Strongly Coupled Magnon-Plasmon Polaritons in Graphene-Two-Dimensional Ferromagnet Heterostructures

Magnons and plasmons are different collective modes, involving the spin and charge degrees of freedom, respectively. Formation of hybrid plasmon-magnon polaritons in heterostructures of plasmonic and magnetic systems faces two challenges, the small interaction of the electromagnetic field of the plasmon with the spins, and the energy mismatch, as in most systems plasmons have energies orders of magnitude larger than those of magnons. We show that graphene plasmons form polaritons with the magnons of two-dimensional ferromagnetic insulators, placed up to to half a micrometer apart, with Rabi splittings in the range of 100 GHz (dramatically larger than cavity magnonics). This is facilitated both by the small energy of graphene plasmons and the cooperative super-radiant nature of the plasmon-magnon coupling afforded by phase matching. We show that the coupling can be modulated both electrically and mechanically, and we propose a ferromagnetic resonance experiment implemented with a two-dimensional ferromagnet driven by graphene plasmons.

Excitonic instability in transition metal dichalcogenides

When transition-metal dichalcogenide monolayers lack inversion symmetry, their low-energy single particle spectrum near some high-symmetry points can, in some cases, be described by tilted massive Dirac Hamiltonians. The so-called Janus materials fall into that category. Inversion symmetry can also be broken by the application of out-of-plane electric fields, or by the mere presence of a substrate. Here we explore the properties of excitons in TMDC monolayers lacking inversion symmetry. We find that exciton binding energies can be larger than the electronic band gap, making such materials promising candidates to host the elusive exciton insulator phase. We also investigate the excitonic contribution to their optical conductivity and discuss the associated optical selection rules.

Enhancing the hybridization of plasmons in graphene with 2D superconductor collective modes

We explore ways in which the close proximity between graphene sheets and monolayers of 2D superconductors can lead to hybridization between their collective excitations. We consider heterostructures formed by combinations of graphene sheets and 2D superconductor monolayers. The broad range of energies in which the graphene plasmon can exist, together with its tunability, makes such heterostructures promising platforms for probing the many-body physics of superconductors. We show that the hybridization between the graphene plasmon and the Bardasis-Schrieffer mode of a 2D superconductor results in clear signatures on the near-field reflection coefficient of the heterostructure, which in principle can be observed in scanning near-field microscopy experiments.

Harnessing ultraconfined graphene plasmons to probe the electrodynamics of superconductors

We show that the Higgs mode of a superconductor, which is usually challenging to observe by far-field optics, can be made clearly visible using near-field optics by harnessing ultraconfined graphene plasmons. As near-field sources we investigate two examples: graphene plasmons and quantum emitters. In both cases the coupling to the Higgs mode is clearly visible. In the case of the graphene plasmons, the coupling is signaled by a clear anticrossing stemming from the interaction of graphene plasmons with the Higgs mode of the superconductor. In the case of the quantum emitters, the Higgs mode is observable through the Purcell effect. When combining the superconductor, graphene, and the quantum emitters, a number of experimental knobs become available for unveiling and studying the electrodynamics of superconductors.

β-tungsten: a promising metal for spintronics

Ultrathin films of β-tungsten provide very promising substrates for applications in spintronics, and the possibility of incorporating them into multilayers extends such expectations. Our calculations indicate that it is viable to deposit a single layer of Mn on two non-equivalent (0 0 1) surfaces of β-tungsten that have easy axes along orthogonal directions [0 1 0] and [1 0 0], respectively. The ferromagnetic structure of this Mn monolayer adsorbed to either of those surfaces displays a giant in-plane magneto-crystalline anisotropy that exceeds 12 meV per Mn atom. Furthermore, when coated with additional layers of β-tungsten the magnetization easy axis becomes perpendicular to the planes. We envisage that magnetic multilayers involving mono-crystalline thin films of β-tungsten oriented along high-symmetry directions offer a very fruitful playground for spintronic applications.

Endophytic bacterial microbiome associated with leaves of genetically modified (AtAREB1) and conventional (BR 16) soybean plants

Plant leaves (phyllosphere) have a great potential for colonization and microbial growth, consisting of a dynamic environment in which several factors can interfere with the microbial population structure. The use of genetically modified (GM) plants has introduced several traits in agriculture, such as the improvement of plant drought tolerance, as observed in the AtAREB1 transcription factor overexpression in soybean (Glycine max L. Merrill). The present study aimed at investigating the taxonomic and functional profile of the leaf microbial community of bacteria found in GM (drought-tolerant event 1Ea2939) and conventional (BR 16) soybean plants. Bacterial DNA was extracted from leaf samples collected from each genotype and used for microbial diversity and richness analysis through the MiSeq Illumina platform. Functional prediction was performed using the PICRUSt tool and the STAMP v 2.1.3 software. The obtainment of the GM event 1Ea2939 showed minimum effects on the microbial community and in the potential for chemical-genetic communication, i.e. in the potential for symbiotic and/or mutualistic interaction between plants and their natural microbiota.

