научный журнал по физике Журнал экспериментальной и теоретической физики ISSN: 0044-4510

JAWAD A., SHARIF M. — 2014 г.

We discuss the evolution of the newly proposed dark-energy model with a generalized event horizon (a generalized form of the holographic dark-energy model with a future event horizon) in the flat and nonflat universes. We consider the interacting scenario of this model with cold dark matter. We use the well-known logarithmic approach to evaluate the equation of state parameter and explore its present values. It is found that this parameter shows phantom crossing in some cases of the generalized event horizon parameters. The ώ-ώ plane is also developed for three different cases of the generalized event horizon parameters. The corresponding phase plane provides thawing and freezing regions. Finally, the validity of a generalized second law of thermodynamics is explored which holds in certain ranges of constant parameters.

FEDARUK P., MARKEVICH S.A., SAIKO A.P. — 2014 г.

We study the two-time correlation function and the resonance fluorescence spectrum of a semiconductor quantum dot excited by a strong off-resonant laser pulse. The obtained analytic expressions exhibit a specific detuning-dependent damping of Rabi oscillations of the dressed quantum dot as well as a detuning-dependent width of Mollow triplet lines. In the absence of pure dephasing, the central peak of the triplet is broadened upon increasing detuning, but the blue- and red-side peaks are narrowed. We demonstrate that the pure dephasing processes can invert these dependences. A crossover between the regimes of detuning-dependent narrowing and broadening of the side and central peaks is identified. The predicted effects are consistent with recent experimental results and numerical calculations.

KLAPWIJK T.M., RYABCHUN S.A. — 2014 г.

An overview is presented of experiments on ballistic electrical transport in inhomogeneous superconducting systems which are controlled by the process of Andreev reflection. The initial experiments based on the coexistence of a normal phase and a superconducting phase in the intermediate state led to the concept itself. It was followed by a focus on geometrically inhomogeneous systems like point contacts, which provided a very clear manifestation of the energy and direction dependence of the Andreev reflection process. The point contacts have recently evolved towards the atomic scale owing to the use of mechanical break-junctions, revealing a very detailed dependence of Andreev reflection on the macroscopic phase of the superconducting state. In present-day research, the superconducting inhomogeneity is constructed by clean room technology and combines superconducting materials, for example, with low-dimensional materials and topological insulators. Alternatively, the superconductor is combined with nano-objects, such as graphene, carbon nanotubes, or semiconducting nanowires. Each of these "inhomogeneous systems" provides a very interesting range of properties, all rooted in some manifestation of Andreev reflection.

CHUBANOV A.A., KHOMITSKY D.V. — 2014 г.

We derive a model of localized edge states in a finite-width strip for the two-dimensional electron gas formed in the hybrid system of a bismuth monolayer deposited on the silicon interface and described by the nearly free electron model with giant spin-orbit splitting. The edge states have the energy dispersion in the bulk energy gap with a Dirac-like linear dependence on the quasimomentum and the spin polarization coupled to the direction of propagation, demonstrating the properties of a topological insulator. The topological stability of edge states is confirmed by the calculations of the Z 2 invariant taken from the structure of the Pfaffian for the time reversal operator for the filled bulk bands in the surface Brillouin zone, which is shown to have a stable number of zeros with the variations of material parameters. The proposed properties of the edge states may support future advances in experimental and technological applications of this new material in nanoelectronics and spintronics.

CHAKRABORTY M., MISHRA M.K., PHUKAN A. — 2014 г.

It is observed experimentally that by injecting cold electrons in the discharge region of a double plasma device, the plasma parameters and sheath structure can be controlled in the other region, which is devoid of any electrical discharge. The main discharge region is separated from the region under investigation by a grounded mesh grid. Both cold and hot ionizing electrons are emitted from separate sets of filaments in the discharge region. With an increase in the cold electron emission current, the plasma parameters in the discharge region get changed, which in turn alter the plasma parameters in the other region. Two important effects caused by cold electrons in the diffusion region are the increase in the plasma density and decrease in the plasma potential. The increase in the plasma density and decrease in the sheath potential drop therefore cause the contraction of the sheath.

FALKOVSKY L.A. — 2014 г.

The theory of Raman scattering in half-metals by optical phonons interacting with conduction electrons is developed. We evaluate the effect of electron-phonon interactions at ferromagnetic ordering in terms of the Boltzmann equation for carriers. The chemical potential is found to decrease as the temperature decreases. Both the linewidth and frequency shift exhibit a dependence on temperature.

BABUSHKINA N.A., KALINOV A.V., KAMENEV A.A., KAUL A.R., KHOMSKII D.I., KUGEL K.I., KUZMOVA T.G., STRELTSOV S.V., TALDENKOV A.N. — 2014 г.

