External Field Configuration Research Articles

Strain-induced multi-band spin-wave logic gate based on alligator-type magnonic crystal/PZT structure

Here, we report the results of strain-controlled spin-wave propagation regimes in a double-period multiferroic structure. It consists of an alligator-type magnonic crystal with a period of 250 μm and a piezoelectric layer, featuring a periodic counter-pin-type electrode system with a period of 125 μm. Employing microwave measurements, we acquired the transmission and dispersion of spin waves under various external electric field configurations applied to the piezoelectric layer. The formation of bandgaps in the magnon spectrum and the variation of the spin-wave transmission when altering the configurations of the external electric field are demonstrated. A finite element method reveals that the combination of the non-uniformity in the initial internal magnetic field of the magnonic crystal, which is caused by the presence of periodic alligator-type regions, together with elastic deformations, heightens the amplitude of the modulation of the internal magnetic field. Micromagnetic modeling has demonstrated that this modulation enhancement results in the variation of the spin-wave transmission at the frequency of the magnonic bandgap center of the magnonic crystal. The proposed design of the reconfigurable magnonic crystal creates a condition for the nucleation of the spin-wave bandgap, with further enhancement of the spin-wave reflection from the periodic grating induced by strain. We demonstrate the potential use of the proposed device as a multi-band NAND/NXOR spin-wave based logic gate.

Optically polarized selective transmission of a fractional vector vortex beam by the polarized atoms with external magnetic fields.

We investigate the role of external magnetic fields and linearly polarized pump light, especially when their directions are parallel or vertical, on the propagation of the fractional vector vortex beams (FVVBs) through a polarized atomic system. Herein, the different configurations of external magnetic fields lead to various optically polarized selective transmissions of FVVBs with different fractional topological charge α caused by the polarized atoms, which is theoretically demonstrated by the atomic density matrix visualization analysis and experimentally explored by Cesium atom vapor. Meanwhile, we find that the FVVBs-atom interaction is a vectorial process due to the different optical vector polarized states. In this interaction process, the atomic optically polarized selection property provides potential for the realization of the magnetic compass based on warm atoms. For the FVVBs, due to the rotational asymmetry of the intensity distribution, we can observe some transmitted light spots with unequal energy. Compared with the integer vector vortex beam, it is possible to obtain a more precise magnetic field direction by fitting the different "petal" spots of the FVVBs.

Effect of external electromagnetic field configuration on metal structure of welded joints of structural steel

The Paton Welding Journal, 2022, №10. International Scientific-Technical and Production Journal «The Paton Welding Journal» «The Paton Welding Journal» has been published monthly since 2000 in English, ISSN 0957-798X. «The Paton Welding Journal» is a cover-to-cover English translation of the «Avtomaticheskaya Svarka» (Automatic Welding) journal. The «Avtomaticheskaya Svarka» journal has been published monthly since 1948 in Russian, ISSN 005-111X.

Charged and rotating multi-black holes in an external gravitational field

We construct analytical and regular solutions in four-dimensional General Relativity which represent multi-black hole systems immersed in external gravitational field configurations. The external field background is composed by an infinite multipolar expansion, which allows to regularise the conical singularities of an array of collinear static black holes. A stationary rotating generalisation is achieved by adding independent angular momenta and NUT parameters to each source of the binary configuration. Moreover, a charged extension of the binary black hole system at equilibrium is generated. Finally, we show that the binary Majumdar–Papapetrou solution is consistently recovered in the vanishing external field limit. All of these solutions reach an equilibrium state due to the external gravitational field only, avoiding in this way the presence of any string or strut defect.

Dynamics of a fermion with dipole moments in external wave fields

We discuss the motion of a massive fermion spin 1/2 particle in external wave field configurations when the Pauli type non-minimal interaction of the gauge field strengths with particle’s dipole moments is taken into account. The exact solution of the relativistic Dirac-Pauli equation is presented for the case of the plane electromagnetic wave.

EXACT ANALYTICAL AND APPROXIMATE ASYMPTOTIC CALCULATION METHODS TO DETERMINE THREE-DIMENSIONAL ELECTROMAGNETIC FIELD NEAR CONDUCTING BODY WITH FLAT SURFACE

The analytical solution of the three-dimensional quasi-stationary electromagnetic field problem for a current located near conducting body with a flat surface is considered. The exact and approximate solution of the problem is presented. The exact solution has no restrictions on the external field configuration, physical properties of the medium, and frequency. The approximate solution is based on an expansion in asymptotic series and has limitations: for sinusoidal field, the solution is limited to frequencies above the lower limit; for pulsed field, the solution is limited by the initial time interval of the current pulse. Based on comparison of the results of exact and approximate calculations for nonuniform sinusoidal field at the interface between the media, the admissible value of the introduced small parameter is determined. For pulsed field the proposed choice of the limited time interval for calculating electomagnetic field using the asymptotic method is justified. References 29, figures 7.