Bioprospection of Culturable Endophytic Fungi Associated with the Ornamental Plant Pachystachys lutea

Endophytes are fungi and bacteria that inhabit plant tissues without causing disease. Endophytes have characteristics that are important for the health of the plant and have been isolated from several plants of economic and medicinal interest but rarely from ornamental plants. The current study isolates and identifies endophytic fungi from the leaves of Pachystachys lutea and evaluates the antagonistic activity of these endophytes as well as cellulase production by the endophytes. Fungi were isolated by fragmentation from surface-disinfected leaves and were identified by the sequencing of the ITS gene and the genes coding for EF 1-α and β-tubulin followed by multilocus sequence analysis. Molecular taxonomic analysis revealed that 78% of the identified fungi belonged to the genus Diaporthe. We also identified strains belonging to the genera Colletotrichum, Phyllosticta, Xylaria, Nemania, and Alternaria. Most of the strains tested were able to inhibit the growth of pathogenic fungi, especially PL09 (Diaporthe sp.), which inhibited the growth of Colletotrichum sp., and PL03 (Diaporthe sp.), which inhibited the growth of Fusarium oxysporum. The production of cellulase ranged from 0.87 to 1.60 μmol/min. Foliar endophytic fungal isolates from P. lutea showed promising results for the in vitro control of plant pathogens and for cellulase production. This paper is the first report on culturable endophytic fungi isolated from the ornamental plant P. lutea.

Molecular phylogeny and biotechnological potential of bacterial endophytes associated with Malpighia emarginata

Acerola (Malpighia emarginata) is a shrub native to tropical and subtropical climates, which has great commercial interest due to the high vitamin C content of its fruit. However, there are no reports of the endophytic community of this plant species. The aim of this study was to verify the genetic diversity of the leaf endophytic bacterial community of two varieties (Olivier & Waldy Cati 30) of acerola, and to evaluate their biotechnological ability by assessing their in vitro control of pathogenic fungi and the enzymatic production of cellulase, xylanase, amylase, pectinase, protease, lipase, esterase, and chitinase. In total, 157 endophytic bacteria were isolated from the leaves of two varieties of the plant at 28° and 37°C. Phylogenetic analysis confirmed the molecular identification of 58 bacteria, 39.65% of which were identified at the species level. For the first time, the genus Aureimonas was highlighted as an endophytic bacterium. Furthermore, 12.82% of the isolates inhibited the growth of all phytopathogens evaluated and at least one of the above-mentioned enzymes was produced by 64.70% of the endophytes, demonstrating that M. emarginata isolates have potential use in biotechnological studies.

The receptor-like kinase SlSOBIR1 is differentially modulated by virus infection but its overexpression in tobacco has no significant impact on virus accumulation

KEY MESSAGE

The role of the tomato receptor-like kinase SlSOBIR1 in antiviral defense was investigated. SlSOBIR1 was transcriptionally modulated by unrelated viruses but its ectopic expression had no effect on virus accumulation. Leucine-rich repeat receptor-like kinases (LRR-RLK) constitute a diverse group of proteins allowing the cell to recognize and respond to the extracellular environment. In the present study we focused on a gene encoding a tomato LRR-RLK (named SlSOBIR1) involved in the host defense against fungal pathogens. Curiously, SlSOBIR1 has been previously reported to be down-regulated by Pepper yellow mosaic virus (PepYMV) infection. Here, we show that SlSOBIR1 is responsive to wounding and differentially modulated by unrelated virus infection, i.e., down-regulated by PepYMV and up-regulated by Tomato chlorotic spot virus (TCSV). Despite these divergent expression profiles, SlSOBIR1 overexpression in transgenic tobacco plants had no evident effect on TCSV and PepYMV accumulation. On the other hand, overexpression of SlSOBIR1 significantly increased the expression of selected defense genes (PR-1a and PR-6) and exacerbated superoxide production in wounded leaves. Our data indicate that the observed modulation of SlSOBIR1 expression is probably triggered by secondary effects of the virus infection process and suggest that SlSOBIR1 is not directly involved in antiviral signaling response.

