Showing papers in "Jetp Letters in 2010"

Comments on the Paper "Detection of the Absorption Spectra of Water Clusters under Atmospheric Conditions" by V. I. Serdyukov, L. N. Sinitsa, and Yu. A. Poplavskii, Pis'ma Zh. Eksp. Teor. Fiz. 89, 12 (2009) (JETP Lett. 89, 10 (2009))

Abstract: A numerical simulation has been performed, indicating that the statement on the detection of water dimer absorption by V.I. Serdyukov et al. in Pis’ma Zh. Eksp. Teor. Fiz. 89, 12 (2009) [JETP Lett. 89, 10 (2009)] had been premature. Most of the revealed induced absorption can be attributed to water monomers.

Behavior of aluminum near an ultimate theoretical strength in experiments with femtosecond laser pulses

Abstract: The dynamics of the motion of the free surface of micron and submicron films under the action of a compression pulse excited in the process of femtosecond laser heating of the surface layer of a target has been investigated by femtosecond interferometric microscopy. The relation between the velocity of the shock wave and the particle velocity behind its front indicates the shock compression to 9–13 GPa is elastic in this duration range. This is also confirmed by the small (≤1 ps) time of an increase in the parameters in the shock wave. Shear stresses reached in this process are close to their estimated ultimate values for aluminum. The spall strength determined at a strain rate of 109 s−1 and a spall thickness of 250–300 nm is larger than half the ultimate strength of aluminum.

Acceleration of particles by nonrotating charged black holes

Abstract: Recently, in the series of works a new effect of acceleration of particles by black holes has been found. Under certain conditions, the energy in the center-of-mass system can become infinitely large. The essential ingredient of such effect is the rotation of a black hole. In this work, it has been argued that the similar effect exists for a nonrotating but charged black hole even for the simplest case of radial motion of particles in the Reissner-Nordstrom background. All main features of the effect under discussion due to rotating black holes have their counterpart for the nonrotating charged ones.

Superconducting triplet spin valve

Abstract: We study the critical temperature T c of SFF trilayers (S is a singlet superconductor, F is a ferromagnetic metal), where the long-range triplet superconducting component is generated at noncollinear magnetizations of the F layers. We demonstrate that T c can be a nonmonotonic function of the angle α between the magnetizations of the two F layers. The minimum is achieved at an intermediate α, lying between the parallel (P, α = 0) and antiparallel (AP, α = π) cases. This implies a possibility of a “triplet” spin-valve effect: at temperatures above the minimum T Tr but below T P and T AP , the system is superconducting only in the vicinity of the collinear orientations. At certain parameters, we predict a reentrant T c (α) behavior. At the same time, considering only the P and AP orientations, we find that both the “standard” (T P < T AP ) and “inverse” (T P > T AP ) switching effects are possible depending on parameters of the system.

Grain Boundary Layers in Nanocrystalline Ferromagnetic Zinc Oxide

Abstract: The complete solubility of an impurity in a polycrystal increases with decreasing grain size, because the impurity dissolves not only in the crystallite bulk but also on the grain boundaries. This effect is especially strong when the adsorption layers (or the grain boundary phases) are multilayer. For example, the Mn solubility in the nanocrystalline films (where the size of grains is ∼20 nm) is more than three times greater than that in the ZnO single crystals. The thin nanocrystalline Mn-doped ZnO films in the Mn concentration range 0.1–47 at % have been obtained from organic precursors (butanoates) by the “liquid ceramic” method. They have ferromagnetic properties, because the specific area of the grain boundaries in them is greater than the critical value [B.B. Straumal et al., Phys. Rev. B 79, 205206 (2009)]. The high-resolution electron transmission microscopy studies show that the ZnO nanocrystalline grains with the wurtzite lattice are separated by amorphous layers whose thickness increases with the Mn concentration. The morphology of these layers differs greatly from the structure of the amorphous prewetting films on the grain boundaries in the ZnO:Bi2O3 system.

