Amplitude Of External Field Research Articles

Gauge dependence in QED amplitudes in expanding de Sitter space

We consider first-order transition amplitudes in external fields in QED in the expanding de Sitter space and point out that they are gauge dependent quantities. We examine the gauge variations of the amplitudes assuming a decoupling of the interaction at large times, which allows to conclude that the source of the problem lies in the fact that the frequencies of the modes in the infinite future become independent of the comoving momenta. We show that a possibility to assure the gauge invariance of the external field amplitudes is to restrict to potentials which vanish sufficiently fast at infinite times, and briefly discuss a number of options in the face of the possible gauge invariance violation in the full interacting theory.

Magnetization Processes Study in the Implanted Garnet Films Using the Second-Harmonic Generation Effect

In the work, magnetization-induced second-harmonic generation (MSHG) effect has been appliedto investigate the magnetization distribution changes, induced by ion implantation into thethin surface layer of garnet film.The studies were performed on the (111)-orientedepitaxial garnet film (YSmLuCa)$_3$(FeGa)$_5$O$_{12}$ implanted with $1.5\times10^{16}$~cm$^{-2}$dose of H$_2^+$ ions at $60$~keV energy. The measurements of the MSHG effectwere performed as a function of amplitude of perpendicular external magnetic field. The observed complex field dependencesof the remagnetization processes for the implanted garnet film studied were described in theframe of a phenomenological model developed. The model of the MSHG effect allows to performdecomposition of measured dependences on separate contributions originating from magnetizationcomponents related to implanted and unimplanted film volumes.

Wave propagation in the presence of a dielectric slab: The paraxial approximation

Light propagation processes in a homogeneous dielectric slab are considered from the point of view of the optical analog of the Schrödinger equation. The reflection and transmission coefficients and longitudinal shifts of the wavefront are determined by considering the analytical properties of the external field amplitudes as functions of the wave number. An analytic approach to obtain the resonances in the “long lifetime” limit is also presented.

Nonequilibrium dynamics of a mixed spin-1/2 and spin-3/2 Ising ferrimagnetic system with a time dependent oscillating magnetic field source

Nonequilibrium phase transition properties of a mixed Ising ferrimagnetic model consisting of spin-1/2 and spin-3/2 on a square lattice under the existence of a time dependent oscillating magnetic field have been investigated by making use of Monte Carlo simulations with a single-spin flip Metropolis algorithm. A complete picture of dynamic phase boundary and magnetization profiles have been illustrated and the conditions of a dynamic compensation behavior have been discussed in detail. According to our simulation results, the considered system does not point out a dynamic compensation behavior, when it only includes the nearest-neighbor interaction, single-ion anisotropy and an oscillating magnetic field source. As the next-nearest-neighbor interaction between the spins-1/2 takes into account and exceeds a characteristic value which sensitively depends upon values of single-ion anisotropy and only of amplitude of external magnetic field, a dynamic compensation behavior occurs in the system. Finally, it is reported that it has not been found any evidence of dynamically first-order phase transition between dynamically ordered and disordered phases, which conflicts with the recently published molecular field investigation, for a wide range of selected system parameters.

Kink model of state switching in quasi-one-dimensional nanosystems

A method for the analytical calculation of the kinetics of state switching induced by external field in quasi-one-dimensional systems has been developed. This method is based on the Kolmogorov approach, which was proposed to describe statistical crystallization. As applied to magnetic systems, it allows one to cal- culate magnetization curves and hysteresis loops. The results of analytical calculation are confirmed by sto- chastic Monte Carlo simulation, which also makes it possible to find characteristics of mixed domain states formed as a result of the multiple cycling of the external field amplitude.