We study experimentally and theoretically the effect of Eu doping and partial oxygen isotope substitution on the transport and magnetic characteristics and spin-state transitions in (Рr 1-y Еu y) 0.7Са 0.3Со0 3 cobaltites. The Eu doping level у is chosen in the range of the phase diagram near the crossover between the ferromagnetic and spin-state transitions (0.10 < у < 0.20). We prepared a series of samples with different degrees of enrichment by the heavy oxygen isotope 180, namely, with 90%, 67%, 43%, 17%, and 0% of 180. Based on the measurements of the ac magnetic susceptibility x(T) and electrical resistivity p(T), we analyze the evolution of the sample properties with the change of the Eu and 180 content. It is demonstrated that the effect of increasing the 180 content on the system is similar to that of increasing the Eu content. The band structure calculations of the energy gap between t 2g and e g bands including the renormalization of this gap due to the electron-phonon interaction reveals the physical mechanisms underlying this similarity

ANDREEV B.A., ERSHOV A.V., GRACHEV D.A., GUSEV O.B., YABLONSKIY A.N. — 2014 г.

The effect of surface states of silicon nanocrystals embedded in silicon dioxide on the photoluminescent properties of the nanocrystals is reported. We have investigated the time-resolved and stationary photoluminescence of silicon nanocrystals in the matrix of silicon dioxide in the visible and infrared spectral ranges at 77 and 300 K. The structures containing silicon nanocrystals were prepared by the high-temperature annealing of multilayer SiO х/SiO 2 films. The understanding of the experimental results on photoluminescence is underlain by a model of autolocalized states arising on surface Si Si dimers. The emission of autocatalized excitons is found for the first time, and the energy level of the autolocalized states is determined. The effect of these states on the mechanism of the excitation and the photoluminescence properties of nanocrystals is discussed for a wide range of their dimensions. It is reliably shown that the cause of the known blue boundary of photoluminescence of silicon nanocrystals in the silicon dioxide matrix is the capture of free excitons on autolocalized surface states.

RAJABI A., RAZAVIFAR Z. — 2014 г.

The ground-state energy of polarized and unpolarized liquid JHo is calculated using the variational theory. A variational wave function is constrained to be normalized appropriately by including the three-body terms in the cluster expansion of the two-body radial distribution function. The higher-order terms have been found to be important to obtain an equation of state which is in agreement with experimental data. The saturation density of unpolarized liquid JHo was found to be 0.267-J, which decreases by enhancing the polarization. For all relevant densities, the ground-state energy of the spin case

MIKITIK G.P. — 2014 г.

The lower critical field H c1 in layered superconductors is calculated under the assumption that vortex pinning by point defects is strong in these materials. We consider the case of a purely electromagnetic coupling of vortex pancakes and the case of both the electromagnetic and Josephson couplings of the pancakes in a vortex line. In the latter case, singularities in the temperature dependence of H ci are predicted at certain characteristic temperatures.

TOBISCH E. — 2014 г.

We consider nonlinear gravity-capillary waves with the nonlinearity parameter s ~ 0.1-0.25. For this nonlinearity, time scale separation does not occur and the kinetic wave equation does not hold. An energy cascade in this case is built at the dynamic time scale (D-cascade) and is computed by the increment chain equation method first introduced in [15]. We for the first time compute an analytic expression for the energy spectrum of nonlinear gravity-capillary waves as an explicit function of the ratio of surface tension to the gravity acceleration. We show that its two limits - pure capillary and pure gravity waves on a fluid surface - coincide with the previously obtained results. We also discuss relations of the D-cascade model with a few known models used in the theory of nonlinear waves such as Zakharov''s equation, resonance of modes with nonlinear Stokes-corrected frequencies, and the Benjamin-Feir index. These connections are crucial in understanding and forecasting specifics of the energy transport in a variety of multicomponent wave dynamics, from oceanography to optics, from plasma physics to acoustics.

ARONSON M.C., IVANSHIN N.A., IVANSHIN V.A., LITVINOVA T.O., POPPL A., SOKOLOV D.A. — 2014 г.

We report electron spin resonance (ESR) experiments on the Heusler alloy YbRh 2Pb and compare its spin dynamics with that of several other Yb-based intermetallics. A detailed analysis of the derived ESR parameters indicates the extremely weak hybridization, more localized distribution of the 4f states, and a smaller RKKY interaction in YbRh 2Pb. These findings reveal the important interplay between hybridization effects, chemical substitution, and crystalline electric field interactions that determines the ground state properties of strongly correlated electron systems.

AFANAS’EV V.P., SMIRNOV B.M., ZHILYAEV D.A. — 2014 г.

General principles are discussed for a gas discharge plasma involving excited atoms where electron-atom collision processes dominate. It is shown that an optimal kinetic model of this plasma at not large electric field strengths may be based on the rate constants of quenching excited atom states by electron impact. The self-consistent character of atom excitation in gas discharge plasma is important and results in the tail of the energy distribution function of electrons being affected by the excitation process, which in turn influences the excitation rate. These principles are applied to an argon gas discharge plasma where excitation and ionization processes have a stepwise character and proceed via formation of argon atom states with the electron shell 3p 54s.

ALAYA S., ELGHOUL N., KHIROUNI K., ZEMZEMI M. — 2014 г.

