Showing papers in "Jetp Letters in 2012"

Formation of nanocavities in the surface layer of an aluminum target irradiated by a femtosecond laser pulse

Abstract: It has been revealed experimentally that nanocavities remain inside a surface layer of aluminum after action of a femtosecond laser pulse. This result is in agreement with numerical simulation. A detailed picture of melting, formation of expansion and compression waves, and bubble nucleation in the stretched melt has been reconstructed through atomistic simulation. It has been shown that the bubbles do not fully collapse but remain as frozen disk-shaped nanocavities upon recrystallization of the melt. The formation of a porous metal with small voids is very important for understanding the physics of laser exposure and may have significant applications.

Magnetic switches based on Nb-PdFe-Nb Josephson junctions with a magnetically soft ferromagnetic interlayer

Abstract: The properties of Josephson junctions with a barrier made of a PdFe weakly ferromagnetic alloy with an iron content of about 1 at % have been studied. It has been shown that this alloy is a weak ferromagnet with a Curie temperature of 10–15 K in the required thickness range of 30–50 nm. The effect of the domain structure and magnetic prehistory of the ferromagnetic barrier on the critical current of a junction and the form of the Josephson characteristics has been demonstrated. The application of these junctions as magnetic switches has been proposed.

Topological Properties of Superconducting Junctions

Abstract: Motivated by recent developments in the field of one-dimensional topological superconductors, we investigate the topological properties of s-matrix of generic superconducting junctions where dimension should not play any role. We argue that for a finite junction the s-matrix is always topologically trivial. We resolve an apparent contradiction with the previous results by taking into account the low-energy resonant poles of s-matrix. Thus no common topological transition occurs in a finite junction. We reveal a transition of a different kind that concerns the configuration of the resonant poles.

Temperature-scanned magnetic resonance and the evidence of two-way transfer of a nitrogen nuclear spin hyperfine interaction in coupled NV-N pairs in diamond

Abstract: New method for the detection of magnetic resonance signals versus temperature is developed on the basis of the temperature dependence of the spin Hamiltonian parameters of the paramagnetic system under investigation. The implementation of this technique is demonstrated on the nitrogen-vacancy (NV) centers in diamonds. Single NV defects and their ensembles are suggested to be almost inertialess temperature sensors. The hyperfine structure of the 14N nitrogen nuclei of the nitrogen-vacancy center appears to be resolved in the hyperfine structure characteristic of the hyperfine interaction between NV and an N s center (substitutional nitrogen impurity) in the optically detected magnetic resonance spectra of the molecular NV-N s complex. Thus, we show that a direct evidence of the two-way transfer of a nitrogen nuclear spin hyperfine interaction in coupled NV-N s pairs was observed. It is shown that more than 3-fold enhancement of the NV optically detected magnetic resonance signal can be achieved by using water as a collection optics medium.

Phase diagram of superfluid 3 He in “nematically ordered” aerogel

Abstract: Results of experiments with liquid 3He immersed in a new type of aerogel are described. This aerogel consists of Al2O3 · H2O strands which are nearly parallel to each other, so we call it as a “nematically ordered” aerogel. At all used pressures a superfluid transition was observed and a superfluid phase diagram was measured. Possible structures of the observed superfluid phases are discussed.

Discrete breather on the edge of the graphene sheet with the armchair orientation

Abstract: Linear and nonlinear vibrations of a graphene nanoribbon with free armchair edges subjected to tensile deformation have been studied by atomistic simulation methods. It has been shown that the phonon modes are split into two subsets. Atoms in some (XY) modes vibrate in the nanoribbon plane and in other (Z) modes vibrate along the normal to this plane. The possibility of the excitation of a gap discrete breather in an extended nanoribbon in the spectrum of the Z modes, the frequency of which lies in the gap of the spectrum of the XY modes, has been demonstrated. This breather is a large-amplitude vibrational mode in the XY plane localized on the four atoms on the nanoribbon edge. The breather is unstable with respect to small perturbations in the form of displacements of atoms out of the nanoribbon plane. Nevertheless, the discrete breather decays slowly owing to its weak interaction with the Z modes, so that its lifetime can be on the order of 103 vibrational periods.

