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

POPRUZHENKO S.V. — 2014 г.

Using the imaginary time method, a new formulation of Coulomb corrections to the amplitude of nonlinear ionization of atoms is given. The Coulomb corrections to the photoelectron action and trajectory are presented in the form independent of the integration path in the imaginary time plane. The obtained representation corrects the previously known results and shows that the subdivision of photoelectron motion into the sub-barrier and after-barrier parts is conditional and does not influence observables. The new correction is particularly relevant in the multiphoton regime of ionization.

OUDOVENKO V.S., PLAKIDA N.M. — 2014 г.

We study d-wave superconductivity in the extended Hubbard model in the strong correlation limit for a large intersite Coulomb repulsion V. We argue that in the Mott-Hubbard regime with two Hubbard subbands, there emerges a new energy scale for the spin-fluctuation coupling of electrons of the order of the electronic kinetic energy W much larger than the exchange energy J. This coupling is induced by the kinematic interaction for the Hubbard operators, which results in the kinematic spin-fluctuation pairing mechanism for V < W. The theory is based on the Mori projection technique in the equation of motion method for the Green''s functions in terms of the Hubbard operators. The doping dependence of the superconductivity temperature T c is calculated for various values of U and V.

MISHRA S.R., RAWAT H.S., SINGH S., TIWARI V.B. — 2014 г.

A significant enhancement in the number of cold atoms in an atomic-beam-loaded magneto-optical trap (MOT) for metastable krypton atoms is observed when hollow laser beams are used in a Zeeman slower instead of a Gaussian laser beam. In the Zeeman slower setup, a combination of two hollow laser beams, i.e., a variablediameter hollow beam generated using a pair of axicon lenses superimposed on a fixed-diameter hollow beam, has been used to reduce the longitudinal velocity of the atoms in the atomic beam below the capture speed of the MOT. The observed enhancement in the number of atoms in the MOT is attributed to reduced destruction of the atom cloud in the MOT and increased cooling of the off-axis atoms in the atomic beam, resulting from the use of hollow beams in the Zeeman slower.

KUHNS P.L., REYES A.P., SAKHRATOV YU. A., SVISTOV L.E., ZHOU H.D. — 2014 г.

We measured 63,65Cu NMR spectra in a magnetic field up to about 15.5 T on a single crystal of the multiferroic triangular-lattice antiferromagnet CuCrCb. The measurements were performed for perpendicular and parallel orientations of the magnetic field with respect to the c-axis of the crystal, and the detailed angle dependence of the spectra on the magnetic field direction in the ab-plane was studied. The shape of the spectra can be well described in the model of spiral spin structure suggested by recent neutron diffraction experiments. When the field is rotated perpendicular to the crystal c-axis, we for the first time directly observed a remarkable reorientation of the spin plane simultaneous with rotation of the incommensurate wavevector, by quantitatively deducing the conversion of the energetically less favorable domain to a more favorable one. At high enough fields parallel to the c-axis, the data are consistent with either a field-induced commensurate spiral magnetic structure or an incommensurate spiral magnetic structure with a disorder in the с direction, suggesting that high fields may have influence on interplanar ordering.

GIRZHONA V.V., SMOLYAKOVA O.V., ZAKHARENKO M.I. — 2014 г.

We prove the possibility to use the method of modeling of a quasi-lattice with octagonal symmetry similar to that proposed earlier for the decagonal quasicrystal. The method is based on the multiplication of the groups of basis sites according to specified rules. This model is shown to be equivalent to the method of the periodic lattice projection, but is simpler because it considers merely two-dimensional site groups. The application of the proposed modeling procedure to the reciprocal lattice of octagonal quasicrystals shows a fairly good matching with the electron diffraction pattern. Similarly to the decagonal quasicrystals, the possibility of three-index labeling of the diffraction reflections is exhibited in this case. Moreover, the ascertained ratio of indices provides information on the intensity of diffraction reflections.

LONG H.N., VIEN V.V. — 2014 г.

A new S3 flavor model based on the SU(3)c®SU(3)l l'( I) \ gauge symmetry responsible for fermion masses and mixings different from our previous work [14.17] is constructed. The new feature is a two-dimensional representation of a Higgs anti-sextet under S3, which is responsible for neutrino masses and mixings. The neutrinos acquire small masses from only an anti-sextet of SU(3), which is in a doublet under S3. If the difference of components of the anti-sextet is regarded as a small perturbation, S3 is equivalently broken into identity, the corresponding neutrino mass mixing matrix acquires the most general form, and the model can fit the latest data on neutrino oscillations. This way of symmetry breaking helps us reduce a content in the Higgs sector, to only one anti-sextet instead of two as in our previous work [14]. Our results show that the neutrino masses are naturally small and a small deviation from the tri-bimaximal neutrino mixing form can be realized. The Higgs potential of the model as well as the minimization conditions and gauge boson masses and mixings are also considered.

