Noncollinear Ground State from a Four-Spin Chiral Exchange in a Tetrahedral Magnet.

We propose a quartic chiral term m_{x}m_{y}m_{z}∇·m for the energy density of a cubic ferromagnet with broken parity symmetry (point group T_{d}). We demonstrate that this interaction causes a phase transition from a collinear ferromagnetic state to a noncollinear magnetic cone ground state provided its strength exceeds the geometric mean of magnetic exchange and cubic anisotropy. The corresponding noncollinear ground state may also be additionally stabilized by an external magnetic field pointing along certain crystallographic directions. The four-spin chiral exchange does also manifest itself in peculiar magnon spectra and favors spin waves with the wave vector that is perpendicular to the average magnetization direction.

Publisher's Note: Anomalous Hall Effect in a 2D Rashba Ferromagnet [Phys. Rev. Lett. 117, 046601 (2016)].

This corrects the article DOI: 10.1103/PhysRevLett.117.046601.

Asymmetric and Symmetric Exchange in a Generalized 2D Rashba Ferromagnet.

Dzyaloshinskii-Moriya interaction (DMI) is investigated in a 2D ferromagnet (FM) with spin-orbit interaction of Rashba type at finite temperatures. The FM is described in the continuum limit by an effective s-d model with arbitrary dependence of spin-orbit coupling (SOC) and kinetic energy of itinerant electrons on the absolute value of momentum. In the limit of weak SOC, we derive a general expression for the DMI constant D from a microscopic analysis of the electronic grand potential. We compare D with the exchange stiffness A and show that, to the leading order in small SOC strength α_{R}, the conventional relation D=(4mα_{R}/ℏ)A, in general, does not hold beyond the Bychkov-Rashba model. Moreover, in this model, both A and D vanish at zero temperature in the metal regime (i.e., when two spin sub-bands are partly occupied). For nonparabolic bands or nonlinear Rashba coupling, these coefficients are finite and acquire a nontrivial dependence on the chemical potential that demonstrates the possibility to control the size and chirality of magnetic textures by adjusting a gate voltage.

Anomalous Hall Effect in a 2D Rashba Ferromagnet.

Skew scattering on rare impurity configurations is shown to dominate the anomalous Hall effect in a 2D Rashba ferromagnet. The mechanism originates in scattering on rare impurity pairs separated by distances of the order of the Fermi wavelength. The corresponding theoretical description goes beyond the conventional noncrossing approximation. The mechanism provides the only contribution to the anomalous Hall conductivity in the most relevant metallic regime and strongly modifies previously obtained results for lower energies in the leading order with respect to impurity strength.

Lévy Flights due to Anisotropic Disorder in Graphene.

We study transport properties of graphene with anisotropically distributed on-site impurities (adatoms) that are randomly placed on every third line drawn along carbon bonds. We show that stripe states characterized by strongly suppressed backscattering are formed in this model in the direction of the lines. The system reveals Lévy-flight transport in the stripe direction such that the corresponding conductivity increases as the square root of the system length. Thus, adding this type of disorder to clean graphene near the Dirac point strongly enhances the conductivity, which is in stark contrast with a fully random distribution of on-site impurities, which leads to Anderson localization. The effect is demonstrated both by numerical simulations using the Kwant code and by an analytical theory based on the self-consistent T-matrix approximation.

Magnetoresistance in two-component systems.

Two-component systems with equal concentrations of electrons and holes exhibit nonsaturating, linear magnetoresistance in classically strong magnetic fields. The effect is predicted to occur in finite-size samples at charge neutrality due to recombination. The phenomenon originates in the excess quasiparticle density developing near the edges of the sample due to the compensated Hall effect. The size of the boundary region is of the order of the electron-hole recombination length that is inversely proportional to the magnetic field. In narrow samples and at strong enough magnetic fields, the boundary region dominates over the bulk leading to linear magnetoresistance. Our results are relevant for two-and three-dimensional semimetals and narrow band semiconductors including most of the topological insulators.

Metal-insulator transition in graphene on boron nitride.

Electrons in graphene aligned with hexagonal boron nitride are modeled by Dirac fermions in a correlated random-mass landscape subject to a scalar- and vector-potential disorder. We find that the system is insulating in the commensurate phase since the average mass deviates from zero. At the transition the mean mass is vanishing and electronic conduction in a finite sample can be described by a critical percolation along zero-mass lines. In this case graphene at the Dirac point is in a critical state with the conductivity sqrt[3]e(2)/h. In the incommensurate phase the system behaves as a symplectic metal.

Quantum Hall criticality and localization in graphene with short-range impurities at the Dirac point.

