L. (Amaranthaceae) and Tamarix aphylla L. (Tamaricaceae) from costal and continental regions in Algeria. Based on their salt tolerance (up to 5%), the strains were tested for their ability to alleviate salt stress in tomato and wheat. Bacillus sp. strain BH32 showed the highest potential to reduce salinity stress (up to + 50% and + 58% of dry weight improvement, in tomato and wheat, respectively, compared to the control). To determine putative mechanisms involved in salt tolerance and plant growth promotion, the whole genome of Bacillus sp. BH32 was sequenced, annotated, and used for comparative genomics against the genomes of closely related strains. The pangenome of Bacillus sp. BH32 and its closest relative was further analyzed. The phylogenomic analyses confirmed its taxonomic position, a member of the Bacillus cereus group, with intergenomic distances (GBDP analysis) pinpointing to a new taxon (digital DNA-DNA hybridization, dDDH < 70%). Genome mining unveiled several genes involved in stress tolerance, production of anti-oxidants and genes involved in plant growth promotion as well as in the production of secondary metabolites. KEY POINTS : • Bacillus sp. BH32 and other bacterial endophytes were isolated from halophytes, to be tested on tomato and wheat and to limit salt stress adverse effects. • The strain with the highest potential was then studied at the genomic level to highlight numerous genes linked to plant growth promotion and stress tolerance. • Pangenome approaches suggest that the strain belongs to a new taxon within the Bacillus cereus group.

Quantum Spin Torque Driven Transmutation of an Antiferromagnetic Mott Insulator.

The standard model of spin-transfer torque (STT) in antiferromagnetic spintronics considers the exchange of angular momentum between quantum spins of flowing electrons and noncollinear-to-them localized spins treated as classical vectors. These vectors are assumed to realize Néel order in equilibrium, ↑↓⋯↑↓, and their STT-driven dynamics is described by the Landau-Lifshitz-Gilbert (LLG) equation. However, many experimentally employed materials (such as archetypal NiO) are strongly electron-correlated antiferromagnetic Mott insulators (AFMIs) whose localized spins form a ground state quite different from the unentangled Néel state |↑↓⋯↑↓⟩. The true ground state is entangled by quantum spin fluctuations, leading to the expectation value of all localized spins being zero, so that LLG dynamics of classical vectors of fixed length rotating due to STT cannot even be initiated. Instead, a fully quantum treatment of both conduction electrons and localized spins is necessary to capture the exchange of spin angular momentum between them, denoted as quantum STT. We use a recently developed time-dependent density matrix renormalization group approach to quantum STT to predict how injection of a spin-polarized current pulse into a normal metal layer coupled to an AFMI overlayer via exchange interaction and possibly small interlayer hopping-mimicking, e.g., topological-insulator/NiO bilayer employed experimentally-will induce a nonzero expectation value of AFMI localized spins. This new nonequilibrium phase is a spatially inhomogeneous ferromagnet with a zigzag profile of localized spins. The total spin absorbed by AFMI increases with electron-electron repulsion in AFMIs, as well as when the two layers do not exchange any charge.

Spintronics Meets Nonadiabatic Molecular Dynamics: Geometric Spin Torque and Damping on Dynamical Classical Magnetic Texture due to an Electronic Open Quantum System.

We analyze a quantum-classical hybrid system of steadily precessing around the fixed axis slow classical localized magnetic moments (LMMs), forming a head-to-head domain wall, surrounded by fast electrons driven out of equilibrium by LMMs and residing within a metallic wire whose connection to macroscopic reservoirs makes electronic quantum system an open one. The model captures the essence of dynamical noncollinear magnetic textures encountered in spintronics, while making it possible to obtain the exact time-dependent nonequilibrium density matrix of electronic systems and split it into four contributions. The Fermi surface contribution generates dissipative (or dampinglike in spintronics terminology) spin torque on LMMs, as the counterpart of electronic friction in nonadiabatic molecular dynamics (MD). Among two Fermi sea contributions, one generates geometric torque dominating in the adiabatic regime, which remains as the only nonzero contribution in a closed system with disconnected reservoirs. Locally geometric torque can have nondissipative (or fieldlike in spintronics terminology) component, acting as the counterpart of geometric magnetism force in nonadiabatic MD, as well as a much smaller dampinglike component acting as "geometric friction." Such current-independent geometric torque is absent from widely used micromagnetics or atomistic spin dynamics modeling of magnetization dynamics based on the Landau-Lifshitz-Gilbert equation, while previous analyses of how to include our Fermi-surface dampinglike torque have severely underestimated its total magnitude.