Non-conformal limit of AGT relation from the 1-point torus conformal block

Abstract: = 2 super symmetric Yang Mills (SYM) theories have attracted attention for rather a long time, because they are ideally suited for the study of interplay between perturbative and non perturbative effects and for manifestation of various dualities [1–4]. Depend ing on the fields content, these theories exhibit all types of renormalization behaviour of effective cou pling constant g: it may tend to infinity (Landau pole), and to zero (asymptotic freedom with dimensional transmutation in IR) or remain constant (UV finite).

On the collisions between particles in the vicinity of rotating black holes

Abstract: Scattering of particles in the gravitational field of rotating black holes is considered. It is shown that scattering energy of particles in the centre of mass system can obtain very large values not only for extremal black holes but also for nonextremal ones. Extraction of energy after the collision is investigated. It is shown that due to the Penrose process the energy of the particle escaping the hole at infinity can be large. Contradictions in the problem of getting high energetic particles escaping the black hole are resolved.

Spectrum of Kelvin-wave turbulence in superfluids

Abstract: We derive a type of kinetic equation for Kelvin waves on quantized vortex filaments with random large-scale curvature, that describes step-by-step (local) energy cascade over scales caused by 4-wave interactions. Resulting new energy spectrum ELN(k) ∝ k−5/3 must replace in future theory (e.g., in finding the quantum turbulence decay rate) the previously used spectrum EKS(k) ∝ k−7/5, which was recently shown to be inconsistent due to nonlocality of the 6-wave energy cascade.

Effect of the atomic composition of the surface on the electron surface states in topological insulators A{ 2 / V }B{ 3 / VI }

Abstract: The results of the theoretical investigation of the surface electronic structure of A 2 V B 3 VI compounds containing topologically protected surface states are reported. The ideal Bi2Te3, Bi2Se3, and Sb2Te3 surfaces and surfaces with an absent external layer of chalcogen atoms, which were observed experimentally as monolayer terraces, have been considered. It has been shown that the discrepancy between the calculated Fermi level and the value measured in the photoemission experiments can be attributed to the presence of the “dangling bond” states on the surface of the terraces formed by semimetal atoms. The fraction of such terraces on the surface has been estimated.

Strength properties of an aluminum melt at extremely high tension rates under the action of femtosecond laser pulses

Abstract: The dynamics of the melting of a surface nanolayer and the formation of thermal and shock waves in metals irradiated by femtosecond laser pulses has been investigated both experimentally and theoretically. A new experimental-computational method has been implemented to determine the parameters of laser-induced shock waves in metallic films. Data on the strength properties of the condensed phase in aluminum films at an extremely high strain rate (\( \dot V \)/V ∼ 109 s−1)under the action of a laser-induced shock wave have been obtained.

Topological superfluid 3He-B in magnetic field and ising variable

Abstract: The topological superfluid 3He-B provides many examples of the interplay of symmetry and topology. Here we consider the effect of magnetic field on topological properties of 3He-B. Magnetic field violates the time reversal symmetry. As a result, the topological invariant supported by this symmetry ceases to exist; and thus the gapless fermions on the surface of 3He-B are not protected any more by topology: they become fully gapped. Nevertheless, if perturbation of symmetry is small, the surface fermions remain relativistic with mass proportional to symmetry violating perturbation—magnetic field. The 3He-B symmetry gives rise to the Ising variable I = ±1, which emerges in magnetic field and which characterizes the states of the surface of 3He-B. This variable also determines the sign of the mass term of surface fermions and the topological invariant describing their effective Hamiltonian. The line on the surface, which separates the surface domains with different I, contains 1 + 1 gapless fermions, which are protected by combined action of symmetry and topology.

Topological invariants for Standard Model: from semi-metal to topological insulator

Abstract: We consider topological invariants describing semimetal (gapless) and insulating (gapped) states of the quantum vacuum of Standard Model and possible quantum phase transitions between these states.