Magnetic response of zigzag nanoribbons under electric fields

Spin excitations in zigzag graphene nanoribbons are studied when the system is subjected to an electric field in the transversal direction. The magnetic properties and the lifetime of the spin excitations are systematically investigated and compared using a tight-binding electron-electron model treated by a mean-field Hubbard model. The effects of electron-hole asymmetry introduced by next-nearest neighbor hopping are also investigated. We show that by increasing the electric field, the antiferromagnetic correlations between the edges of the nanoribbons are decreased due to a reduction of the magnetic moments. The results show that the spin wave lifetime may be controlled by the intensity of the transversal electric field, indicating that zigzag nanoribbons may be considered great candidates for future spintronic applications.

Graphene as a non-magnetic spin current lens

In spintronics, the ability to transport magnetic information often depends on the existence of a spin current traveling between two different magnetic objects acting as the source and probe. A large fraction of this information never reaches the probe and is lost because the spin current tends to travel omnidirectionally. We propose that a curved boundary between a gated and a non-gated region within graphene acts as an ideal lens for spin currents despite being entirely of non-magnetic nature. We show as a proof of concept that such lenses can be utilized to redirect the spin current that travels away from a source onto a focus region where a magnetic probe is located, saving a considerable fraction of the magnetic information that would be otherwise lost.

Itinerant nature of atom-magnetization excitation by tunneling electrons

We have performed single-atom magnetization curve (SAMC) measurements and inelastic scanning tunneling spectroscopy (ISTS) on individual Fe atoms on a Cu(111) surface. The SAMCs show a broad distribution of magnetic moments with 3.5 μB being the mean value. ISTS reveals a magnetization excitation with a lifetime of 200 fsec which decreases by a factor of 2 upon application of a magnetic field of 12 T. The experimental observations are quantitatively explained by the decay of the magnetization excitation into Stoner modes of the itinerant electron system as shown by newly developed theoretical modeling.

Dynamical magnetic excitations of nanostructures from first principles

Within time-dependent density functional theory, combined with the Korringa-Kohn-Rostoker Green functions, we devise a real space method to investigate spin dynamics. Our scheme enables one to deduce the Coulomb potential which assures a proper Goldstone mode is present. We illustrate with application to 3d adatoms and dimers on Cu(100).

Marginal adaptation and microleakage of five root-end filling materials: an in vitro study

AIM

Endodontic surgery consists of several procedures which involve the endodontic space or the root canal and is performed as an alternative to unsuccessful outcomes or complications following endodontic treatments. The aim of the study was to evaluate the sealing ability of five root-end filling materials.

METHODS

Fifty human single rooted teeth were treated endodontically; roots were resected at 3 mm from the apex, and root end cavities were prepared with ultrasonic tips. Root ends were filled with one of the following materials: silver amalgam (control group); mineral trioxide aggregate; white Portland cement; Vitremer; and Fuji Ortho. Apical sealing was evaluated by evaluating microleakage of 50% silver nitrate solution. The apical portion of the roots was sectioned to obtain 1-mm thick transversal slices, and epoxy resin replicas of these apical slices were produced. A scanning electron microscope (SEM) was used for analyses. The Kruskal-Wallis test and a multiple comparisons test were used for statistical data analysis.

RESULTS

Results showed microleakage and variable adaptation gaps on the interface between dentin and root-end filling material in all specimens.

CONCLUSION

All the studied materials exhibited some degree of apical microleakage and marginal gaps. No correlation was found between data obtained from analyses of apical sealing and marginal adaptation.

Entanglement of two impurities through electron scattering

We study how two magnetic impurities embedded in a solid can be entangled by an injected electron scattering between them and by subsequent measurement of the electron's state. We start by investigating an ideal case where only the electronic spin interacts successively through the same unitary operation with the spins of the two impurities. We find conditions for the impurity spins to be maximally entangled with a significant success probability. We then consider a more realistic description which includes both the forward and backscattering amplitudes. In this scenario, we obtain the entanglement between the impurities as a function of the interaction strength of the electron-impurity coupling. We find that our scheme allows us to entangle the impurities maximally with a significant probability.

Ground state of magnetic dimers on metal surfaces

We present model studies of the ground state for magnetic dimers on metal surfaces. We find it can be neither ferromagnetic nor antiferromagnetic, but is often canted for nearest neighbors. Thus, the system cannot be described using bilinear exchange. We give a criterion which can be used quite generally to interrogate the local stability of ferromagnetically or antiferromagnetically aligned dimers, and which also may be used to infer the canting angle when canted states are stable.

Impurity scattering induced entanglement of ballistic electrons

We show how entanglement between two conduction electrons is generated in the presence of a localized magnetic impurity embedded in an otherwise ballistic conductor of special geometry. This process is a generalization of beam-splitter mediated entanglement generation schemes with a localized spin placed at the site of the beam splitter. Our entangling scheme is unconditional and robust to randomness of the initial state of the impurity. The entangled state generated manifests itself in noise reduction of spin-dependent currents.