Showing papers in "Jetp Letters in 1998"

How to determine an effective potential for a variable cosmological term

Abstract: It is shown that if a variable cosmological term in the present Universe is described by a scalar field with minimal coupling to gravity and with some phenomenological self-interaction potential V(ϕ), then this potential can be unambiguously determined from the following observational data: either from the behavior of density perturbations in dustlike matter component as a function of redshift (given the Hubble constant additionally), or from the luminosity distance as a function of redshift (given the present density of dustlike matter in terms of the critical value).

Ultrahigh-energy cosmic rays, superheavy long-lived particles, and matter creation after inflation

Abstract: Cosmic rays of the highest energy, above the Greisen-Zatsepin-Kuzmin (GZK) cutoff of the spectrum, may originate in decays of superheavy long-lived particles. We conjecture that these particles may be produced naturally in the early Universe from vacuum fluctuations during inflation and may constitute a considerable fraction of cold dark matter. We predict a new cutoff in the ultrahigh-energy cosmic ray spectrum E cutoff

Towards a universal nuclear density functional

Abstract: A new form of the nuclear energy-density functional for describing the ground-state properties of finite nuclei up to the drip lines and beyond is proposed. The volume part in this functional is fit to the Friedman-Pandharipande and Wiringa-Fiks-Fabrocini equation of state for the UV14 plus TNI model up to densities ρ≈1 fm−3 by a fractional expression in ρ which can be extended to higher densities while preserving causality. For inhomogeneous systems, a surface energy-density term is added, with two free parameters, which also has a fractional form like the Pade approximant containing (∇ρ)2 in both the numerator and denominator. In addition to the Coulomb direct and exchange interaction energy, an effective ρ-dependent Coulomb-nuclear correlation term is included with one more free parameter. A three-parameter fit to the masses and radii of real nuclei shows that the latter term gives a contribution to the Coulomb displacement energy of the same order of magnitude as the Nolen-Schiffer anomaly. The first self-consistent run with the proposed functional, performed for about 100 spherical nuclei, gives rms deviations from experiment of ≈1.2 MeV in the masses and ≈0.01 fm in the radii, which are about a factor of two better than those obtained with the Skyrme functionals or with the Gogny force. The extrapolation to the drip lines lies in between the ETFSI and the macroscopic-microscopic model predictions.

Low-frequency relativistic electromagnetic solitons in collisionless plasmas

Abstract: A relativistic electromagnetic soliton solution in the model of a one-dimensional, unbounded, cold, collisionless plasma is obtained without using the envelope approximation. The breaking of solitons with over-critical amplitudes is observed. The stability of undercritical solitons and the breaking of overcritical solitons are demonstrated by a particle-in-cell computer simulation.

Anomalous enhancement of DD reaction in Pd and Au/Pd/PdO heterostructure targets under low-energy deuteron bombardment

Abstract: Yields of protons emitted in the D+D reaction in Pd, Au/Pd/PdO, Ti, and Au foils are measured by a d E-E counter telescope for bombarding energies between 2.5 and 10 keV. The experimental yields are compared with those predicted from a parametrization of the cross section and stopping power at higher energies. It is found that for Ti and Au target the enhancement of the D(d,p)T reaction is similar to that observed with a deuterium gas target (several tens of eV). The dependence of the yields on the bombarding energy corresponds well to the screening potential parameters U s=250±15 eV for Pd and 601 ±23 eV for Au/Pd/PdO. Possible models of the enhancement obtained are discussed.

Effective spacetime and Hawking radiation from a moving domain wall in a thin film of 3 He-A

Abstract: An event horizon for “relativistic” fermionic quasiparticles can be constructed in a thin film of superfluid 3He-A. The quasiparticles see an effective “gravitational” field which is induced by a topological soliton of the order parameter. Within the soliton the “speed of light” crosses zero and changes sign. When the soliton moves, two planar event horizons (black hole and white hole) appear, with a curvature singularity between them. Aside from the singularity, the effective spacetime is incomplete at future and past boundaries, but the quasiparticles cannot escape there because the nonrelativistic corrections become important as the blueshift grows, yielding “superluminal” trajectories. The question of Hawking radiation from the moving soliton is discussed but not resolved.