Orbital glass and spin glass states of 3He-A in aerogel

Abstract: Glass states of superfluid A-like phase of 3He in aerogel induced by random orientations of aerogel strands are investigated theoretically and experimentally. In anisotropic aerogel with stretching deformation two glass phases are observed. Both phases represent the anisotropic glass of the orbital ferromagnetic vector I—the orbital glass (OG). The phases differ by the spin structure: the spin nematic vector \( \hat d \) can be either in the ordered spin nematic (SN) state or in the disordered spin-glass (SG) state. The first phase (OG-SN) is formed under conventional cooling from normal 3He. The second phase (OG-SG) is metastable, being obtained by cooling through the superfluid transition temperature, when large enough resonant continuous radio-frequency excitation is applied. NMR signature of different phases allows us to measure the parameter of the global anisotropy of the orbital glass induced by deformation.

Direct bandgap optical transitions in Si nanocrystals

Abstract: The effect of quantum confinement on the direct bandgap of spherical Si nanocrystals has been modelled theoretically. We conclude that the energy of the direct bandgap at the Γ-point decreases with size reduction: quantum confinement enhances radiative recombination across the direct bandgap and introduces its “red“ shift for smaller grains. We postulate to identify the frequently reported efficient blue emission (F-band) from Si nanocrystals with this zero-phonon recombination. In a dedicated experiment, we confirm the “red“ shift of the F-band, supporting the proposed identification.

Anion height dependence of T c and the density of states in iron-based superconductors

Abstract: Systematic ab initio LDA calculations were performed for all the typical representatives of recently discovered class of iron-based high-temperature superconductors: REOFe(As,P) (RE = La, Ce, Nd, Sm, Tb), Ba2Fe2As, (Sr,Ca)FFeAs, Sr4Sc2O6Fe2P2, LiFeAs and Fe(Se,Te). Non-monotonic behavior of total density of states at the Fermi level is observed as a function of anion height relative to Fe layer with maximum at about Δz a ∼ 1.37 A, attributed to changing Fe-As (P, Se, Te) hybridization. This leads to a similar dependence of superconducting transition temperature T c as observed in the experiments. The fit of this dependence to elementary BCS theory produces semiquantitative agreement with experimental data for T c for the whole class of iron-based superconductors. The similar fit to Allen-Dynes formula underestimates T c in the vicinity of the maximum, signifying the possible importance of non-phonon pairing in this region. These results unambiguously demonstrate that the main effect of T c variation between different types of iron-based superconductors is due to the corresponding variation of the density of states at the Fermi level.

Contribution of light-by-light scattering to energy levels of light muonic atoms

Abstract: The complete contribution of diagrams with the light-by-light scattering to the Lamb shift is found for muonic hydrogen, deuterium and helium ion. The results are obtained in the static-muon approximation and a part of the paper is devoted to the verification of this approximation and analysis of its uncertainty.

Towards a solution of the cosmological constant problem

Abstract: The standard model of elementary particle physics and the theory of general relativity can be extended by the introduction of a vacuum variable which is responsible for the near vanishing of the present cosmological constant (vacuum energy density). The explicit realization of this vacuum variable can be via a three-form gauge field, an aether-type velocity field, or any other field appropriate for the description of the equilibrium state corresponding to the Lorentz-invariant quantum vacuum. The extended theory has, without fine-tuning, a Minkowski-type solution of the field equations with spacetime-independent fields and provides, therefore, a possible solution of the main cosmological constant problem.

