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.

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.

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.

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.

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.

[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.

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.

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.

[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.

Electrostatic confinement of electrons in an integrable graphene quantum dot.

We compare the conductance of an undoped graphene sheet with a small region subject to an electrostatic gate potential for the cases that the dynamics in the gated region is regular (disc-shaped region) and classically chaotic (stadium). For the disc, we find sharp resonances that narrow upon reducing the area fraction of the gated region. We relate this observation to the existence of confined electronic states. For the stadium, the conductance loses its dependence on the gate voltage upon reducing the area fraction of the gated region, which signals the lack of confinement of Dirac quasiparticles in a gated region with chaotic classical electron dynamics.

[Selective effect of vasotocin analogues with amino acid substitutions in 4, 7, 8 positions on the water and cations excretion by the rat kidney].

Analogues ofarginine vasotocin with replacement of amino acids in 4, 7 and 8 positions of the hormone were synthesized. After water loading the injection of 1 x 10(-12) mol per 100 g BW 1-deamino-8-homoarginine vasotocin, 1-deamino-4-threonine-8-arginine vasotocin and 1-deamino-4-threonine-8-D-arginine vasotocin increased solute-free water reabsorption, but did not affect cations excretion (Na, K, Ca, Mg). Presence of glycine in 9th position and proline in 7th position ofa vasotocin molecule is essential for hormone interaction with a V2-receptor. In rats, injection of 5 x 10(-11) mol 1-deamino-8-homoarginine vasotocin or 1-deamino-4-threonine-8-arginine vasotocin dramatically increased urinary sodium and potassium excretion and enforced osmotically free water reabsorption but very little affected urinary magnesium and calcium excretion. The injection in the same dose of other synthesized vasotocin analogues did not affect the cations excretion. The issue of physiological mechanisms of kidney's selective response related to water, one- and bivalent cations excretion after injection of vasotocin analogues is discussed. Inhibition of cations transport is associated with activation of any V-receptor (but not V2-receptor). This effect takes place only in presence of L-arginine instead of D-arginine in the analogue.