Electrons and photons in mesoscopic structures: quantum dots in a photonic crystal

Abstract: The synthesis and properties of a photonic crystal doped with quantum dots are reported. The structure exhibits a two-stage self-organization of silica nanoparticles along with quantum confinement effects in semiconductor colloids. The interplay of electron and photon confinement results in controllable spontaneous emission from the mesoscopic structure.

Galactic anisotropy as signature of ``top-down'' mechanisms of ultrahigh-energy cosmic rays

Abstract: We show that “top-down” mechanisms of ultrahigh-energy cosmic rays which involve heavy relic particle-like objects predict a Galactic anisotropy of the highest-energy cosmic rays at the level of minimum ∼ 20%. This anisotropy is large enough to be either observed or ruled out in the next generation of experiments.

Diffusion of circularly polarized light in a disordered medium with large-scale inhomogeneities

Abstract: It is shown that in the presence of diffusion of electromagnetic waves in random media containing large discrete scatterers, circular polarization can persist even after the radiation flux is isotropized. For scattering exactly in the backward direction, this effect is manifested as an increase in the interference contribution to the cross-polarized component of the intensity as the size of the scatterers increases.

Effect of hole-hole scattering on the conductivity of the two-component 2D hole gas in GaAs/(AlGa)As heterostructures

Abstract: The temperature dependences of the zero-magnetic-field resistivity ρ and magnetoresistance of the 2D hole gas in GaAs/(AlGa)As heterostructures are investigated in the temperature interval 0.4–4.2 K. As the temperature T is increased, (i) the resistivity ρ grows with a decreasing derivative dρ/dT, and (ii) the positive magnetoresistance diminishes from about 40% at T=0.4 K to about 1% at T=4.2 K. The results are explained in terms of a temperature-dependent mutual scattering of the holes, accompanied by momentum transfer between two different spin-split subbands.

Manganites at low temperatures and light doping: band approach and percolation

Abstract: A tight-band model is employed for thee 2g orbitals in manganites. It is shown that a large intra-atomic Hund couplingJ H and the resulting double-exchange mechanism lead to antiferromagnetic ordering along one of the cubic axes, stabilized by the cooperative Jahn-Teller effect, which further decreases the band energy, of the electrons. As a result, LaMnO3 is a band insulator built of 2D ferromagnetic layers. The critical concentration (x c ≃0.16) for the onset of ferromagnetic and metallic behavior at low temperatures in La1−x Sr x MnO3 and the phase transition are treated in a percolation approach.

Destruction of localized electron pairs above the magnetic-field-driven superconductor-insulator transition in amorphous In-O films

Abstract: The field-induced superconductivity-destroying quantum transition in amorphous indium oxide films are investigated at low temperatures down to 30 mK. It is found that, on the high-field side of the transition, the magnetoresistance reaches a maximum and the phase can be insulating as well as metallic. With further increase of the magnetic field the resistance of the film drops and in the high-field limit approaches the resistance value at the transition point, so that at high fields the metallic phase occurs for both cases. We give a qualitative account of this behavior in terms of field-induced destruction of localized electron pairs.

First results of experiments on high-efficiency single-crystal extraction of protons from the U-70 accelerator

Abstract: A radical increase in the efficiency of beam extraction from an accelerator is achieved with a short (7 mm long) crystal bent by a small angle (17 mrad) by increasing the number of times particles pass through the crystal A particle extraction efficiency of ~20%, in agreement with the prediction of the theory, was achieved experimentally A record high intensity of the extracted beam 19×1011 protons per cycle, which is four orders of magnitude higher than previous results, is obtained

Matrix element of the anomalously low-energy (3.5±0.5 eV) transition in 229Th and the isomer lifetime

Abstract: The matrix element of the anomalously low-energy (3.5±0.5 eV) nuclear M1 transition between the first excited state and the ground state of the 229Th nucleus is determined with allowance for the Coriolis mixing of the rotational bands. The upper and lower limits on the lifetime of the level with respect to an isomeric transition are given. A method is proposed for measuring the half-life of the low-lying isomer 229mTh directly in a 233U sample.