Ferromagnetic effect of a Mn delta layer in the GaAs barrier on the spin polarization of carriers in an InGaAs/GaAs quantum well

Abstract: The polarization properties of the luminescence of an undoped InGaAs quantum well in InGaAs/GaAs het-erojunctions with a Mn delta layer in the GaAs barrier have been studied in a wide range of temperatures and magnetic fields. It has been found that the s, p-d exchange interaction of carriers in the quantum well with Mn ions in the δ layer leads to the ferromagnetic behavior of both the Zeeman splitting and spin polarization of the carriers with a Curie temperature typical of the Mn delta layer in the GaAs barrier. The saturation of the spin polarization of holes associated with their Fermi degeneracy has been observed at low temperatures (T < 20 K).

Magnetocaloric properties of manganites in alternating magnetic fields

Abstract: The magnetocaloric effect has been measured in manganites of various chemical compositions in weak alternating magnetic fields. The capabilities of a simple method for measuring the magnetocaloric effect by modulating the magnetic field have been demonstrated. The dependence of the magnetocaloric effect on the temperature, magnetic field, and chemical composition of samples is interpreted.

Broadband blooming of a medium modified by an incorporated layer of nanocavities

Abstract: The optical properties of a dielectric medium with the ordered distribution of nanopores in the surface layer have been investigated. It has been shown that the presence of a single layer of nanocavities near the medium-vacuum interface can increase the transparency of the medium to values close to 100% in a wide wavelength range.

Ternary thallium-based semimetal chalcogenides Tl-V-VI2 as a new class of three-dimensional topological insulators

Abstract: The results of the theoretical investigation of the bulk and surface electronic structures of Tl-V-VI2 compounds, where V is the Bi or Sb semimetal and VI is the Se or Te chalcogen, are reported. It has been shown that these compounds are three-dimensional topological insulators. Both a topologically protected surface state, which forms a Dirac cone at the \( \bar \Gamma \) point, and occupied surface states, which are localized in the band gap, are present on the surface of these compounds.

Non-Newtonian dynamics of the fast motion of a magnetic vortex

Abstract: The dynamics of a magnetic vortex in a thin magnetically soft ferromagnetic disc with a submicron diameter has been analyzed. Under the action of field pulses with a duration of the order of 10–100 ps, the vortex undergoes a complex motion. The analysis of the results of a micromagnetic simulation indicates that this motion is non-Newtonian. It can be described by an equation containing the third time derivative of the displacement of the vortex core.

On the shape of the gamma resonance spectra of slowly relaxing nanoparticles in a magnetic field

Abstract: A nonstandard shape of the gamma resonance spectra of nanoparticles in the form of inverted five-step pedestal has been predicted, observed, and analytically described. This shape corresponds to the limit of high temperatures and slow relaxation of the homogeneous magnetization of single-domain particles with axial magnetic anisotropy. To describe the Mossbauer spectra of the ensemble of chaotically oriented nanoparticles in a magnetic field, a continual magnetic-dynamics model has been developed in the limit of slow relaxation. This model adequately describes the polarization effects observed in the experimental absorption spectra. The revealed features significantly expand the methodical capabilities of Mossbauer spectroscopy for the diagnostics of magnetic nanomaterials.

Nonlocal effects in the electrodynamics of metallic slabs

Abstract: The influence of spatial dispersion and size on the interaction of a metallic slab with electromagnetic radiation has been studied in the model of the Boltzmann kinetic equation. It has been shown that the results are qualitatively different from those obtained in the Drude-Lorentz approximation. In particular, in the high-frequency region, the absorption oscillates with the radiation frequency and sample thickness. The absorption becomes sensitive to the Fermi velocity of electrons and depends nontrivially on the electron relaxation rate. The results may be useful for the analysis of the electromagnetic response of metal-dielectric micro- and nanostructures in the terahertz and/or infrared frequency range.