Electron transport through a two-terminal Aharonov-Bohm interferometer coupled with linear di-quantum dot molecules

A two-terminal Aharonov-Bohm (A-B) interferometer coupled with linear di-quantum dot molecules is presented. By employing Keldysh non-equilibrium Green's function technique, the conductance without introducing time-dependent external field and the average current with applying time-dependent external field are theoretically studied. In the absence of time-dependent external field, two identical linear diquantum dot molecules embedded respectively in the two arms of A-B interferometer lead to degeneracy energy levels. The central resonance peak at εd = 0 in the conductance spectrum splits into two resonance peaks as the inter-coupling strength of di-quamtum dot increases over a threshold. In the case that the two linear di-quantum dot molecules are different, three or four resonance peaks appear in the conductance spectrum. When tuning magnetic flux ψ= π, the destructive quantum interference of electron waves in the A-B interferometer takes place. The conversion between 0 and 1 for conductance is performed by switching on/off the magnetic flux, which suggests a new physical scheme of quantum switches. The effect of Rashba spin-orbit interaction on the conductance is discussed. The functionality of spin filter is suggested through adjusting the Rashba spin-orbit coupling strength and the external magnetic flux. When time-dependent external field is applied, the notable side-band effect appears in the average current curve. A series of resonance peaks is produced, with the peak-peak separation of ħω. Two main peaks become reduced as the amplitude of time-dependent external field increases, however, the sideband peaks grow gradually. This indicates that both the magnitude and the position of average current resonance peak are controllable by adjusting the amplitude of time-dependent external field. The sideband effect remains always in the average current curve no matter how much the frequency of time-dependent external field changes. But the increase in the frequency of external field leads to the growth of two main peaks at the bonding and anti-bonding energy respectively, and the decay of the corresponding sideband peaks as well. The conversion between the current peak and valley can be realized by tuning the frequency of time-dependent field. Moreover, the dependence of A-B effect of the average current on the magnetic flux is found. As the magnetic flux is ψ≠nπ, each peak in average current curves splits into two peaks. But under the condition of ψ=2nπ, the splitting phenomenon disappears. The spin-dependent average current shows effective controllability by tuning the magnetic flux and Rashba spin-orbit coupling. The results would be useful for gaining a physical insight into electron transport in the multi-quantum-dot molecules coupled A-B interferometer and for designing the quantum devices.

Normal and inverse magnetocaloric effect in magnetic multilayers with antiferromagnetic interlayer coupling

The thermodynamics of a spin-1/2 magnetic multilayer system with antiferromagnetic interplanar couplings is studied using the pair approximation method. Special attention is paid to magnetocaloric properties, quantified by isothermal entropy change. The multilayer consists of two kinds of magnetic planes, one of which is diluted. The intraplanar couplings in both planes have arbitrary anisotropy ranging between Ising and isotropic Heisenberg interactions. The phase diagram related to the occurrence of magnetic compensation phenomenon is constructed and discussed. Then the isothermal entropy change is discussed as a function of interaction parameters, magnetic component concentration and external magnetic field amplitude. The ranges of normal and inverse magnetocaloric effect are found and related to the presence or absence of compensation.

Multiferroic and magnetoelectric properties of La0.1Ba0.9Fe12O19 ceramics

La0.1Ba0.9Fe12O19 powders with similar hexagonal crystal structure to BaFe12O19 have been successfully synthesized using polymer precursor method. The powders were suppressed into pellets, which were sintered into ceramics at 1,300 °C for 1 h. The structure and morphology of the ceramics have been determined by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Clear electric hysteresis loops upon different amplitude of external fields indicates that La0.1Ba0.9Fe12O19 is a kind of possible ferroelectric compound. The maximum remnant polarization of La0.1Ba0.9Fe12O19 ceramic is estimated to be ~9.6 μC/cm2. The FeO6 octahedron in its perovskite-like hexagonal unit cell as well as the shift of Fe3+ off the center of octahedron are proposed to be the origin of electric polarization in La0.1Ba0.9Fe12O19. Simultaneous occurrence of large ferroelectricity and strong ferromagnetism has been observed in La0.1Ba0.9Fe12O19 ceramics. More interestingly, this compound demonstrates electronic polarization behavior being actuated by an applied magnetic field, indicating the existence of magnetoelectric (ME) coupling effect in the La0.1Ba0.9Fe12O19 ceramics. Our results may lead to new device applications such as magnetically recorded ferroelectric memory.

Abnormal surface diffusion of particles under the action of an external time-periodic force

This paper delves into the abnormal surface diffusion of particles in an external time-periodic field. The relationship is studied of the surface diffusion enhancement as a function of the amplitude and frequency of external fields. It is shown that the diffusion coefficient can be significantly increased (by several orders of magnitude) by applying external time-periodic fields. The diffusion gain ratio stronglly depends on the surface temperature and on the external field amplitude and frequency.