We explore the longitudinal conductivity of graphene at the Dirac point in a strong magnetic field with two types of short-range scatterers: adatoms that mix the valleys and "scalar" impurities that do not mix them. A scattering theory for the Dirac equation is employed to express the conductance of a graphene sample as a function of impurity coordinates; an averaging over impurity positions is then performed numerically. The conductivity σ is equal to the ballistic value 4e2/πh for each disorder realization, provided the number of flux quanta considerably exceeds the number of impurities. For weaker fields, the conductivity in the presence of scalar impurities scales to the quantum-Hall critical point with σ≃4×0.4e2/h at half filling or to zero away from half filling due to the onset of Anderson localization. For adatoms, the localization behavior is also obtained at half filling due to splitting of the critical energy by intervalley scattering. Our results reveal a complex scaling flow governed by fixed points of different symmetry classes: remarkably, all key manifestations of Anderson localization and criticality in two dimensions are observed numerically in a single setup.

Coulomb drag in graphene near the Dirac point.

We study Coulomb drag in graphene near the Dirac point, focusing on the regime of interaction-dominated transport. We establish a novel, graphene-specific mechanism of Coulomb drag based on fast interlayer thermalization, inaccessible by standard perturbative approaches. Using the quantum kinetic equation framework, we derive a hydrodynamic description of transport in double-layer graphene in terms of electric and energy currents. In the clean limit the drag becomes temperature independent. In the presence of disorder the drag coefficient at the Dirac point remains nonzero due to higher-order scattering processes and interlayer disorder correlations. At low temperatures (diffusive regime) these contributions manifest themselves in the peak in the drag coefficient centered at the neutrality point with a magnitude that grows with lowering temperature.

Giant magnetodrag in graphene at charge neutrality.

We report experimental data and theoretical analysis of Coulomb drag between two closely positioned graphene monolayers in a weak magnetic field. Close enough to the neutrality point, the coexistence of electrons and holes in each layer leads to a dramatic increase of the drag resistivity. Away from charge neutrality, we observe nonzero Hall drag. The observed phenomena are explained by decoupling of electric and quasiparticle currents which are orthogonal at charge neutrality. The sign of magnetodrag depends on the energy relaxation rate and geometry of the sample.

[Synthesis and investigation of effects of conopressin S analogues on ion and water excretion by rat kidney].

The investigation deals with effect of analogues of conopressin S--a peptide of the vasopressin family with amino acid replacement in the 2nd and 4th positions (characteristic of invertebrate peptides)--on transport of water and ions in the rat kidney. At administration to female Wistar rats, 1-deamino-conopressin S produced a weak action on water transport and had no effect on urinary K+ and Na+ excretion. Its analogue, 1-deamino-Tyr2-conopressin S, caused antidiuretic and kaliuretic action without affecting the Na+ excretion. Estimation of significance of the variant of optic isomer of arginine in the 4th and 8th position of the molecular for the antidiuretic and kaliuretic action of the peptide showed that 1-deamino-Tyr2,D-Arg4-conopressin S and 1-deamino-Tyr2,D-Arg4,8-conopressin S did not affect the urinary K+ excretion and renal water reabsorption, whereas action of 1-deamino-Tyr2,D-Arg8-conopressin S did not differ from action of 1-deamino-Tyr2-conopressin S. Thus, it has been established that the selective kaliuretic action of analogues of conopressin S on rat kidney depends on the presence of tyrosine in the 2nd and of L-arginine, but not of D-arginine, in the 4th position of the molecule.

Color-dependent conductance of graphene with adatoms.

We study ballistic transport properties of graphene with a low concentration of vacancies or adatoms. The conductance of graphene doped to the Dirac point is found to depend on the relative distribution of impurities among different sites of the honeycomb lattice labeled in general by six colors. The conductivity is shown to be sensitive to the crystal orientation if adatom sites have a preferred color. Our theory is confirmed by numerical simulations using recursive Green's functions with no adjustable parameters.

Diffusion and criticality in undoped graphene with resonant scatterers.

A general theory is developed to describe graphene with an arbitrary number of isolated impurities. The theory provides a basis for an efficient numerical analysis of the charge transport and is applied to calculate the Dirac-point conductivity σ of graphene with resonant scatterers. In the case of smooth resonant impurities the symmetry class is identified as DIII and σ grows logarithmically with increasing impurity concentration. For vacancies (or strong on-site potential impurities, class BDI) σ saturates at a constant value that depends on the vacancy distribution among two sublattices.

Charge transport in graphene with resonant scatterers.

The full counting statistics for the charge transport through an undoped graphene sheet in the presence of strong potential impurities is studied. Treating the scattering off the impurity in the s-wave approximation, we calculate the impurity correction to the cumulant generating function. This correction is universal provided the impurity strength is tuned to a resonant value. In particular, the conductance of the sample acquires a correction of 16e{2}/(pi{2}h) per resonant impurity.

[Influence of new neurohypophyseal hormone analogs on sodium and water reabsorption in rat kidney].

New analogs of some neurohypophyseal hormones (oxypressin, hydrin, glumitocin, vasotocin) have been synthesized. Experiments with injection of these peptides to rats showed that substitution of C-terminal glycinamide on beta-ethanolamine (glycinol) or ethylamine in 1-deamino-arginine vasotocin resulted in loss of natriuretic but not antidiuretic activity. Analogs of oxypressin and hydrin exhibited neither natriuretic activity nor ability to affect water reabsorption. Glumitocin analog induced renal sodium ion excretion and did not influence potassium ion excretion.