Search for macroscopic CP violating forces using a neutron EDM spectrometer

Abstract: The search for CP violating forces between nucleons in the so-called axion window of force ranges λ between 2 × 10−5 m and 0.02 m is interesting because only little experimental information is available there. Axionlike particles would induce a pseudo-magnetic field for neutrons close to bulk matter. A laboratory search investigates neutron spin precession close to a heavy mirror using ultracold neutrons in a magnetic resonance spectrometer. From the absence of a shift of the magnetic resonance we established new constraints on the coupling strength of axion-like particles in terms of the product g s g p of scalar and pseudo-scalar dimensionless constants, as a function of the force range λ, g s g p λ2 ≤ 2 × 10−21 [cm2] (C.L.95%) for 10−4 cm < λ < 1 cm. For 0.1 cm < λ < 1 cm previous limits are improved by 4 to 5 orders of magnitude.

Two-dimensional light bullets in an array of carbon nanotubes

Abstract: The problem of the propagation of two-dimensional solitary electromagnetic waves in an array of carbon nanotubes has been considered The electromagnetic field and the electron system of carbon nanotubes have been treated on the basis of the Maxwell’s equations and the Boltzmann kinetic equation in the relaxation-time approximation, respectively The derived effective equation has been analyzed and the state of the electromagnetic field that is localized in two spatial dimensions has been found

Elastic-plastic phenomena in ultrashort shock waves

Abstract: A physical model of shock-wave phenomena in metals irradiated by a femtosecond laser pulse has been developed. The use of the experimental results (reported in S.I. Ashitkov et al., Pis’ma Zh. Eksp. Teor. Fiz. 92, 568 (2010) [JETP Lett. 92, 516 (2010)] together with the molecular dynamics simulation makes it possible to study the elastic properties of aluminum crystals at extreme shear stresses comparable in amplitude with the shear modulus. As a result, the elastic Hugoniot adiabat has been continued to the region of metastable elastic states at very high pressures, which are one or two orders of magnitude higher than the commonly accepted values for the dynamic elastic limit. It has been shown that the ultrashort elastic shock wave of superhigh pressure precedes the formation of the known split-shock wave structure consisting of an elastic precursor and a plastic shock wave.

Study of the electronic structure of single-walled carbon nanotubes filled with cobalt bromide

Abstract: Single-walled carbon nanotubes have been filled with cobalt bromide. The microstructure, optical properties, and effect of the introduced CoBr2 compound on the electronic structure of the nanotubes have been studied. It has been shown that the electron density in the resulting nanocomposites is transferred from the walls of the nanotubes to the nanocrystals of cobalt bromide, which is an electron acceptor.

Polarizability exaltation of endofullerenes X@Cn (n = 20, 24, 28, 36, 50, and 60; X is a noble gas atom)

Abstract: The polarizability exaltation in molecules of endohedral complexes of C20, C24, C28, C36, C50, and C60 fullerenes with He, Ne, Ar, and Kr noble gas atoms has been revealed and studied by the density functional theory method. It has been found that the sign of the Δα polarizability exaltation depends on the number of atoms in a fullerene molecule.

Cluster self-organization of nanotubes in a nematic phase: The percolation behavior and appearance of optical singularities

Abstract: The structural features, as well as the optical and electrophysical properties of a 5CB nematic liquid crystal with additions of multilayer carbon nanotubes, have been investigated in the concentration range C = 0.0025–0.1 wt %. The self-aggregation of nanotubes into clusters with a fractal structure occurs in the liquid crystal. At 0.025 wt %, the clusters are merged, initiating the percolation transition of the composite to a state with a high electric conductivity. The strong interaction of 5CB molecules with the surface of nanotube clusters is responsible for the formation of micron surface liquid crystal layers with an irregular field of elastic stresses and a complex structure of birefringence. They are easily observed in a polarization microscope and visualize directly invisible submicron nanotube aggregates. Their transverse size increases when an electric field is applied to the liquid crystal cell. Two mechanisms of the generation of optical singularities in the passing laser beam have been revealed. Optical vortices appear in the speckle fields of laser radiation scattered at the indented boundaries of the nanotube clusters, whereas the birefringence of the beam in surface liquid-crystal layers is accompanied by the appearance of polarization C points.