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Using the method of molecular dynamics and taking Ni3Al and Pt3Al as examples, crystals of the A3B composition are considered for the possibility of excitation of soliton-type waves in them. The potentials obtained by the embedded-atom method were used to describe interatomic interactions. It is shown that the harmonic external stimulus can excite waves of the soliton type in a Pt3Al crystal, but not in Ni3Al. Such compression–expansion waves are generated because of excitation of discrete breathers with soft nonlinearity that cannot exist in a Ni3Al crystal near the affected region. The detected waves are capable of propagating to thousands of nanometers along the Pt3Al crystal without losses of integrity and speed. The shape of the obtained wave corresponds to the kink solution of the sine-Gordon equation. The aggregate amount of energy transferred by a wave is determined by the number of rows of atoms involved in fluctuations; this may involve dozens and hundreds of electron volts.

The effect of the nonlinear supratransmission in crystal of A3B stoichiometry is studied by molecular dynamics on the example of Pt3Al alloy. This effect is the transfer of energy at frequencies outside the phonon spectrum of the crystal. Research of the mechanisms of energy transport from the material surface to the interior is the important task, both from the theoretical point of view and from the prospects for practical application in the modification of near-surface layers by treatment with intense external influence of various types. The model was a three-dimensional face-centered cubic crystal whose atoms interact by means of the multiparticle potential obtained by the embedded atom method, which provides greater realism of the model in comparison with the use of pair potentials. Various forms of oscillation of the external influence region are considered. The possibility of energy transport from the crystal surface to the interior is shown by excitation of quasi-breathers near the region of influence and their subsequent destruction in the crystal and scattering of the energy stored on them. The quasibreathers are high-amplitude nonlinear atoms' oscillations of the alloy lightweight component at frequencies outside the phonon spectrum of the crystal. This effect was observed not with every oscillation's form of the region of influence. Quasi-breathers appeared most intensely near the region of influence with sinusoidal form oscillations. The results obtained indicate that the contribution of quasi-breathers to the energy transfer through the crystal increases with increasing amplitude of the influence. The range of amplitudes from 0.05 to 0.5 Å is considered. The frequency of the influence varied from 0.2 to 15 THz, which ensured the coverage of the entire spectrum of lowamplitude oscillations for this crystal's model. The minimum magnitude of the external effect amplitude at which this effect was observed was found to be 0.15 Å. At amplitudes greater than 0.5 Å, the cell rapidly decays for frequencies close to the optical branch of the phonon spectrum. The results of the study can be useful for laser processing of materials, surface treatment by low-energy plasma, and also in radiation materials science.

The research of quasi-breather statistical characteristics in the model crystal of A3B stoichiometry is conducted by means of molecular dynamics method in the paper by the example of Pt3Al. The phonon spectrum of this model crystal, the dependences of mean-square deviation, the coefficient of variation and the average frequency of the model quasi-breather on the time of its existence are obtained. The statistical data analysis allows for the conclusion that a quasi-breather model solution slightly differs from the exact breather corresponding to it in the model under consideration using the interatomic potential obtained by means of embedded atom method (EAM).

In this article, we study the structure of the network of dislocations near the boundary of a dicotyledonous bimetal Ni-Al under intense external harmonic influence. The method of molecular dynamics was chosen as the method, using potentials obtained by the immersed atom method. The paper analyzes the behavior of dislocation segments as a function of the intensity of exposure in the presence of vacancies near the boundary of a bipartite bimetal. It is shown that the frequency of exposure significantly affects the change in the structure of bimetal. In this case, point defects in the form of vacancies play an important role. The analysis was carried out by heating the calculated cells, the temperature of which is not more than half the melting temperature of the materials. Comparison with annealing of defects showed that structural changes in dislocations occur at lower temperatures, and their flow rate is higher.

Molecular dynamics is used in this work to study the energy transport through the CuAu crystal lattice by discrete breathers (DBs) with frequencies above the phonon spectrum. The DB moves along the close packed atomic row in the Cu sublattice. An asymmetry was introduced in the initial conditions used for DB excitation in order to set the DB in motion. The maximal distance travelled by the DB was calculated as the function of the asymmetry parameter. The results indicate a weak mobility of such objects in the considered CuAu crystal. Nevertheless, energy transport along the close-packed directions of the Cu sublattice is possible.