SANC integrator in the progress: QCD and EW contributions

Abstract: Modules and packages for the one-loop calculations at the partonic level represent the first level of SANC output computer product. The next level represents Monte Carlo integrator mcsanc, realizing fully differential hadron level calculations (convolution with PDF) for the HEP processes at LHC. In this paper we describe the implementation into the framework mcsanc first set of processes: DY NC, DY CC, $$f_1 \bar f'_1 \to HW^ \pm (Z)$$ and single top production. Both EW and QCD NLO corrections are taken into account. A comparison of SANC results with those existing in the world literature is given.

Dusty plasma system in the surface layer of the illuminated part of the moon

Abstract: The dusty plasma system in the surface layer of the illuminated part of the Moon has been considered. The maximum height of the dust rise has been determined. It has been shown that a dead zone, where dust particles cannot rise over the surface of the Moon, is absent near a lunar latitude of 80°. The size and height distributions of dust have been determined.

Analysis and correction of the measurement of the neutron lifetime

Abstract: Corrections have been introduced into the result τβ = 885.4 ± 0.9stat ± 0.4syst s of our measurements of the neutron lifetime. The corrected value is τβ = 881.6 ± 0.8stat ± 1.9syst s.

New method of the directional modification of the electronic structure of single-walled carbon nanotubes by filling channels with metallic copper from a liquid phase

Abstract: A method has been proposed and successfully implemented for filling the channels of single-walled carbon nanotubes with metallic copper by permeating with an aqueous solution of copper nitrate with subsequent thermal treatment. It has been demonstrated that the introduction of metallic copper into the channels of nanotubes leads to donor doping accompanied both by an increase in the Fermi energy of nanotubes and by the transfer of the electron density from introduced metal nanoparticles to the walls of nanotubes.

Giant Rashba-type spin splitting at polar surfaces of BiTeI

Abstract: On the basis of relativistic ab initio calculations, we show that both Te- and I-terminated surfaces of the polar layered semiconductor BiTeI hold surface states with a giant Rashba-type spin splitting. The Te-terminated surface state has nearly isotropic free-electron-like dispersion with a positive effective mass, which along with the giant spin splitting makes BiTeI fulfilling the requirements demanded by many semiconductor-spintronics applications. The I-terminated surface state with its negative effective-mass dispersion reproduces nicely the situation with the Rashba-split surface state on surfaces of noble-metal based surface alloys. The crucial advantage of BiTeI as compared with the surface alloys is the location of the I-terminated surface state in a quite wide band gap.

Electroluminescence of CdSe/CdS quantum dots and the transfer of the exciton excitation energy in an organic light-emitting diode

Abstract: A light emitting diode has been developed on the basis of multilayer nanostructures in which CdSe/CdS semiconductor colloidal quantum dots serve as emitters. Their absorption, photo-, and electroluminescence spectra have been obtained. The strong influence of the size effect and the density of particles in the layer on the spectral and electrophysical characteristics of the diode has been demonstrated. It has been shown that the rates of the transfer of the exciton excitation energy from organic molecules to quantum dots increase strongly even at a small increase in the radius of the core (CdSe) of a particle and depend strongly on the thickness of the shell (CdS) of the particle. The optimal arrangement of the layer of quantum dots with respect to the p-n junction has been estimated from the experimental data. The results demonstrate that the spectral characteristics and rates of the electron processes in light-emitting devices based on quantum dots incorporated into an organic matrix can be efficiently controlled.

Consistent LDA’ + DMFT—an unambiguous way to avoid double counting problem: NiO test

Abstract: We present a consistent way of treating a double counting problem unavoidably arising within the LDA + DMFT combined approach to realistic calculations of electronic structure of strongly correlated systems. The main obstacle here is the absence of systematic (e.g., diagrammatic) way to express LDA (local density approximation) contribution to exchange correlation energy appearing in the density functional theory. It is not clear then, which part of interaction entering DMFT (dynamical mean-field theory) is already taken into account through LDA calculations. Because of that, up to now there is no accepted unique expression for the double counting correction in LDA + DMFT. To avoid this problem we propose here the consistent LDA’ + DMFT approach, where LDA exchange correlation contribution is explicitly excluded for correlated states (bands) during self-consistent band structure calculations. What is left out of Coulomb interaction for those strongly correlated states (bands) is its non-local part, which is not included in DMFT, and the local Hartreelike contribution. Then the double counting correction is uniquely reduced to the local Hartree contribution. Correlations for strongly correlated states are then directly accounted for via the standard DMFT. We further test the consistent LDA’ + DMFT scheme and compare it with conventional LDA + DMFT calculating the electronic structure of NiO. Opposite to the conventional LDA + DMFT our consistent LDA’ + DMFT approach unambiguously produces the insulating band structure in agreement with experiments.

