The mechanisms of the tunnel and multiphoton ionization transitions of hydrogen-like atoms and noble gas atoms are discussed. Atoms potassium and argon, with ionization energy of 4.34 and 15.76 eV, were chosen as the target. The atoms are exposed to Ti:Sapphire, (0,1)*LG, spiral amplitude modulated, laser beam at λ = 800 nm wavelength in a broad intensity range 1012 to 1015 W/cm2. The computational approach to describe tunnel and multiphoton processes was based on using the ADK theory. Stark and ponderomotive effects are also included to study their influence on the transition rate. Obtained results show that, for the lower γ values, the contribution of multiphoton ionization was less significant than the tunnel ionization contribution. In comparison, for higher γ values, multiphoton ionization dominated over tunnel ionization in a total transition rate. It is found that, in this particular case of spiral amplitude modulated mode, the intermediate regime, where both processes equally contribute, strongly depends on the atom selection and laser field intensity. Ionization in the intermediate regime occurs for γ ≈ 10 and 12 for low laser intensities, as γ ≈ 2 and 2.5 for the higher values, in the case of potassium and argon respectively. Our analysis indicated that the Stark and ponderomotive effects have a significant influence on the total transition rate. It is shown that these effects decrease the transition rate value and move the intermediate regime’s position toward lower values of the γ parameter, mainly in the case of higher laser field intensity.
Reply to the comment of P.L. Chapovsky to the paper “Symmetry approach in the problem of gas expansion into vacuum,” JETP 159, 794 (2021).
Silicon is indispensable in semiconductor industry. Understanding its high-temperature thermodynamic properties is essential both for theory and applications. However, first-principle description of high-temperature thermodynamic properties of silicon (thermal expansion coefficient and specific heat) is still incomplete. Strong deviation of its specific heat at high temperatures from the Dulong–Petit law suggests substantial contribution of anharmonicity effects. We demonstrate, that anharmonicity is mostly due to two transverse phonon modes, propagating in (111) and (100) directions, and can be quantitatively described with formation of the certain type of nanostructured planar defects of the crystal structure. Calculation of these defects' formation energy enabled us to determine their input into the specific heat and thermal expansion coefficient. This contribution turns out to be significantly greater than the one calculated in quasi-harmonic approximation.
The evolution of burning modes of a weak-current corona discharge in a diode filled with atmospheric air, having a pointed cathode and a flat anode, has been investigated. A theoretical description is performed in terms of an axisymmetric multifluid plasma model, including the kinetics of 9 types of particles and 25 plasma-chemical reactions. A discharge in a gap 10 mm long, with a needle-like cathode having a tip curvature radius of 100 μm, a source voltage of 8 kV, a ballast capacitance of 100 pF and a circuit ballast resistance of 1 MΩ, is described in detail. It is shown, both experimentally and theoretically, that the discharge has a lifetime of 180 μs and occurs in four clearly different stages under these conditions: (1) dark breakdown delay phase (0–20 μs); (2) Trichel pulse phase with a variable on–off time ratio and quasi-steady-state corona current component (20–80 μs); and (3) intermediate phase of monotonically rising weak current (80–130 μs), which ends with a vibrational transition to the (4) steady-state phase (130–180 μs), having a typical structure of glow discharge. The tendencies to a change in the corona discharge parameters with a variation in the feed voltage are analyzed. The results of theoretical calculations are in good agreement with the experimental data.
A theoretical method for evaluating the single-electron capture (SEC) cross sections in collisions of fast ions with a ground-state H 2 molecule is presented. The scattering problem for ion-molecule collisions is formulated in the impact parameter representation using the relation between the quantum-mechanical amplitude and quasi-classical impact parameter one. The capture amplitudes and corresponding probabilities of capture to ( nlm ) states of an incident ion are derived within the framework of the Brinkman–Kramers approximation. The general expressions for the SEC probability amplitudes to n -states, summed over l and m quantum numbers, are deduced, from which the corresponding SEC probabilities can be then calculated using a procedure of multichannel normalization. The dependence of the differential cross sections, integrated over projectile impact parameters, on the molecular orientation for charge exchange in H + + H 2 collisions is considered and compared with measurements and other calculations. Total SEC cross sections, integrated over the molecular orientations and summed over n -states for several bare and dressed ions, are calculated and compared with available experimental data and results of calculations by means of other theoretical methods.
We have constructed a theory of the Hall effect appearing during the passage of current in a magnetic tunnel junction due to the spin–orbit interaction in an insulator barrier in the approximation of a delta-shaped barrier potential. Both the normal Hall current flowing in metal banks as a result of asymmetric scattering in the tunneling barrier and the anomalous current existing only in the tunneling barrier due to the presence of the spin–orbit interaction in it are taken into account. We have considered the Rashba interaction that can be of intrinsic origin (noncentrosymmetric form of the barrier) or can be induced by an extraneous electric field emerging as a result of application of a potential difference to the barrier. Such a field can reach a value on the order of 10 9 W/m, which is close to intrinsic atomic fields. The Hall current has both linear and quadratic components in the voltage applied to the tunnel junction. The existence of the nonlinear Hall voltage corresponding to it has been illustrated experimentally in a CoFeB/MgO/Pt tunnel junction, in which the transverse (Hall) voltage has been measured in the Pt layer.