Ground-state instability in systems of strongly interacting fermions

Abstract: The stability of a fermion system is analyzed for a model repulsive pair interaction potential. The possibility of different types of restructuring of the Fermi ground state (at sufficiently great coupling constant) is related to the analyticity properties of such potential. In particular, for the screened Coulomb law it is shown that the restructuring cannot be of the Fermi condensation type, known earlier for some exactly solvable models, but instead belongs to the class of topological transitions. A phase diagram constructed for this model in the variables “screening parameter-coupling constant” displays two kinds of topological transitions: a “5/2” kind, similar to the known Lifshitz transitions in metals, and a “2” kind, characteristic for a uniform strongly interacting system.

Magnetoexcitons in type-II quantum dots

Abstract: The ground state of a spatially indirect exciton in type-II quantum dots with a short-range potential acquires nonzero angular momentum in the presence of a magnetic field oriented perpendicular to the plane of the system The critical magnetic field of the transition to a ground state with nonzero angular momentum depends on the radius of the quantum dot Such a transition can be observed as quenching of luminescence by a magnetic field in quantum dots of the GaSb/GaAs system, for example

Hamiltonian dynamics of vortex lines in hydrodynamic-type systems

Abstract: It is shown that the degeneracy of the noncanonical Poisson bracket operating on the space of solenoidal vector fields that arises due to the freezing-in of the curl of the velocity [E. A. Kuznetsov and A. V. Mikhailov, Phys. Lett. A 77, 37 (1980)] is lifted when the vorticity Ω is represented in terms of vortex lines. This representation makes it possible to integrate the equation of motion of the vorticity for a system with the Hamiltonian H=∫∣Ω∣dr.

Gravity of monopole and string and gravitational constant in 3He-A

Abstract: We discuss the effective metric produced in superfluid 3He-A by such topological objects as the radial disgyration and monopole. In relativistic theories these metrics are similar to that of the local string and global monopole, respectively. But in 3He-A they have a negative angle deficit, which corresponds to a negative mass of the topological objects. The effective gravitational constant in superfluid 3He-A, deduced from a comparison with relativistic theories, is G∼Δ−2, where the gap amplitude Δ plays the part of the Planck energy. G depends on temperature roughly as (1−T 2/T 2 )−2 and corresponds to a screening of Newton’s constant.

Dynamics of self-similar dispersion-managed soliton presented in the basis of chirped Gauss-Hermite functions

Abstract: Applying chirped Gauss-Hermite orthogonal functions we present an analytical description of the breathing dynamics of the chirped dispersion-managed soliton. The theory describes both self-similar evolution of the central, energy-containing core and accompanying nonstationary oscillations of the far-field tails of an optical pulse propagating in a fiber line with arbitrary dispersion map.

Characteristic features of the x-ray spectra of a plasma produced by heating CO2 clusters by intense femtosecond laser pulses with λ=0.8 and 0.4 μm

Abstract: The x-ray spectra of a plasma produced by heating CO2 clusters with intense femtosecond laser pulses with λ=0.8 μm and λ=0.4 μm are investigated. Spatially resolved x-ray spectra of the cluster plasma are obtained. The observed characteristic features of the x-ray emission spectra show unequivocally that such a plasma contains quite a large relative number of ions (≃10−2–10−3) with energies of 0.1–1 MeV. The contour of the OVIII Lyα line is found to have characteristic features that are especially conspicuous when the clusters are heated with second-harmonic pulses. These features cannot be explained by any mechanisms known to the authors.

Estimates of electron-positron pair production in the interaction of high-power laser radiation with high-Z targets

Abstract: Electron-positron production processes occurring in the interaction of 1018–1020 W/cm2 laser radiation with high-Z targets are examined. Computational results are presented for the pair production and the positron yield from the target with allowance for the contribution of pair production processes due to electrons and bremsstrahlung photons. Monte Carlo simulations using the PRIZMA code confirm the estimates obtained. The possible positron yield from high-Z targets irradiated with 102–103 TW laser radiation is estimated to be 109–1011.