Cuprous oxide is selected as a promising material for photovoltaic applications. Density functional theory is used to study the structural, electronic, and thermodynamic properties of cuprous oxide by using the local density approximation and generalized-gradient approximation. The effect of pressure on the structural and electronic properties of Cu 2O is investigated. This study confirms and characterizes the existence of new phases. Hexagonal and tetragonal phases are not completely indentified. We focus on the phase transition of the cuprous oxide under hydrostatic pressure to tetragonal and hexagonal (Cdb) structures. Variation of enthalpy with pressure is used to calculate the pressure of the phase transition.

NELSON D.K., RAZBIRIN B.S., ROZHKOVA N.N., SHEKA E.F., STARUKHIN A.N. — 2014 г.

Viewing shungite as loosely packed fractal nets of graphene-based (reduced graphene oxide, rGO) quantum dots (GQDs), we consider photoluminescence of the latter as a convincing proof of the structural concept as well as of the GQD attribution to individual rGO fragments. We study emission from shungite GQDs for colloidal dispersions in water, carbon tetrachloride, and toluene at both room and low temperatures. As expected, the photoluminescence of the GQD aqueous dispersions is quite similar to that of synthetic GQDs of the rGO origin. The morphological study of shungite dispersions shows a steady trend of GQDs to form fractals and to drastically change the colloid fractal structure caused by the solvent exchange. Spectral study reveals a dual character of the emitting centers: individual GQDs are responsible for the spectra position while the fractal structure of GQD colloids provides high broadening of the spectra due to structural in homogeneity, thus causing a peculiar dependence of the photoluminescence spectra on the excitation wavelength. For the first time, photoluminescence spectra of individual GQDs were observed in frozen toluene dispersions, which paves the way for a theoretical treatment of the GQD photonics.

BABICH L.P. — 2014 г.

Elementary processes capable of producing neutrons in a thunderstorm atmosphere are analyzed. The efficiency of nuclear fusion 2H( 2H,n) 3He, photonuclear reactions (ϒ,X n), electrodisintegration reactions n mА(е -, n) n-1 m A and reactions e -(p +,n)ν e opposite to the β-decay is evaluated. It is shown that an unrealistically strong electric field is required for the nuclear fusion to be responsible for the neutron production in the lightning channel. The generation of neutrons in a thunderstorm atmosphere is connected with photonuclear (ϒ,X n) and, at a much lower degree, electrodisintegration reactions, the relativistic runaway electron avalanches being primary parent processes.

DEHGHANPOUR H.R. — 2014 г.

We have generated Nd-Fe-B-C nanoparticles by Nd:YAG (1064 nm) laser irradiation in distilled water. Exposure times were 1, 5, and 10 min. Characterization of such nanoparticles in terms of their size distribution, shape, and chemical composition was carried out by transmission electron microscopy, energy-dispersive X-ray, and Fourier transform infrared spectroscopy. To investigate the nanoparticle stability, the size distribution of nanoparticles was measured two weeks after the nanoparticle generation, using dynamic light scattering. Investigations with the help of the atomic force microscope and magnetic force microscope showed other aspects of the generated nanoparticles.

ANAND L.F., BUBBLY S.G., GUDENNAVAR S.B., KERUR B.R. — 2014 г.

The K-shell X-ray intensity ratios, radiative and total vacancy transfer probablities of platinum, gold, and lead are measured by employing the 2π geometrical configuration and a weak gamma source, a simple method proposed previously by our group. The targets of Pt, Au and Pb were excited using ϒ-rays of weighted energy 123.6 keV from a weak 57 Co source and the emitted K-shell X-rays were detected using an HPGe X-ray detector spectrometer coupled to a 16k multichannel analyzer. The measured values of these parameters are compared with the theoretical values and experimental data of other researchers, finding a good agreement. Thus 2π-geometrical configuration method with a weak gamma source can be alternative simple method to measure various atomic parameters in the field of X-ray spectroscopy.

ANDREEV S.N., SHEVELKO V.P., TOLSTIKHINA I. YU., TUPITSYN I.I. — 2014 г.

The influence of relativistic effects, such as relativistic interaction and relativistic wave functions, on the electronloss cross sections of heavy and superheavy atoms and ions (atomic number Z > 92) colliding with neutral atoms is investigated using a newly created RICODE-M computer program. It is found that the use of relativistic wave functions changes the electron-loss cross section values by about 20-30% around the cross-section maximum compared to those calculated with nonrelativistic wave functions. At relativistic energies E > 200 MeV/u, the relativistic interaction between colliding particles leads to a quasiconstant behavior of the loss cross sections σrel/El ~ const, to be compared with the Born asymptotic law σBel/El ~ In E/E.

MILADINOVIC T.B., PETROVIC V.M. — 2014 г.

We discuss the effects of two different spatial and temporal laser beam profiles on the energy distribution of ionized photoelectrons. Two types of profiles of laser radiation, Gaussian and Lorentzian, are considered. The influence of the nonzero initial momentum of ejected photoelectrons is observed. We find that selection of the laser beam profile influences the maximal energy distribution. It is also shown that the nonzero initial electron momentum has a more significant influence for the Lorentzian beam profile.