Synthesis and antiviral activity of PB1 component of the influenza A RNA polymerase peptide fragments.

This study is devoted to the antiviral activity of peptide fragments from the PB1 protein - a component of the influenza A RNA polymerase. The antiviral activity of the peptides synthesized was studied in MDCK cell cultures against the pandemic influenza strain A/California/07/2009 (H1N1) pdm09. We found that peptide fragments 6-13, 6-14, 26-30, 395-400, and 531-540 of the PB1 protein were capable of suppressing viral replication in cell culture. Terminal modifications i.e. N-acetylation and C-amidation increased the antiviral properties of the peptides significantly. Peptide PB1 (6-14) with both termini modified showed maximum antiviral activity, its inhibitory activity manifesting itself during the early stages of viral replication. It was also shown that the fluorescent-labeled analog of this peptide was able to penetrate into the cell. The broad range of virus-inhibiting activity of PB1 (6-14) peptide was confirmed using a panel of influenza A viruses of H1, H3 and H5 subtypes including those resistant to oseltamivir, the leading drug in anti-influenza therapy. Thus, short peptide fragments of the PB1 protein could serve as leads for future development of influenza prevention and/or treatment agents.

Effects of opioid peptides and naloxone on nervous tissue in culture.

It was shown that opioid peptides stimulate nervous tissue growth in culture in the rat, which manifests itself in augmented outgrowth of neurites from explants and in an increase in the number of glial and fibroblast-like cells in the growth zone. The effects of opioid peptides ([Leu]- and [Met]-enkephalins, beta- and gamma-endorphins and some synthetic analogues of [Leu]-enkephalin) on the growth of organotypic cultures of rat sympathetic and dorsal root ganglia and spinal cord were investigated. Neurite outgrowth, cell composition, and size of the growth zone as well as the dynamics of its formation were estimated. Changes in the survival of neurons in dorsal root ganglion cultures were determined. The experiments were performed with living cultures as well as with fixed preparations. In experiments with sympathetic ganglia, it was demonstrated that a significant growth-promoting effect is exerted by peptides taken at concentrations of 10(-8) M to 10(-14) M. Naloxone does not eliminate the effects of peptides, but stimulates the growth at 10(-5) M to 10(-7) M. Studies with spinal cord revealed that naloxone (10(-6) M) enhances the response to [Leu]-enkephalin (10(-9) M). The survival of dorsal root ganglion neurons under the influence of a [leu]-enkephalin analog (10(-9) M) exceeds control values by approximately two to four times. Thus, opioid peptides were shown to exert a strong growth-promoting effect on nervous tissue in culture. This effect is dual: in neurons the peptides stimulate the outgrowth of neurites and their survival, while in glial cells they change the rate of their migration and, probably, their proliferation. It is suggested that opioid peptides, besides their already established functions, may play a role in the development and regeneration of nervous tissue.

Monoclonal antibodies to dalargin--a synthetic analog of enkephalins.

Monoclonal antibodies (MABs) to a new drug Dalargin (Tyr-D-Ala-Gly-Phe-Leu-Arg) enhancing ulcer healing have been produced. Dalargin is a synthetic analog of Leu-enkephalin. With about 40 compounds tested in competition radioimmunoassay it has been shown that specificity of the MABs is directed against the N-terminal tetrapeptide of the molecule. The MABs are sensitive to amino acid substitutions in any of the positions of the fragment and have no cross-reactivity with endogenous opioids. Their further application in pharmacokinetic studies in humans and for characterization of opioid receptors is discussed.

Signature of wave localization in the time dependence of a reflected pulse

The average power spectrum of a pulse reflected by a disordered medium embedded in an N-mode waveguide decays in time with a power law t(-p). We show that the exponent p increases from 3 / 2 to 2 after N2 scattering times, due to the onset of localization. We compare two methods to arrive at this result. The first method involves the analytic continuation to an imaginary absorption rate of a static scattering problem. The second method involves the solution of a Fokker-Planck equation for the frequency dependent reflection matrix, by means of a mapping onto a problem in non-Hermitian quantum mechanics.

Met-enkephalin-induced release into the blood of a factor causing postural asymmetry.

Met- and Leu-enkephalin applied subarachnoidally into the rostral portion of a transected spinal cord (at the T6-T7 level) induce postural asymmetry of the hind limbs in rats, Met-enkephalin being predominantly responsible for the flexion of the right, and Leu-enkephalin of the left, hind leg. The blood serum of rats injected with Met-enkephalin contains a factor which, when administered subarachnoidally into the caudal portion of the transected spinal cord, is capable of inducing the hind limb postural asymmetry--predominantly, with the right leg flexion. This factor is inactivated by papain and differs from Met- and Leu-enkephalin in chromatographic properties. Apparently, Met-enkephalin induces the release of a peptide factor into the blood, from the brain or organs innervated by the neurons lying above the cut. It is then carried with the blood to the hind limbs and effects the hind limb postural asymmetry.