This paper is devoted to a theoretical study of the magnetic properties of an ensemble of single-domain interacting magnetic nanoparticles embedded in an immobile polymer matrix. This model is typical for the description of magnetically active polymer ferrocomposites widely used in industrial and biomedical applications. A ferrocomposite is assumed to be produced by carrier medium solidification in a ferrofluid in an external magnetic field h p at a polymerization temperature T p ; after carrier fluid solidification, the nanoparticles retain the spatial distribution and orientation of their easy magnetization axes that they had before carrier medium solidification. The contribution of interparticle dipole–dipole interactions to the static magnetization of a ferrocomposite as a function of the magnetic field strength h and polymerization field h p has been studied separately. The effects of the polymerization temperature and the size of magnetic nanoparticles on the magnetic properties of a ferrocomposite have been analyzed. The analytical expressions for the magnetization and initial magnetic susceptibility presented in the paper make it possible to predict the magnetic properties of a ferrocomposite as a function of its intrinsic characteristics and synthesis conditions, which is a theoretical basis for the production of ferrocomposites with a predetermined magnetic response in a given magnetic field.
Experimental investigations of antiferromagnetic topological insulator MnBi2Te4 have shown that the energy gap in samples may vary in a wide range. Since the energy gap is a key parameter of this system when used in developing new functional electronic devices, the reason for variation of the MnBi2Te4 energy gap at the Dirac point and its possible interrelation with magnetic interactions are matters of great importance and call for thorough analysis. To elucidate factors influencing the energy gap, we analyzed the variation of the electronic structure of the given topological insulator with surface van der Waals gap. Calculation data have shown that the energy gap at such structure modifications may vary in a wide range from 80–88 meV to 4–5 meV because of an intense spatial redistribution of topological surface states between septuple-layer MnBi2Te4 blocks with oppositely directed Mn magnetic moments. Our results suggest that the spatial localization of topological surface states is a primary factor governing the value of the energy gap, this localization being strongly dependent on structure modifications on the crystal surface.
We consider the Lifshitz topological transitions and the corresponding changes in the galvanomagnetic properties of a metal from the point of view of the general classification of open electron trajectories arising on Fermi surfaces of arbitrary complexity in the presence of magnetic field. The construction of such a classification is the content of the Novikov problem and is based on the division of non-closed electron trajectories into topologically regular and chaotic trajectories. The description of stable topologically regular trajectories gives a basis for a complete classification of non-closed trajectories on arbitrary Fermi surfaces and is connected with special topological structures on these surfaces. Using this description, we describe here the distinctive features of possible changes in the picture of electron trajectories during the Lifshitz transitions, as well as changes in the conductivity behavior in the presence of a strong magnetic field. As it turns out, the use of such an approach makes it possible to describe not only the changes associated with stable electron trajectories, but also the most general changes of the conductivity diagram in strong magnetic fields.
We present comparative theoretical investigation of thermoelectric power and Hall effect in the Hubbard model for correlated metal and Mott insulator (considered as prototype cuprate superconductor) for different concentrations of current carriers. Analysis is performed within standard DMFT approximation. For Mott insulator we consider the typical case of partial filling of the lower Hubbard band (hole doping). We calculate the dependence of thermopower on doping level and determine the critical concentration of carriers corresponding to sign change of thermopower. An anomalous dependence of thermopower on temperature is obtained significantly different from linear temperature dependence typical for the usual metals. The role of disorder scattering is analyzed on qualitative level. The comparison with similar studies of the Hall effect shows, that breaking of electron - hole symmetry leads to the appearance of the relatively large interval of band - fillings (close to the half - filling) where thermopower and Hall effects have different signs. We propose a certain scheme allowing to determine the number of carriers from ARPES data and perform semi - quantitative estimate of both thermopower and Hall coefficient using the usual DFT calculations of electronic spectrum.
Films of metal-insulator nanogranular composites M x D 100 – x with different composition and percentage of metal and dielectric phases (M = Fe, Co, CoFeB; D = Al 2 O 3 , SiO 2 , LiNbO 3 ; x ≈ 15–70 at %) are investigated by magnetic resonance in a wide range of frequencies ( f = 7–37 GHz) and temperatures ( T = 4.2–360 K). In addition to the usual ferromagnetic resonance signal from an array of nanogranules, the experimental spectra contain an additional absorption peak, which we associate with the electron paramagnetic resonance (EPR) of Fe and Co ions dispersed in the insulating space between the granules. In contrast to the traditional EPR of Fe and Co ions in weakly doped non-magnetic matrices, the observed peak demonstrates a number of unusual properties, which we explain by the presence of magnetic interactions between ions and granules.