Proximity Spin-Orbit Torque on a Two-Dimensional Magnet within van der Waals Heterostructure: Current-Driven Antiferromagnet-to-Ferromagnet Reversible Nonequilibrium Phase Transition in Bilayer CrI3.

The recently discovered two-dimensional magnetic insulator CrI3 is an intriguing case for basic research and spintronic applications since it is a ferromagnet in the bulk but an antiferromagnet in bilayer form, with its magnetic ordering amenable to external manipulations. Using the first-principles quantum transport approach, we predict that injecting unpolarized charge current parallel to the interface of the bilayer-CrI3/monolayer-TaSe2 van der Waals (vdW) heterostructure will induce spin-orbit torque and thereby drive the dynamics of magnetization on the first monolayer of CrI3 in direct contact with TaSe2. By combining the calculated complex angular dependence of spin-orbit torque with the Landau-Lifshitz-Gilbert equation for classical dynamics of magnetization, we demonstrate that current pulses can switch the direction of magnetization on the first monolayer to become parallel to that of the second monolayer, thereby converting CrI3 from antiferromagnet to ferromagnet while not requiring any external magnetic field. We explain the mechanism of this reversible current-driven nonequilibrium phase transition by showing that first monolayer of CrI3 carries current due to evanescent wave functions injected by metallic transition metal dichalcogenide TaSe2, while concurrently acquiring strong spin-orbit coupling via such a proximity effect, whereas the second monolayer of CrI3 remains insulating. The transition can be detected by passing vertical read current through the vdW heterostructure, encapsulated by a bilayer of hexagonal boron nitride and sandwiched between graphite electrodes, where we find a tunneling magnetoresistance of ≃240%.

Proximity Band Structure and Spin Textures on Both Sides of Topological-Insulator/Ferromagnetic-Metal Interface and Their Charge Transport Probes.

The control of recently observed spintronic effects in topological-insulator/ferromagnetic-metal (TI/FM) heterostructures is thwarted by the lack of understanding of band structure and spin textures around their interfaces. Here we combine density functional theory with Green's function techniques to obtain the spectral function at any plane passing through atoms of Bi2Se3 and Co or Cu layers comprising the interface. Instead of naively assumed Dirac cone gapped by the proximity exchange field spectral function, we find that the Rashba ferromagnetic model describes the spectral function on the surface of Bi2Se3 in contact with Co near the Fermi level EF0, where circular and snowflake-like constant energy contours coexist around which spin locks to momentum. The remnant of the Dirac cone is hybridized with evanescent wave functions from metallic layers and pushed, due to charge transfer from Co or Cu layers, a few tenths of an electron-volt below EF0 for both Bi2Se3/Co and Bi2Se3/Cu interfaces while hosting distorted helical spin texture wounding around a single circle. These features explain recent observation of sensitivity of spin-to-charge conversion signal at TI/Cu interface to tuning of EF0. Crucially for spin-orbit torque in TI/FM heterostructures, few monolayers of Co adjacent to Bi2Se3 host spectral functions very different from the bulk metal, as well as in-plane spin textures (despite Co magnetization being out-of-plane) due to proximity spin-orbit coupling in Co induced by Bi2Se3. We predict that out-of-plane tunneling anisotropic magnetoresistance in Cu/Bi2Se3/Co vertical heterostructure can serve as a sensitive probe of the type of spin texture residing at EF0.