Electronic structure of nonstoichiometric compounds in the coherent potential approximation

Abstract: We formulate and implement a method for electronic structure calculations based on the coherent potential approximation. This method provides an accurate description for nonstoichiometric compounds with the disordered location of vacancies. In the essence of its formulation, the method is similar to the implementation of the local electron density approximation in combination with the dynamical mean field theory (LDA + DMFT) and, hence, it can be easily incorporated in the latter approach. We study the evolution of the electronic structure of titanium dioxide TiO2 − δ (rutile) with the growth of nonstoichiometry in the oxygen sublattice. The results of the calculations are compared to the experimental data on the photoemission spectra.

Constraints on the axion-electron coupling constant for solar axions appearing owing to bremsstrahlung and the compton process

Abstract: The axio-electric effect in silicon atoms is sought for solar axions appearing owing to bremsstrahlung and the Compton process. Axions are detected using a Si(Li) detector placed in a low-background setup. As a result, a model-independent constraint on the axion-electron coupling constant |g Ae | ≤ 2.2 × 10−10 has been obtained, which leads to the bounds m A ≤ 7.9 eV and m A ≤ 1.4 eV (at 90% C.L.) for the mass of the axion in the DFSZ and KSVZ models, respectively.

Electronic and magnetic structure of a possible iron based superconductor BaFe2Se3

Abstract: We present results of LDA calculations (band structure, densities of states, Fermi surfaces) for possible iron based superconductor BaFe2Se3 (Ba123) in normal (paramagnetic) phase. Results are briefly compared with similar data on prototype BaFe2As2 and (K,Cs)Fe2Se2 superconductors. Without doping this system is anti-ferromagnetic with TNexp ∼ 250 K and rather complicated magnetic structure. Neutron diffraction experiments indicated the possibility of two possible spin structures (antiferromagnetically ordered “plaquettes” or “zigzags”), indistinguishable by neutron scattering. Using LSDA calculated exchange parameters we estimate Neel temperatures for both spin structures within the molecular field approximation and show τ1 (plaquettes) spin configuration to be more favorable than τ2 (zigzags).

Cyclotron resonance of Dirac ferions in HgTe quantum wells

Abstract: Cyclotron resonance of single-valley two-dimensional Dirac fermions in HgTe-based quantum wells has been experimentally investigated. The thickness of the wells is close to the critical value corresponding to the transition from the direct energy spectrum to the inverted spectrum. Under terahertz laser irradiation, transitions between the ground and first Landau levels, as well as between the first and second Landau levels, have been observed. Low magnetic fields corresponding to the cyclotron resonance, as well as the strong dependence of the position of the resonance on the electron density, indicate the Dirac character of the spectrum in these quantum wells. It has been shown that disorder plays an important role in the formation of the spectrum of two-dimensional Dirac fermions.

Observation of a dispersion transition and the stability of a liquid in a nanoporous medium

Abstract: It has been found that the removal of overpressure is accompanied by a transition of some nonwetting-liquid nanoclusters to the stable state in narrow ranges of the filling factor and temperature. This means that the nonwetting liquid becomes “wetting.”

Universal crossover of liquid dynamics in supercritical region

Abstract: We demonstrate that all liquids in supercritical region may exist in two qualitatively different states: solid-like and gas-like. Solid-like to gas-like crossover corresponds to the condition τ ≈ τ0, where τ is liquid relaxation time and τ0 is the minimum period of transverse waves. This condition corresponds to the loss of shear stiffness of a liquid at all frequencies and defines a new narrow crossover zone on the phase diagram. We show that the intersection of this zone corresponds to the disappearance of high-frequency sound, qualitative changes of diffusion and viscous flow, increase in particle thermal speed to half of the speed of sound and reduction of the specific heat at constant volume to 2k B per particle. The new crossover is universal: it separates two liquid states at arbitrarily high pressure and temperature, and even exists in systems where liquid-gas transition and the critical point are absent overall.