Observation of mode splitting in artificial spin ice: A comparative ferromagnetic resonance and Brillouin light scattering study

We report the dependence of the magnetization dynamics in a square artificial spin-ice lattice on the in-plane magnetic field angle. Using two complementary measurement techniques—broadband ferromagnetic resonance and micro-focused Brillouin light scattering spectroscopy—we systematically study the evolution of the lattice dynamics, for both a coherent radio frequency excitation and an incoherent thermal excitation of spin dynamics. We observe a splitting of modes facilitated by inter-element interactions that can be controlled by the external field angle and magnitude. Detailed time-dependent micromagnetic simulations reveal that the split modes are localized in different regions of the square network. This observation suggests that it is possible to disentangle modes with different spatial profiles by tuning the external field configuration.

Generation of oblique electromagnetic wave by hot injection electron beam with parallel AC electric field in the magnetosphere of Saturn

The Cassini radio and plasma wave investigation is designed to study radio emissions, plasma waves, thermal plasma, and dust in the vicinity of Saturn. Plasma particles, waves and fields are the major factors on which present knowledge about Saturn’s magnetosphere is based from the three flyby missions. For the present work, our examination is focused to study those waves who have frequency lower than electron cyclotron frequency in Saturnian magnetosphere. In this paper, we investigate the growth rate of whistler mode waves in magneto-plasma of Saturn. A dispersion relation for parallel propagating whistler mode waves has been applied to the magnetosphere of Saturn. The effect of electron density, temperature anisotropy, number density and A.C frequency on the temporal growth rate of the whistler mode emission is studied. For the given magnetic field and external electric field configuration, the general dispersion relation has been derived.

Bosonic pair creation and the Schiff-Snyder-Weinberg effect

Interactions between different bound states in bosonic systems can lead to pair creation. We study this process in detail by solving the Klein-Gordon equation on space-time grids in the framework of time-dependent quantum field theory. By choosing specific external field configurations, two bound states can become pseudodegenerate, which is commonly referred to as the Schiff-Snyder-Weinberg effect. These pseudodegenerate bound states, which have complex energy eigenvalues, are related to the pseudo-Hermiticity of the Klein-Gordon Hamiltonian. In this work, the influence of the Schiff-Snyder-Weinberg effect on pair production is studied. A generalized Schiff-Snyder-Weinberg effect, where several pairs of pseudodegenerate states appear, is found in combined electric and magnetic fields. The generalized Schiff-Snyder-Weinberg effect likewise triggers pair creation. The particle number in these situations obeys an exponential growth law in time enhancing the creation of bosons, which cannot be found in fermionic systems.

Time-dependent pair creation and the Schwinger mechanism in graphene

The momentum spectrum of positively and negatively charged carriers created in intrinsic graphene submitted to a time-dependent external electric field is evaluated for many external field configurations. Owing to the formal analogy between relativistic quantum mechanics and the description of graphene quasiparticles in terms of the massless Dirac equation, the electron momentum density is evaluated within two-dimensional massless quantum electrodynamics coupled to a strong classical field. This allows the treatment of dynamical effects in electron-hole creation and gives a physical description in terms of the time-dependent Schwinger mechanism. At zero transverse momentum, it is shown that the Fermi bound in the electron-hole momentum spectrum is saturated in a certain momentum window and the pair density depends only on the potential difference between asymptotic potentials before and after the interaction. The pair density for nonzero transverse momenta is evaluated using numerical calculations. The numerical results demonstrate that an important number of pairs can be created by an external field through both tunneling and multiphoton processes. It is argued that these features of the dynamical pair production may facilitate the detection of the Schwinger mechanism using graphene as a condensed matter analog to quantum electrodynamics.

Floquet-Bloch theory and topology in periodically driven lattices.

We propose a general framework to solve tight binding models in D dimensional lattices driven by ac electric fields. Our method is valid for arbitrary driving regimes and allows us to obtain effective Hamiltonians for different external field configurations. We establish an equivalence with time-independent lattices in D+1 dimensions and analyze their topological properties. Furthermore, we demonstrate that nonadiabaticity drives a transition from topological invariants defined in D+1 to D dimensions. Our results have potential applications in topological states of matter and nonadiabatic topological quantum computation, predicting novel outcomes for future experiments.

An ansatz for the nonlinear Demkov-Kunike problem for cold molecule formation

We study nonlinear mean-field dynamics of ultracold molecule formation in the case when the external field configuration is defined by the level-crossing Demkov-Kunike model, characterized by a bell-shaped coupling and finite variation of the detuning. Analyzing the fast sweep rate regime of the strong interaction limit, which models a situation when the peak value of the coupling is large enough and the resonance crossing is sufficiently fast, we construct a highly accurate ansatz to describe the temporal dynamics of the molecule formation in the mentioned interaction regime. The absolute error of the constructed approximation is less than 3 × 10−6 for the final transition probability while at certain time points it might increase up to 10−3. Examining the role of the different terms in the constructed approximation, we prove that in the fast sweep rate regime of the strong interaction limit the temporal dynamics of the atom-molecule conversion effectively consists of the process of resonance crossing, which is governed by a nonlinear equation, followed by atom-molecular coherent oscillations which are basically described by a solution of the linear problem, associated with the considered nonlinear one.