Collective modes in free plasmas subjected to a radiation field

In this study we report the effects of an electromagnetic field on the physical properties of free plasmas3.The calculations are carried out in the semi-classical approximation, i.e., the electromagnetic field is treated classically and the electrons from a quantum mechanical viewpoint. The results show that the collective modes are damped away more smoothly and in a smaller frequency range than those reported by previous studies. An exponential-like decay of the frequencies is readily observable from the plot of the plasmon frequency as a function of the external field amplitude. We successfully recreate the results of previous studies. We also obtain that the single photon processes has a pronounced effect on the decrease of the frequency range of modulation.

One type of three-wave interaction of low-frequency waves in magnetoactive plasma of the solar atmosphere

We study the process of occurrence of “quasi-mode” decay instability of kinetic Alfven waves (KAW) in the chromosphere of a solar active region before a flare, namely, in plasma of magnetic loops near their footpoints. The decay of a primary KAW into a kinetic ion-acoustic wave and a secondary KAW was considered as a specific type of three-wave interaction. Necessary conditions for the KAW decay instability occurrence were found for two semiempirical models of the solar atmosphere with the use of a modified expression for the growth rate of instability in the case of nonlinear interaction of low-frequency waves with an abnormally low excitation threshold. It was shown that the main criteria for the development of this instability significantly depend on the amplitude of external magnetic field in the region under study as well as on a model of the solar atmosphere.

Critical phenomena in dynamical Ising-typed thin films by effective-field theory

The stationary state solutions of the Ising-typed thin films with different layers in the presence of an external oscillatory field are examined within the effective-field theory. The study focuses on the effects of external field frequency and amplitude on the overall behavior. Particular attention is paid on evolution of the special point with dynamic field frequency corresponding to critical temperature of the three-dimensional infinite bulk system where the surface and modified exchange parameters are of no importance. Some findings such as surface enhancement phenomenon and effect of thickness on the dynamic process are introduced together with some other well known characteristics. An attempt is made to explain the relations between the competing time scales (intrinsic microscopic relaxation time of the system and the time period of the external oscillatory field) and frequency dispersion of the critical temperature coordinate of the special point.

Monte Carlo simulation of spin relaxation of conduction electrons in silicon

Recently, electrical injection of spin polarization in n-type and p-type silicon up to room-temperature has been experimentally carried out. Despite of these promising experimental results, a comprehensive theoretical framework concerning the influence of transport conditions on the spin depolarization process in silicon structures, in a wide range of values of temperature, doping concentration and amplitude of external fields, is still in a developing stage. In this contribution we use a semiclassical multiparticle Monte Carlo approach to simulate the electron transport and spin dynamics in lightly doped n-type Si crystals and numerically calculate the spin lifetimes of drifting electrons. Spin flipping is taken into account through the Elliot-Yafet mechanism, which is dominant in group IV materials. We discuss the influence of different intravalley and intervalley phonon interactions in the spin relaxation process during the spin transport. Our findings are in good agreement with those obtained by using different theoretical approaches. Moreover, our Monte Carlo predictions, in ranges of temperature and field amplitude yet unexplored, can guide future experimental studies towards a more effective design of room-temperature silicon based spintronic-devices.

Monte Carlo simulation of spin relaxation of conduction electrons in silicon

Recently, electrical injection of spin polarization in n-type and p-type silicon up to room-temperature has been experimentally carried out. Despite of these promising experimental results, a comprehensive theoretical framework concerning the influence of transport conditions on the spin depolarization process in silicon structures, in a wide range of values of temperature, doping concentration and amplitude of external fields, is still in a developing stage. In this contribution we use a semiclassical multiparticle Monte Carlo approach to simulate the electron transport and spin dynamics in lightly doped n-type Si crystals and numerically calculate the spin lifetimes of drifting electrons. Spin flipping is taken into account through the Elliot-Yafet mechanism, which is dominant in group IV materials. We discuss the influence of different intravalley and intervalley phonon interactions in the spin relaxation process during the spin transport. Our findings are in good agreement with those obtained by using different theoretical approaches. Moreover, our Monte Carlo predictions, in ranges of temperature and field amplitude yet unexplored, can guide future experimental studies towards a more effective design of room-temperature silicon based spintronic-devices.