Splitting of the electromagnetically induced transparency resonance on 85 Rb atoms in strong magnetic fields up to the Paschen-Back regime

Abstract: Electromagnetically induced transparency (EIT) resonance in strong magnetic fields of up to 1.7 kG has been investigated with the use of a 30-μm cell filled with an atomic rubidium vapor and neon as a buffer gas. The EIT resonance in the Λ system of the D1 line of 85Rb atoms has been formed with the use of two narrowband (∼1 MHz) 795-nm diode lasers. The EIT resonance in a longitudinal magnetic field is split into five components. It has been demonstrated that the frequencies of the five EIT components are either blue- or red-shifted with an increase in the magnetic field, depending on the frequency νP of the probe laser. In has been shown that in both cases the 85Rb atoms enter the hyperfine Paschen-Back regime in magnetic fields of >1 kG. The hyperfine Paschen-Back regime is manifested by the frequency slopes of all five EIT components asymptotically approaching the same fixed value. The experiment agrees well with the theory.

Diffraction of Electrons in the CubicTi 5 O 5 Superstructure of Titanium Monoxide

Abstract: Annealed titanium monoxide TiO1.087 has been studied by the electron diffraction method. A cubic model of the Ti5O5 superstructure (Ti5O5 (Ti90▪18O90□18)) of nonstoichiometric titanium monoxide Ti x O z has been proposed on the basis of experimental data and representations about the disorder-order transition channel. It has been shown that reflections observed on the electron diffraction pattern are identified in the space group $$Pm\bar 3m$$ . The period of the unit cell of the cubic Ti5O5 superstructure is larger than that for the B1 basic disordered structure of Ti x O z monoxide by a factor of 3. The disorder-order transition channel Ti x O z (space group $$Fm\bar 3m$$ )-Ti5O5 (space group $$Pm\bar 3m$$ ) includes 75 superstructure vectors of seven stars {k 10}, {k 7}, {k 6(1)}, {k 6(2)}, {k 4(1)}, {k 4(2)}, and {k 1}. The distribution functions of Ti and O atoms over the sites of the cubic Ti5O5 (space group $$Pm\bar 3m$$ ) superstructure have been calculated.

Pseudogap phase in cuprates: Oxygen orbital moments instead of circulating currents

Abstract: Circulating current loops within the cuprate unit cell are proposed to play a key role in the physics of the pseudogap phase. However, main experimental observations motivated by this sophisticated proposal and seemingly supporting the circulating current model can be explained within a simple and physically clear microscopic model. It has been argued that, instead of a well-isolated Zhang-Rice (ZR) singlet 1 A 1g , the ground state of the hole center [CuO4]5− (cluster analog of Cu3+ ion) in cuprates should be described by a complex 1 A 1g -1,3 B 2g -1,3 E u multiplet, formed by a competition of conventional hybrid Cu 3d-O 2p $$b_{1g} (\sigma ) \propto d_{x^2 - y^2 }$$ state and purely oxygen nonbonding O 2pπ states with a 2g (π) and e ux, y (π) symmetry. In contrast to inactive ZR singlet we arrive at several novel competing orbital and spin-orbital order parameters, e.g., Ising-like net orbital magnetic moment, orbital toroidal moment, intra-plaquette’s staggered order of Ising-like oxygen orbital magnetic moments. As a most impressive validation of the non-ZR model we explain fascinating results of recent neutron scattering measurements that revealed novel type of magnetic ordering in pseudogap phase of several hole-doped cuprates.

On the nonlinear Schrödinger equation for waves on a nonuniform current

Abstract: A nonlinear Schrodinger equation with variable coefficients for surface waves on a large-scale steady nonuniform current has been derived without the assumption of a relative smallness of the velocity of the current. This equation can describe with good accuracy the loss of modulation stability of a wave coming to a counter current, leading to the formation of so-called rogue waves. Some theoretical estimates are compared to the numerical simulation with the exact equations for a two-dimensional potential motion of an ideal fluid with a free boundary over a nonuniform bottom at a nonzero average horizontal velocity.

Theoretical study of the magnetic properties of ordered vacancies in 2D hexagonal structures: Graphene, 2D-SiC, and h-BN

Abstract: The magnetic properties of vacancies in 2D hexagonal structures—graphene and 2D-SiC and h-BN monolayers—have been studied. It has been found that a local magnetic moment exists in all listed systems in the presence of vacancies. However, in 2D hexagonal silicon carbide, the local magnetic moment appears only in the presence of silicon vacancy. In addition, the effect of the distance between vacancies in a monolayer on transitions between the ferromagnetic and antiferromagnetic states has been revealed.