Electron paramagnetic resonance in a subsystem of structural defects as a factor in the plasticization of NaCl crystals

Abstract: A change in the macroplastic deformation rate and an increase in the travel distances of edge dislocations are observed in NaCl single crystals placed in crossed dc and rf magnetic fields. The magnetic-field frequencies at which softening maxima are observed correspond to the resonance frequencies of transitions between Zeeman sublevels in paramagnetic complexes of structural defects.

Anomalous proximity effect in d-wave superconductors

Abstract: The anomalous proximity effect between a d-wave superconductor and a thin disordered normal layer is studied theoretically in the framework of Eilenberger equations. It is shown that disorder of the quasiparticle reflection from this thin layer leads to the formation of an s-wave component localized near the boundary. The angular and spatial structure of the pair potential near the interface is studied.

Magnetic and structural transitions in La 1−x Sr x MnO 3 : T-x phase diagram

Abstract: The electrical conductivity, magnetic susceptibility, magnetization, and submillimeter (v=5∓20 cm−1) permittivity and dynamic conductivity of La1−x Sr x MnO3 (0≤x≤ 0.45) single crystals are investigated. The anomalies in the temperature dependences of these quantities are identified with diverse magnetic and structural phase transformations, including antiferromagnetic and ferromagnetic ordering, structural transitions between strongly distorted (Jahn-Teller) and weakly distorted (pseudocubic) orthorhombic phases, structural transitions to a rhombohedral phase and unusual transitions to a polaron-ordering state. As a result, the complete T-x phase diagram of the system La1−2x Sr x MnO3 is constructed in a wide interval of temperatures T=4.2∓1050 K and concentrations x=0−0.45.

Diffractive vector mesons beyond the s-channel helicity conservation

Abstract: We derive a full set, and determine the twist, of helicity amplitudes for diffractive production of light to heavy vector mesons in deep inelastic scattering. For large Q2 all helicity amplitudes but the double-flip are calculable in perturbative QCD and are proportional to the gluon structure function of the proton at a similar hardness scale. We find a substantial breaking of the s-channel helicity conservation, which must persist in real photoproduction also.

Spontaneous far-IR emission accompanying transitions of charge carriers between levels of quantum dots

Abstract: The spontaneous emission of far-infrared radiation (λ≅10–20 μm) from diode structures with vertically coupled InGaAs/AlGaAs quantum dots is observed. This emission is due both to transitions of holes and electrons between size-quantization levels in quantum dots and to transitions from the continuum to a level in a quantum dot. It is observed only when accompanied by lasing at short wavelengths (λ≅0.94 μm) and, like the short-wavelength emission, it exhibits a current threshold. The spontaneous emission of long-wavelength radiation is also observed in InGaAs/GaAs quantum-well laser structures. This radiation is approximately an order of magnitude weaker than that from quantum-dot structures, and it has no current threshold.

Phase transitions in the ferromagnetic alloys Ni 2 + x Mn 1 - x Ga

Abstract: The phase diagram of the cubic ferromagnetic shape-memory alloy Ni2+x Mn1−x Ga is constructed theoretically for the case when the Curie temperature is close to the structural transition temperature. This diagram agrees well with the experimental data obtained from resistance and magnetic susceptibility measurements. It is shown that the transition from the paramagnetic cubic phase to the ferromagnetic tetragonal phase can be second-order or first-order.

Mechanism of field emission from carbon materials

Abstract: Field emission in diamond and graphite-like polycrystalline films is investigated experimentally. It is shown that the emission efficiency increases as the nondiamond carbon phase increases; for graphite-like films the threshold electric field is less than 1.5 V/μm, and at 4 V/μm the emission current reaches 1 mA/cm2, while the density of emission centers exceeds 106 cm−2. A general mechanism explaining the phenomenon of electron field emission from materials containing graphite-like carbon is proposed.

Self-organization of germanium nanoislands obtained in silicon by molecular-beam epitaxy

Abstract: Nanometer germanium islands in epitaxial layers of silicon are obtained by molecular-beam epitaxy. The dimensions and shapes of the islands are determined in an atomic-force microscope. The photoluminescence spectra are found to contain lines that can be interpreted as quasidirect optical transitions in the islands. It is concluded on the basis of optical and microprobe measurements and theoretical calculations of the energies of electronic states that silicon is dissolved in the germanium islands. Values of the germanium and silicon contents in the solid solution are presented.