Energy localization in the ordered condensed systems is analyzed using А3В alloys with L12 superstructure. Using molecular dynamics, possible localization of phonon vibration energy in the aluminum sublattice and generation of a localized mode oscillating at a frequency belonging to the phonon spectrum energy gap and not representing a breather is considered for the ordered Pt3Al and Ni3Al alloys with L12 superstructure, which possess translational symmetry. Manifestations of anharmonicity in the atomic interactions and the relevant features of energy redistribution between sublattices of the ordered alloys are investigated. It is found out that in the ordered alloys of an A3B stoichiometry with L12 superstructure, whose phonon spectrum has a forbidden energy gap, vibrational energy can localize on the sublattice of B atoms. The alloys, found in a state of thermodynamic equilibrium at a certain temperature, are characterized by a local effect of spontaneous energy localization (the effect of energy redistribution between the lattices).

This article analyzes the structure and properties of the CuPt7 crystal for the possible existence of non-linear high-amplitude oscillations of the light alloy component. The densities of the phonon states of a crystal are calculated and analyzed for its different structures. It is demonstrated that the phonon system of a crystal has a narrow forbidden zone. The dependences of the possibility of the existence of high-amplitude oscillations on the initial conditions are revealed. It is shown that such oscillations are possible with the initial deviation of the Cu atom from the equilibrium position by more than 0.95 Å for FCC CuPt7. For such oscillators, their lifetime, the amount of stored energy, and other characteristics were obtained, which make it possible to characterize nonlinear high-amplitude lattice vibrations.

The singularities of an asymptotic representation of electromagnetic fields radiated in magnetoactive plasma with the parameters of the near-Earth ionosphere in the range of helical waves are investigated. The singular points of the dispersion surface of the refractive index of electromagnetic waves in the aforementioned range are determined. At these points, asymptotic representations are obtained for the intensity and power of the radiated electric field. The dependences of the directions of the vectors of the electromagnetic-wave group velocities on the directions of the wave phase velocities are found in the entire range of helical waves.

In the experiments at frequencies of less than the electron plasma frequency, the thermionic emission from the surface of an electric dipole in plasma causes the shunting of the capacitance of the double layer that surrounds the dipole. The most effective shunting is reached at the floating potential of the dipole arms.

A formula for the dynamical spin susceptibility of electron-doped high-temperature superconductors has been derived with the inclusion of strong correlation between localized and itinerant electrons. It provides an explanation of the basic features of inelastic neutron scattering in Pr0.88LaCe0.12CuO4−x with variation of the frequency and wave vector.

By method of molecular dynamics shows the possibility of moving discrete breathers with a hard type of nonlinearity along the crystal nanofibers Pt 3 Al. Consider the collision of discrete breathers with a hard type of nonlinearity, revealed that the interaction considered breathers cause partial dissipation of energy in the breather sublattice Al. The results may be useful in explaining the effects of low-dose and long-range effect. The possibility of the transfer of energy through the crystal over long distances can lead to structural transformation far away from the focus of excitation of these localized objects. They can will influence the transformation of the energy of the crystal structure, activate motion objects such as dislocations, Frenkel pairs or crowdion complexes.

In the framework of the singlet-correlated motion of holes over oxygen sites in CuO2 layers, a formula for the dynamic spin susceptibility has been derived taking into account the strong correlation between the magnetizations of the spins of the collective holes and localized moments on copper sites. The calculated behavior of the imaginary part of the susceptibility as a function of the frequency and wave vector is consistent with the available experimental data on the inelastic neutron scattering. The plot of the dispersion of the collective spin modes over the entire Brillouin zone is proposed.