Off-resonance energy absorption in a linear Paul trap due to mass selective resonant quenching

Linear Paul traps (LPT) are used in many experimental studies such as mass spectrometry, atom-ion collisions, and ion-molecule reactions. Mass selective resonant quenching (MSRQ) is implemented in LPT either to identify a charged particle's mass or to remove unwanted ions from a controlled experimental environment. In the latter case, MSRQ can introduce undesired heating to co-trapped ions of different mass, whose secular motion is off resonance with the quenching ac field, which we call off-resonance energy absorption (OREA). We present simulations and experimental evidence that show that the OREA increases exponentially with the number of ions loaded into the trap and with the amplitude of the off-resonance external ac field.

Micro-/macro-responses of a ferroelectric single crystal with domain pinning and depinning by dislocations

Phase field simulations are conducted to investigate the micro-structural signature and the macro-response of a ferroelectric single crystal with domain pinning and depinning phenomena by dislocation arrays. It is shown that due to the presence of the dislocation arrays, a domain with polarizations antiparallel to an applied field can survive under the small amplitude of applied field. The residual domain serves as a pre-existing nucleus during the following macroscopic switching via only domain wall motion. The pinned domain will be depinned when the external electric field amplitude exceeds a critical value, which highly depends on the dislocation spacing in the dislocation array. Due to the pinning and depinning effect, an asymmetric hysteresis loop of polarization versus electric field might appear when a bias field is applied.

Low-frequency polarization relaxation in PMN + 2% Li2O ferroelectric ceramics in the region of diffuse phase transition

Studies of dielectric nonlinearity in lead magnoniobate ceramics doped with lithium show that at a certain value of external field amplitude E, two peaks appear on the temperature dependences of effective dielectric permittivity ɛeff′(T). They are caused by the dynamics of the polar regions in the vicinity of diffuse phase transition and by variation in their volume under the action of field E.

Linear and nonlinear density response functions for a simple atomic fluid

We use molecular dynamics simulations to investigate the linear and nonlinear density response functions for simple fluids under the influence of spatially periodic external fields. Using a direct Fourier space decomposition of the instantaneous microscopic density for the perturbed fluid we can clearly identify the distinct order of response. Using a single component sinusoidal longitudinal force for a set of wavelengths and amplitudes we show that in the linear response regime the proportionality between the external field amplitude and the density perturbation can be used to determine the linear density response function, and hence the pair correlation function, static liquid structure factor, and lowest order direct correlation function. We show also that for large external field amplitudes a single component external field can be used to determine the form for lowest order and second lowest order nonlinear response functions for restricted regions of the total response function spaces.

Stress relaxation in polycarbonates

A procedure is presented for investigation of stress relaxation in various brands of foreign and domestic polycarbonates in different stages of loading. This study is the first to cite results of experimental investigations of stress relaxation in carbonates subject to long-term tests at a constant strain rate. The results are then processed statistically, and stress‐relaxation curves are constructed, and the latter analyzed and mathematically described. Model representation of stress relaxation in polycarbonates has made it possible to determine the time required for stress relaxation. In addition to such basic advantages as high resistance to aggressive media, atmospheric effects, etc., polymeric materials possess a number of disadvantages: low heat stability and thermal resistance, and tendency to creep and stress relaxation. Relaxation is a physical process whereby a system goes over into an equilibrium state, and is sufficient to have altered external energy conditions. As applies to polymeric materials, the rate of relaxation and its intensity will depend on their chemical and physical structure, intermolecular interaction, and parameters of the external energy field (temperature, mechanical stress, amplitude and frequency of loading, etc.). Stress relaxation during constant deformation is described,

Spaser operation in the presence of external optical field

The operation of surface plasmon amplifier by stimulated emission of radiation (spaser) in the presence of external optical field is analyzed. The range of external field amplitude E and mismatch Δ of the external field frequency and the spaser generation frequency (Arnold tongue) E > Esynchr(Δ) in which the spaser works at the external field frequency is determined. The analytical and numerical calculations at the given mismatch Δ yield three ranges: E EL (the spaser generation is suppressed and the spaser polarization is equal to the polarization of nanoparticle in the presence of external field).