We investigate fluctuations of vorticity inside a coherent vortex generated by the inverse energy cascade in two-dimensional turbulence. Temporal and spatial correlations can be characterized by the pair correlation function. The interaction of fluctuations leads to a nonzero third moment of vorticity. We analyze the pair correlation function and the third moment using a model in which the pumping is short-correlated in time and derive explicit expressions for the Gaussian spatial correlation function for the pumping force.
An Erratum to this paper has been published: https://doi.org/10.1134/S1063776123110171
The behavior of fine-grained YBa 2 Cu 3 O 6.92 HTSCs during cooling in a weak magnetic field is investigated. The magnetization of samples, the crystallite sizes is which are comparable with the magnetic field penetration depth, is comprehensively analyzed in the range below the superconducting transition temperature. When the crystallite size is smaller than 0.5 μm, vortices are shown not to be fixed to pinning centers, and the temperature dependence of magnetization is completely determined by the screening of crystallites and the temperature of appearance of intercrystallite superconducting currents.
The multiphoton excitation and high harmonic generation (HHG) processes are considered using the microscopic quantum theory of nonlinear interaction of strong coherent electromagnetic (EM) radiation with rectangular graphene quantum dot (GQD) with zigzag edges and more than 80 atoms. The dynamic Hartree–Fock approximation has been used to consider the quantum dot-laser field nonlinear interaction at the nonadiabatic multiphoton excitation regime. The many-body Coulomb interaction is described in the extended Hubbard approximation. By numerical results, we show the significance of the rectangular GQD lateral size, shape, and EM wavefield orientation in rectangular GQD of the zigzag edge in the HHG process allowing for increasing the cutoff photon energy and the quantum yield of higher harmonics.
Using the successively inverted projection method, we studied the dynamics of ultralean hydrogen–air flames propagating freely in a horizontal cylindrical Hele–Shaw cell. To quantify the two revealed characteristics of the flame dynamics—the dependence of the average flame velocities on time and the dependence of the initial flame velocity on the stoichiometry of the initial hydrogen–air mixture—we proposed time and stoichiometric scaling relations. The first relation approximates the dependence of the path of the flame front in hydrogen–air mixtures with an initial hydrogen concentration exceeding a certain critical value. The second relation approximates the dependencies of the initial flame front velocities on the hydrogen concentration. The general relationships for topologically different types of ultralean hydrogen–air flames can be interpreted as additional evidence of the presence of a general mechanism for the transition from discrete fronts of isolated drifting ball flames to a quasi-continuous deflagration flame front through a cascade of bifurcations.
A new method is proposed for determining level splitting Δ in a double-well 1D potential. Two “partner” functions (one symmetric Ψ+ and the other antisymmetric Ψ–) are determined. From these functions, potentials V+(x) and V–(x) and energies E_ + ^0 and E_ - ^1 corresponding to them are determined from the Schrödinger equation. A unique property of Ψ+ and Ψ– is identity E_ + ^0 = E_ - ^1 , which makes it possible to determine Δ from the perturbation theory in parameter V+(x) – V–(x). For a double-well oscillator potential, the expression for the level splitting, which connects the instanton and single-well limits, is obtained. These results can be employed in the field theory, for which the possibility of obtaining instanton solutions from perturbation theory has been discussed more than once. A number of potentials are considered, for which the value of Δ can be determined without using the semiclassical approximation. Singular potentials of the funnel type are analyzed. The value of Δ determined in this study is compared with the results of numerical solution of the Schrödinger equation for the instanton potential.
The second harmonic radiation of a single-pass free electron laser (FEL) and its dependence on the second harmonic of the undulator field are investigated. In analysis of properties of materials, the nonlinear generation of the second harmonic as a response to radiation is an important effect. In this context, the second harmonic generation of the radiation source (FEL) is undesirable since it masks the signal being analyzed. Conversely, in other cases, the second harmonic radiation of the FEL can be useful as radiation with a higher frequency. We investigate the possibility of suppression (or, conversely, enhancement) of the FEL second harmonic power depending on the phase and strength of the second harmonic of the FEL undulator field. The proposed approach is independent in principle of the radiation frequency. We consider examples of LCLS and PAL-XFEL in the X-ray range and SPARC and LEUTL in the visible range. The more effective influence of the undulator field harmonic in operation with narrow electron beams is demonstrated.
The influence of substitutional impurities on adhesion at the TiAl/Al 2 O 3 interface with an oxygen termination has been studied by the projector augmented-wave method within the density functional theory. It has been shown that transition metals and a number of s , p -elements substituting for the interfacial titanium atom reduce adhesion, whereas Group VB and VIB elements enhance chemical bonding at the interface. The local densities of states, charge density distribution, overlap populations for interfacial atom bonding, and other electronic characteristics have been calculated that make it possible to reveal key factors influencing adhesion at the alloy–oxide interface. A correlation has been found between the influence of impurities on bonding energy at the inner and outer interfaces. A comparison of obtained data with those for the interface with Ti-enriched Ti 3 Al alloy shows that the interface loses strength with decreasing Ti content in the alloy.