Quantum electrodynamics with anisotropic scaling: Heisenberg-Euler action and Schwinger pair production in the bilayer graphene

Abstract: We discuss quantum electrodynamics emerging in the vacua with anisotropic scaling. Systems with anisotropic scaling were suggested by Hořava in relation to the quantum theory of gravity. In such vacua, the space and time are not equivalent, and moreover they obey different scaling laws, called the anisotropic scaling. Such anisotropic scaling takes place for fermions in bilayer graphene, where if one neglects the trigonal warping effects the massless Dirac fermions have quadratic dispersion. This results in the anisotropic quantum electrodynamics, in which electric and magnetic fields obey different scaling laws. Here we discuss the Heisenberg-Euler action and Schwinger pair production in such anisotropic QED.

Ultrafast electron dynamics on the silicon surface excited by an intense femtosecond laser pulse

Abstract: The electron dynamics on the silicon surface during the pump ultrashort infrared laser pulse is studied by time-resolved optical microscopy and electron-emission measurements. It is found that the optical response of the material under the conditions where a dense electron-hole plasma is formed is determined by the renormalization of the band spectrum of the material rather than by intraband transitions of photoexcited carriers. Nonlinear Auger recombination in the plasma enhanced by the plasma-induced renormalization of the band gap and accompanied by the generation of hot charge carriers stimulates intense prompt emission of such carriers from the surface of the photoexcited material, whose work function decreases owing to the large plasma-induced renormalization of the energies of higher conduction bands.

Transport relaxation time and quantum lifetime in selectively doped GaAs/AlAs heterostructures

Abstract: Low-temperature dependences of the transport relaxation time (τtr) and quantum lifetime (τq) on the density of the two-dimensional electron gas (n e ) in GaAs quantum wells with AlAs/GaAs lateral superlattice barriers have been studied. An exponential increase in the quantum lifetime with increasing electron density has been observed. It has been shown that the sharp increase in the quantum lifetime correlates with the appearance of X electrons in the AlAs/GaAs lateral superlattice barriers. It has been established that the ratio of the transport relaxation time to the quantum lifetime in the studied structures nonmonotonically depends on the density: the ratio τtr/τq first increases linearly with n e and then decreases. This behavior is not described by the existing theories.

Cylindrical and spherical electron-acoustic Gardner solitons and double layers in a two-electron-temperature plasma with nonthermal ions

Abstract: Cylindrical and spherical Gardner solitons (GSs) and double layers (DLs) in a two-electron-temperature plasma system (containing cold electrons, hot electrons obeying a Boltzmann distribution, and hot ions obeying a nonthermal distribution) are studied by employing the reductive perturbation method. The modified Gardner equation describing the nonlinear propagation of the electron-acoustic (EA) waves is derived, and its nonplanar GS and DL solutions are numerically analyzed. The parametric regimes for the existence of GSs, which are associated with both positive and negative potential, and DLs which are associated with positive potential, are obtained. The basic features of nonplanar EA GSs, and DLs, which are found to be different from planar ones, are also identified. The implications of our results in space and laboratory plasmas are briefly discussed.

Superluminal Neutrino and Spontaneous Breaking of Lorentz Invariance

Abstract: Generally speaking, the existence of a superluminal neutrino can be attributed either to re-entrant Lorentz violation at ultralow energy from intrinsic Lorentz violation at ultrahigh energy or to spontaneous breaking of fundamental Lorentz invariance (possibly by the formation of a fermionic condensate). Re-entrant Lorentz violation in the neutrino sector has been discussed elsewhere. Here, the focus is on mechanisms of spontaneous symmetry breaking.

Formation and evolution of dusty plasma structures in the ionosphere

Abstract: A self-consistent model of the formation and evolution of dusty plasma structures in the ionosphere has been developed The effect of the initial distributions of dust particles, as well as condensation and absorption of water molecules by dust particles, on the formation of noctilucent clouds and polar mesosphere summer echoes has been demonstrated The possibility of the formation of a layered structure of noctilucent clouds has been illustrated