Secondary metabolite genes encoded by potato rhizosphere microbiomes in the Andean highlands are diverse and vary with sampling site and vegetation stage.

Potato (Solanum tuberosum) is an important staple crop worldwide, it has been cultivated in the Andean Altiplano under low-input farming practices at high altitudes and under harsh environment for centuries. We analyzed secondary metabolite (SM) gene diversity encoded in the potato rhizosphere microbiome during plant growth at three distinct sites located in the Andes at high altitudes by 454-pyrosequencing of non-ribosomal peptide and polyketide biosynthetic genes. Phylogenetic analysis indicated that the majority of rhizosphere SM-encoding sequences differed from previously known sequences and may have distinct ancestors. In particular, actinobacterial methyl-malonyl-CoA transferase and acyl carrier protein from Firmicutes, both involved in the synthesis of SMs, showed widespread distribution of clades which were clearly distinct from sequences deposited in public databases, and only 11% of these sequences could be linked to the production of specific classes of SMs. Although the same cultivar was analyzed, SM gene composition radically differed among plant growth stages and across sites, suggesting a distinct repertoire of SM genes that likely encode diverse SM structures. Also, great diversity of non-ribosomal peptide and polyketide biosynthetic pathways in potato-associated microbiomes in the Andean highlands may represent a rich source of novel natural products.

Surfactin variants mediate species-specific biofilm formation and root colonization in Bacillus.

Cyclic lipopeptides (cLP) and especially surfactins produced by Bacillus spp. trigger biofilm formation and root colonization and are crucial for biocontrol activity and systemic resistance in plants. Bacillus atrophaeus 176s isolated from the moss Tortella tortuosa produces the cLP fengycins, iturins and surfactins, possesses antifungal activities and can protect tomato, lettuce and sugar beet against Rhizoctonia solani infection. In B. atrophaeus we identified for the first time the variant surfactin C, which differs from surfactin A produced by B. subtilis and B. amyloliquefaciens by an isoleucine instead of a leucine at position 7 of the lipopeptide backbone. The analysis of the complete surfactin gene clusters revealed that the dissimilarity is encoded in the adenylation domain of srfC and show that surfactin variations are distributed in a species-specific manner in bacilli. We demonstrate that the surfactin A and C with subtle structural differences have varying signal strengths on biofilm formation and root colonization and act specifically on the respective producing strain. This became evident as biofilm formation and root colonization but not swarming motility in surfactin biosynthesis mutants was restored differentially in the presence of exogenously supplemented cognate and non-cognate surfactin variants.

The Draft Genome Sequence of Paenibacillus polymyxa Strain CCI-25 Encompasses High Potential for Secondary Metabolite Production.

We report here the draft genome sequence of Paenibacillus polymyxa strain CCI-25, which displays strong antifungal and antibacterial activities in vitro The genome encompasses nonribosomal peptide synthetases predicted to encode a tridecaptin, polymyxin, fusaricidin, an iturin-like synthetase, a lantibiotic similar to paenicidin A, as well as a type 1 polyketide synthase.

Nonperturbative Quantum Physics from Low-Order Perturbation Theory.

The Stark effect in hydrogen and the cubic anharmonic oscillator furnish examples of quantum systems where the perturbation results in a certain ionization probability by tunneling processes. Accordingly, the perturbed ground-state energy is shifted and broadened, thus acquiring an imaginary part which is considered to be a paradigm of nonperturbative behavior. Here we demonstrate how the low order coefficients of a divergent perturbation series can be used to obtain excellent approximations to both real and imaginary parts of the perturbed ground state eigenenergy. The key is to use analytic continuation functions with a built-in singularity structure within the complex plane of the coupling constant, which is tailored by means of Bender-Wu dispersion relations. In the examples discussed the analytic continuation functions are Gauss hypergeometric functions, which take as input fourth order perturbation theory and return excellent approximations to the complex perturbed eigenvalue. These functions are Borel consistent and dramatically outperform widely used Padé and Borel-Padé approaches, even for rather large values of the coupling constant.