The divergences, on cooling, of NMR-NQR relaxation rates and muon spin rotation in underdoped cuprates, until now interpreted in terms of glassy spin freezing of magnetic moments resulting from charge inhomogeneities, are critically reconsidered. The relaxation data are analyzed in the light of the lack of dependence from an external magnetic field, of the strength of the effective field driving the divergences and of the stretched exponential character of the recovery processes. By resorting also to the theoretical conclusions of the extended t-J model including the intersite Coulomb interactions, it is argued that the divergences of the relaxation rates, rather than arising from magnetic moments could be related to sliding motions of vortex-antivortex orbital currents coexisting with d-wave superconducting state.

Starting from the generalized t-J-G model Hamiltonian, we analyze the spin response in the superconducting cuprates taking into account both local and itinerant spin components which are coupled to each other self-consistently. Derived expression reproduces the basic observations of neutron scattering data in YBa2Cu3O6+y compounds near the optimal doping level., 9 pages, 6 figures. To be published in The European Physical Journal B (2012)

A compact expression has been obtained for the superexchange coupling of magnetic ions via intermediate anions with regard to polaron effects at both magnetic ions and intermediate anions. This expression is used to analyze the main features of the behavior of isotope shifts for temperatures of three types in layered cuprates: the Neel temperatures ($T_N$), critical temperatures of transitions to a superconducting state ($T_C$), and characteristic temperatures of the pseudogap in the normal state ($T^*$)., 4 pages, 1 figure

The distribution of magnetization in a semi-infinite single crystal of square cross section has been determined by means of micromagnetic modeling. It is established that both symmetric and asymmetric stable domain structures exist in the system in a broad range of variation of the magnetic anisotropy.

Two possible reasons for an instability with wave vector Q = (/gp,π) near the half-filling have been studied. The superexchange coupling of copper spins yields of-wave symmetry of the pseudogap. Nevertheless, the calculated critical temperature,T*, in this case is almost two times smaller than that observed experimentally in the bilayered cuprates. The phonon-mediated interaction (CDW scenario) provides the correct order of magnitude ofT*. As the symmetries of the pseudogaps differ in both cases, T* does not increase when we switch them on simultaneously.

Using the two relevant bands model, the temperature and doping dependences of the spin susceptibility La 2− x Sr x CuO 4 at T > T c have been calculated. The effect of strong correlations has been taken into account. We have found that model explains many features of the experimental data.

A formula for the dynamic spin susceptibility is derived in terms of the t-J-V model. This formula makes it possible to explain the main features of recent experiments on neutron scattering in the electron-doped superconductor Pr0.88LaCe0.12CuO4 − x. In particular, the proposed theory reproduces well a V-shaped relief in the frequency behavior of the imaginary part χ″(Q, ω) of the susceptibility of the Pr0.88LaCe0.12CuO4 − x compound in the vicinity of the wave vector Q = (π,π) and the scaling behavior of the position of the maxima in the dependence of the function χ″(Q, ω) T on the quantity ω/T. The magnetism of the high-temperature superconductors is dual. These materials contain charge carriers, on the one hand, and localized spins in the copper ion sublattice, on the other hand. Both these systems are strongly coupled to each other. The mode of collective oscillations is common. The magnetism of localized spins “freezes” with the appearance of the superconducting gap. The recently revealed double-peak structure of the imaginary part χ″(Q, ω) of the susceptibility in superconductors of the La1.84Sr0.16CuO4 type is explained. The low-frequency absorption peak is located within the superconducting gap and interpreted as a manifestation of the branch of spin excitons, and the high-frequency absorption peak predominantly corresponds to renormalized collective oscillations of localized spins.

We have derived an expression for the dynamical spin susceptibility of a hole-doped high-temperature superconductor taking into account a strong correlation between the magnetization of spins of the localized and itinerant electrons. This formula has been used to calculate the imaginary part of the susceptibility as a function of the frequency and wave vector. The results are compared to experimental data on the inelastic neutron scattering in compounds of the YBa2Cu3O6+y type. A peak in the scattering intensity observed at an energy of about 40 meV in the region of wave vectors Q = (π, π) and an arc-shaped dispersion relief are interpreted as manifestations of the collective spin excitations in the system, the energy of which falls within a superconducting gap (spin exciton). The U-shaped divergent relief observed in the neutron scattering intensity is assigned to collective short-rage-order spin oscillations.