ARSEEV P.I., MANTSEVICH V.N., MASLOVA N.S. — 2014 г.

We investigate the time evolution of filling numbers of localized electrons in the system of two coupled single-level quantum dots (QDs) connected with the continuous-spectrum states in the presence of Coulomb interaction. We considered correlation functions of all orders for electrons in the QDs by decoupling higher-order correlations between localized and band electrons in the reservoir. We analyze different initial charge configurations and consider Coulomb correlations between localized electrons both within the dots and between the different dots. We reveal the presence of a dynamical charge trapping effect in the first QD in the situation where both dots are occupied at the initial instant. We also find an analytic solution for the time-dependent filling numbers of the localized electrons for a particular configuration of the dots.

KUCHINSKII E.Z., KULEEVA N.A., SADOVSKII M.V. — 2014 г.

We study the normal (nonsuperconducting) phase of the attractive Hubbard model within the dynamical mean field theory (DMFT) using the numerical renormalization group (NRG) as an impurity solver. A wide range of attractive potentials U is considered, from the weak-coupling limit, where superconducting instability is well described by the BCS approximation, to the strong-coupling region, where the superconducting transition is described by Bose condensation of compact Cooper pairs, which are formed at temperatures much exceeding the superconducting transition temperature. We calculate the density of states, the spectral density, and the optical conductivity in the normal phase for this wide range of U, including the disorder effects. We also present the results on superconducting instability of the normal state dependence on the attraction strength U and the degree of disorder. The disorder influence on the critical temperature T c is rather weak, suggesting in fact the validity of Anderson''s theorem, with the account of the general widening of the conduction band due to disorder.

AVERIN D.V., DENG QIANG — 2014 г.

We have considered the quantum dynamics of an array of nSQUIDs - two-junction SQUIDs with negative mutual inductance between their two arms. Effective dual-rail structure of the array creates additional internal degree of freedom for the fluxons in the array, which can be used to encode and transport quantum information. Physically, this degree of freedom is represented by electromagnetic excitations localized on the fluxon. We have calculated the spatial profile and frequency spectrum of these excitations. Their dynamics can be reduced to two quantum states, so that each fluxon moving through the array carries with it a qubit of information. Coherence properties of such a propagating qubit in the nSQUID array are characterized by the dynamic suppression of the low-frequency decoherence due to the motion-induced spreading of the noise spectral density to a larger frequency interval.

ENNADIFI S.-E., LAAMARA R., LOUALIDI M.A. — 2014 г.

Motivated by the LHC results revealing the SM scalar sector as well as by its possible revision, we consider an MSSM scalar extension consisting of two Higgs triplets generating the observed neutrino and Higgs masses. The latter constrains their suppressed vevs and sizable couplings, which slightly influences the extended neutralino sector and the LSP emergence.

KHMELNITSKII D.E. — 2014 г.

Dielectric properties, thermal expansion, and the rate of spin-lattice relaxation at low temperatures in uniaxial dielectrics with a soft optical mode are discussed.

PALLE D. — 2014 г.

The first comprehensive analyses of Planck data reveal that the cosmological model with dark energy and cold dark matter can satisfactorily explain the essential physical features of the expanding Universe. However, the inability to simultaneously fit the large and small scale TT power spectrum, the scalar power index smaller than unity, and the observations of the violation of the isotropy found by few statistical indicators of the CM В urge theorists to search for explanations. We show that the model of the Einstein-Cartan cosmology with clustered dark matter halos and their corresponding clustered angular momenta coupled to torsion can account for small-scale-large-scale discrepancy and larger peculiar velocities (bulk flows) for galaxy clusters. The nonvanishing total angular momentum (torsion) of the Universe enters as a negative effective density term in the Einstein-Cartan equations causing partial cancellation of the mass density. The integrated Sachs-Wolfe contribution of the Einstein-Cartan model is negative, and it can therefore provide partial cancellation of the large-scale power of the TT CMB spectrum. The observed violation of the isotropy appears as a natural ingredient of the Einstein-Cartan model caused by the spin densities of light Majorana neutrinos in the early stage of the evolution of the Universe and bound to the lepton CP violation and matter-antimatter asymmetry.

AZAROV I.B., VESHCHUNOV M.S. — 2014 г.