Giant Spin Pumping and Inverse Spin Hall Effect in the Presence of Surface and Bulk Spin-Orbit Coupling of Topological Insulator Bi2Se3.

Three-dimensional (3D) topological insulators are known for their strong spin-orbit coupling (SOC) and the existence of spin-textured surface states that might be potentially exploited for "topological spintronics." Here, we use spin pumping and the inverse spin Hall effect to demonstrate successful spin injection at room temperature from a metallic ferromagnet (CoFeB) into the prototypical 3D topological insulator Bi2Se3. The spin pumping process, driven by the magnetization dynamics of the metallic ferromagnet, introduces a spin current into the topological insulator layer, resulting in a broadening of the ferromagnetic resonance (FMR) line width. Theoretical modeling of spin pumping through the surface of Bi2Se3, as well as of the measured angular dependence of spin-charge conversion signal, suggests that pumped spin current is first greatly enhanced by the surface SOC and then converted into a dc-voltage signal primarily by the inverse spin Hall effect due to SOC of the bulk of Bi2Se3. We find that the FMR line width broadens significantly (more than a factor of 5) and we deduce a spin Hall angle as large as 0.43 in the Bi2Se3 layer.

Giant thermoelectric effect in graphene-based topological insulators with heavy adatoms and nanopores.

Designing thermoelectric materials with high figure of merit ZT = S(2)GT/Ktot requires fulfilling three often irreconcilable conditions, that is, the high electrical conductance G, small thermal conductance Ktot, and high Seebeck coefficient S. Nanostructuring is one of the promising ways to achieve this goal as it can substantially suppress lattice contribution to Ktot. However, it may also unfavorably influence the electronic transport in an uncontrollable way. Here, we theoretically demonstrate that this issue can be ideally solved by fabricating graphene nanoribbons with heavy adatoms and nanopores. The adatoms locally enhance spin-orbit coupling in graphene thereby converting it into a two-dimensional topological insulator with a band gap in the bulk and robust helical edge states, which carry electrical current and generate a highly optimized power factor S(2)G per helical conducting channel due to narrow boxcar-function-shaped electronic transmission (surpassing even the Mahan-Sofo limit obtained for delta-function-shaped electronic transmission). Concurrently, the array of nanopores impedes the lattice thermal conduction through the bulk. Using quantum transport simulations coupled with first-principles electronic and phononic band structure calculations, the thermoelectric figure of merit is found to reach its maximum ZT ≃ 3 at low temperatures T ≃ 40 K. This paves a way to design high-ZT materials by exploiting the nontrivial topology of electronic states through nanostructuring.

Spin-orbit coupling induced spin-transfer torque and current polarization in topological-insulator/ferromagnet vertical heterostructures.

We predict an unconventional spin-transfer torque (STT) acting on the magnetization of a free ferromagnetic (F) layer within N/TI/F vertical heterostructures, which originates from strong spin-orbit coupling on the surface of a three-dimensional topological insulator (TI), as well as from charge current becoming spin polarized in the direction of transport as it flows perpendicularly from the normal metal (N) across the bulk of the TI layer. The STT vector has both in-plane and perpendicular components that are comparable in magnitude to conventional torque in F'/I/F (where I stands for insulator) magnetic tunnel junctions, while not requiring additional spin-polarizing F' layer with fixed magnetization, which makes it advantageous for spintronics applications. Our principal formal result is a derivation of the nonequilibrium Green function-based formula and the corresponding gauge-invariant nonequilibrium density matrix, which makes it possible to analyze the components of the STT vector in the presence of arbitrary strong spin-orbit coupling either in the bulk or at the interface of the free F layer.

DNA base-specific modulation of microampere transverse edge currents through a metallic graphene nanoribbon with a nanopore.

We study two-terminal devices for DNA sequencing that consist of a metallic graphene nanoribbon with zigzag edges (ZGNR) and a nanopore in its interior through which the DNA molecule is translocated. Using the nonequilibrium Green functions combined with density functional theory, we demonstrate that each of the four DNA nucleobases inserted into the nanopore, whose edge carbon atoms are passivated by either hydrogen or nitrogen, will lead to a unique change in the device conductance. Unlike other recent biosensors based on transverse electronic transport through translocated DNA, which utilize small (of the order of pA) tunneling current across a nanogap or a nanopore yielding a poor signal-to-noise ratio, our device concept relies on the fact that in ZGNRs local current density is peaked around the edges so that drilling a nanopore away from the edges will not diminish the conductance. Inserting a nucleobase into the nanopore affects the charge density in the surrounding area, thereby modulating edge conduction currents whose magnitude is of the order of microampere at bias voltage 0.1 V. The proposed biosensors are not limited to ZGNRs and they could be realized with other nanowires supporting transverse edge currents, such as chiral GNRs or wires made of two-dimensional topological insulators.

Metagenomic analysis of the 1-aminocyclopropane-1-carboxylate deaminase gene (acdS) operon of an uncultured bacterial endophyte colonizing Solanum tuberosum L.

Deamination of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is a key plant-beneficial trait found in many plant growth-promoting bacteria. In this study, we analysed ACC deaminase genes (acdS) of bacterial endophytes colonizing field-grown potato plants. PCR analysis revealed the presence of two types of acdS genes, the dominant one showing high homology to an acdS gene derived from Pseudomonas fluorescens. Construction, functional screening and sequence analysis of metagenomic libraries revealed clones containing the acdS gene identified in the PCR library. Sequence analysis of one metagenomic clone identified the entire acdS operon of an uncultivated endophyte and revealed that the acdS gene is coupled upstream with an acdR transcriptional regulator gene as previously found in P. putida strain UW4 (Grichko and Glick 2000). However, in-silico analysis of 195 fully sequenced, acdS-containing bacterial genomes revealed that the majority of strains, including numerous strains belonging to the genus Pseudomonas, do not contain an acdR regulatory gene in the vicinity of the acdS gene or elsewhere in the genome. The acdR (+)-acdS (+) operon was exclusively found in several Alpha- and Betaproteobacteria most prominently in the genus Burkholderia.

The effect of the addition of colloidal iridium oxide into sol-gel obtained titanium and ruthenium oxide coatings on titanium on their electrochemical properties.

Electrochemical properties of sol-gel processed Ti(0.6)Ir(0.4)O(2) and Ti(0.6)Ru(0.3)Ir(0.1)O(2) coatings on titanium substrate were investigated using cyclic voltammetry, polarization measurements and electrochemical impedance spectroscopy and compared to the properties of Ti(0.6)Ru(0.4)O(2) coating. The role of iridium oxide in the improvement of the electrocatalytic, capacitive and stability properties of titanium anodes activated by a RuO(2)-TiO(2) coating is discussed. The oxide sols were prepared by forced hydrolysis of the metal chlorides. The characterization by dynamic light scattering and X-ray diffraction showed that polydisperse oxide sols were obtained with the particles tending to form agglomerates. The presence of IrO(2) causes a suppression of the X-ray diffraction peaks of TiO(2) and RuO(2) in the sol-gel prepared Ti(0.6)Ir(0.4)O(2) and Ti(0.6)Ru(0.3)Ir(0.1)O(2) coatings. The IrO(2)-containing coatings had an enhanced charge storage ability and activity for the oxygen evolution reaction (OER) in comparison to Ti(0.6)Ru(0.4)O(2) coating. The voltammogram of the Ti(0.6)Ir(0.4)O(2)/Ti electrode showed well-resolved peaks related to Ir redox transitions, which are responsible for the enhanced charge storage ability of IrO(2)-containing coatings. Redox transitions of Ir were also registered in the high-frequency domain of the ac impedance spectra of the coatings as a semicircle with characteristics insensitive to the electrolyte composition and to the electrode potential prior to OER. However, the semicircle characteristics were different for the two IrO(2)-containing coatings, as well as at potentials outside the OER in comparison to those at which the OER occurs.