A new approach to the diffusion-limited reaction kinetics for particles migrating by random walks on discrete lattice sites and reacting when two particles occupy the same site is extended to a more general case of a large reaction radius and applied to the problem of the recombination rate of point defects in cubic lattices. Numerical calculations correctly reproduce the analytic expressions in the limit cases considered in previous work and in the general case represent a step-wise dependence of the reaction rate on the recombination radius.

KAMANI D., ZOGHI M. — 2014 г.

We study open strings attached to a Dp-brane in the presence of the pp-wave background along with a constant antisymmetric В-field and the linear dilaton. The noncommutativity structure of this system is also investigated.

MARIS H.J., WEI W., XIE Z., YANG Y. — 2014 г.

A series of experiments has revealed the existence of a large number (about 18) of different types of negative ions in superfluid helium-4. Despite much effort, the physical nature of these "exotic ions" has still not been determined. We discuss possible experiments which may be able to help determine the structure of these objects.

FOMIN I.A. — 2014 г.

Highly anisotropic “nematically ordered" aerogel induces global uniaxial anisotropy in superfluid 3He. The anisotropy lowers symmetry of JHo in the aerogel from spherical to axial. As a result, instead of one transition temperature in a state with an orbital moment l = 1 there are two, corresponding to projections l z = 0 and l z= + -1 This splitting has a pronounced effect on the phase diagram of superfluid 3He and on the structures of the appearing phases. Possible phase diagrams, obtained phenomenologically on the basis of Landau expansion of the thermodynamic potential in the vicinity of the transition temperature are presented here. The order parameters corresponding to each phase and their temperature dependences are found.

RANI S., SHARIF M. — 2014 г.

We discuss the interacting f(T) gravity with pressureless matter in an FRW spacetime. We construct an f(T) model by following the correspondence scheme incorporating a recently developed pilgrim dark energy model and taking the Hubble horizon as the IR cutoff. We use constructed model to discuss the evolution trajectories of the equation-of-state parameter, the ώ т - ώ'' т phase plane, and state-finder parameters in the evolving universe. It is found that the equation-of-state parameter gives a phantom era of the accelerated universe for some particular range of the pilgrim parameter. The ώ т - ώ'' t plane represents freezing regions only for an interacting framework, while the ACDM limit is attained in the state-finder plane. We also investigate the first and second laws of thermodynamics assuming equal temperatures at and inside the horizon in this scenario. Due to the violation of the first law of thermodynamics in f(T) gravity, we explore the behavior of the entropy production term. The validity of a generalized second law of thermodynamics depends on the present-day value of the Hubble parameter.

ESCOBAR M., MEYEROVICH A.E. — 2014 г.

We discuss transport of particles along random rough surfaces in quantum size effect conditions. As an intriguing application, we analyze gravitationally quantized ultracold neutrons in rough waveguides in conjunction with GRANIT experiments (ILL, Grenoble). We present a theoretical description of these experiments in the biased diffusion approximation for neutron mirrors with both one- and two-dimensional (ID and 2D) roughness. All system parameters collapse into a single constant which determines the depletion times for the gravitational quantum states and the exit neutron count. This constant is determined by a complicated integral of the correlation function (CF) of surface roughness. The reliable identification of this CF is always hindered by the presence of long fluctuation-driven correlation tails in finite-size samples. We report numerical experiments relevant for the identification of roughness of a new GRANIT waveguide and make predictions for ongoing experiments. We also propose a radically new design for the rough waveguide.

MELNIKOVSKY L.A. — 2014 г.

Hidden symmetry in dissipationless terms of arbitrary hydrodynamics equations is recognized. We demonstrate that all fluxes are generated by a single function and derive conventional Euler equations using the proposed formalism.

FEL’DMAN E.B., ZENCHUK A.I. — 2014 г.

We investigate the Jordan-Wigner fermion clusters with a stationary distributed quantum pairwise discord. Such clusters appear after the Jordan-Wigner transformation of a spin chain governed by the nearest-neighbor XY Hamiltonian with the particular initial state having one polarized node. We show that the quantum discord stationarity in such systems is not destroyed by the “parasitic" polarization of at least two types. The first type appears because the initial state with a single polarized node is hardly realizable experimentally, and therefore the low polarization of neighboring nodes must be taken into account. The second is the unavoidable additional noise polarization of all nodes. Although the stationarity may not be destroyed by perturbations of the above two types, the parasitic polarizations deform the pairwise discord distribution and may destroy clusters of correlated fermions with equal pairwise discords. Such deformations are studied in this paper.