Quantum-interference-controlled three-terminal molecular transistors based on a single ring-shaped molecule connected to graphene nanoribbon electrodes.

We study molecular transistors where graphene nanoribbons act as three metallic electrodes connected to a ring-shaped 18-annulene molecule. Using the nonequilibrium Green function formalism combined with density functional theory, recently extended to multiterminal devices, we show that these nanostructures exhibit exponentially small transmission when the source and drain electrodes are attached in a configuration with destructive interference of electron paths around the ring. The third electrode, functioning either as an attached infinite-impedance voltage probe or as an "air-bridge" top gate covering half of molecular ring, introduces dephasing that brings the transistor into the "on" state with its transmission in the latter case approaching the maximum limit for a single conducting channel device. The current through the latter device can also be controlled in the far-from-equilibrium regime by applying a gate voltage.

Plectin 1f scaffolding at the sarcolemma of dystrophic (mdx) muscle fibers through multiple interactions with beta-dystroglycan.

In skeletal muscle, the cytolinker plectin is prominently expressed at Z-disks and the sarcolemma. Alternative splicing of plectin transcripts gives rise to more than eight protein isoforms differing only in small N-terminal sequences (5-180 residues), four of which (plectins 1, 1b, 1d, and 1f) are found at substantial levels in muscle tissue. Using plectin isoform-specific antibodies and isoform expression constructs, we show the differential regulation of plectin isoforms during myotube differentiation and their localization to different compartments of muscle fibers, identifying plectins 1 and 1f as sarcolemma-associated isoforms, whereas plectin 1d localizes exclusively to Z-disks. Coimmunoprecipitation and in vitro binding assays using recombinant protein fragments revealed the direct binding of plectin to dystrophin (utrophin) and beta-dystroglycan, the key components of the dystrophin-glycoprotein complex. We propose a model in which plectin acts as a universal mediator of desmin intermediate filament anchorage at the sarcolemma and Z-disks. It also explains the plectin phenotype observed in dystrophic skeletal muscle of mdx mice and Duchenne muscular dystrophy patients.

Nonequilibrium spin Hall accumulation in ballistic semiconductor nanostructures.

We demonstrate that the flow of a longitudinal unpolarized current through a ballistic two-dimensional electron gas with Rashba spin-orbit coupling will induce a nonequilibrium spin accumulation which has opposite signs for the two lateral edges and is, therefore, the principal observable signature of the spin Hall effect in two-probe semiconductor nanostructures. The magnitude of its out-of-plane component is gradually diminished by static disorder, while it can be enhanced by an in-plane transverse magnetic field. Moreover, our prediction of the longitudinal component of the spin Hall accumulation, which is insensitive to the reversal of the bias voltage, offers direct evidence to differentiate experimentally between the extrinsic, intrinsic, and mesoscopic spin Hall mechanisms.

Spin Hall current driven by quantum interferences in mesoscopic Rashba rings.

We propose an all-electrical nanostructure where pure spin current is induced in the transverse voltage probes attached to a quantum-coherent ballistic one-dimensional ring when unpolarized charge current is injected through its longitudinal leads. Tuning of the Rashba spin-orbit coupling in a semiconductor heterostructure hosting the ring generates quasiperiodic oscillations of the predicted spin-Hall current due to spin-sensitive quantum-interference effects caused by the difference in the Aharonov-Casher phase accumulated by opposite spin states. Its amplitude is comparable to that of the spin-Hall current predicted for finite-size (simply connected) two-dimensional electron gases, while it gets reduced gradually in wide two-dimensional rings or due to spin-independent disorder.