Demkov-kunike model for cold atom association: Weak interaction regime

We study the nonlinear mean-field dynamics of molecule formation at coherent photo- and magneto-association of an atomic Bose-Einstein condensate for the case when the external field configuration is defined by the quasi-linear level crossing Demkov-Kunike model, characterized by a bell-shaped pulse and finite variation of the detuning. We present a general approach to construct an approximation describing the temporal dynamics of the molecule formation in the weak interaction regime and apply the developed method to the nonlinear Demkov-Kunike problem. The presented approximation, written as a scaled solution to the linear problem associated to the nonlinear one we treat, contains fitting parameters which are determined through a variational procedure. Assuming that the parameters involved in the solution of the linear problem are not modified, we suggest an analytical expression for the scaling parameter.

Two strong nonlinearity regimes in cold molecule formation

Two distinct strongly non-linear scenarios of molecule formation in an atomic Bose-Einstein condensate (either by photoassociation or Feshbach resonance) corresponding to large and small field detuning are revealed. By examining arbitrary external field configurations, we show that the association process in the first case is almost non-oscillatory in time while in the second case the evolution of the system displays strongly pronounced Rabi-type oscillations. We construct highly accurate approximate solutions for both limit cases. We show that at strong coupling limit the non-crossing models are able to provide conversion of no more than one third of the initial atomic population. Finally, we show that for constant-amplitude models involving a finite final detuning the strong interaction limit is not optimal for molecule formation.

Full configuration interaction approach to the few-electron problem in artificial atoms

We present a new high performance configuration interaction code optimally designed for the calculation of the lowest-energy eigenstates of a few electrons in semiconductor quantum dots (also called artificial atoms) in the strong interaction regime. The implementation relies on a single-particle representation, but it is independent of the choice of the single-particle basis and, therefore, of the details of the device and configuration of external fields. Assuming no truncation of the Fock space of Slater determinants generated from the chosen single-particle basis, the code may tackle regimes where Coulomb interaction very effectively mixes many determinants. Typical strongly correlated systems lead to very large diagonalization problems; in our implementation, the secular equation is reduced to its minimal rank by exploiting the symmetry of the effective-mass interacting Hamiltonian, including square total spin. The resulting Hamiltonian is diagonalized via parallel implementation of the Lanczos algorithm. The code gives access to both wave functions and energies of first excited states. Excellent code scalability in a parallel environment is demonstrated; accuracy is tested for the case of up to eight electrons confined in a two-dimensional harmonic trap as the density is progressively diluted up to the Wigner regime, where correlations become dominant. Comparison with previous quantum Monte Carlo simulations in the Wigner regime demonstrates power and flexibility of the method.

Entanglement in Anisotropic Heisenberg Model with Non-UniformExternal Fields

We study entanglement properties of the three-qubit anisotropic Heisenbergmodel with both uniform and non-uniform external magnetic fields.Analytic expressions for the measures of entanglement at theground state are obtained. We show that the pairwise entanglementand global entanglement of the system at the ground state clearlydepend on the strength and configuration of external fields. Theentanglement between some pairs can be enhanced by non-uniformexternal fields.

POINT PARTICLE–SYMMETRIC TENSORS INTERACTION AND GENERALIZED GAUGE PRINCIPLE

The model of a point particle in the background of external symmetric tensor fields is analyzed from the higher spin theory perspective. It is proposed that the gauge transformations of the infinite collection of symmetric tensor fields may be read off from the covariance properties of the point particle action w.r.t. general canonical transformations. The gauge group turns out to be a semidirect product of all phase space canonical transformations to an Abelian ideal of "hyperWeyl" transformations and includes U(1) and general coordinate symmetries as a subgroup. A general configuration of external fields includes rank-0,1,2 symmetric tensors, so the whole system may be truncated to ordinary particle in Einstein–Maxwell backgrounds by switching off the higher-rank symmetric tensors. When otherwise all the higher rank tensors are switched on, the full gauge group provides a huge gauge symmetry acting on the whole infinite collection of symmetric tensors. We analyze this gauge symmetry and show that the symmetric tensors which couple to the point particle should not be interpreted as Fronsdal gauge fields, but rather as gauge fields of some conformal higher spin theories. It is shown that the Fronsdal fields system possesses twice as many symmetric tensor fields as is contained in the general background of the point particle. Besides, the particle action in general backgrounds is shown to reproduce De Wit–Freedman point particle–symmetric tensors first order interaction suggested many years ago, and extends their result to all orders in interaction, while the generalized equivalence principle completes the first order covariance transformations found in their paper, in all orders.

On the influence of strong electric and magnetic fields on spatial dispersion and anisotropy of the optical properties of a semiconductor

Nonperturbative methods were used to construct a single-integral equation for the photon polarization operator in a semiconductor in strong electric and magnetic fields of arbitrary orientations. Spatial dispersion was taken into account. The external field configurations at which its influence could be ignored were found. Asymptotic equations for the field dependences of the absorption coefficient and refractive index were obtained. The neglect of the spin of particles was shown to lead to a fundamentally false idea of magnetic field effects on the optical properties of nonconducting crystals.

VACUUM POLARIZATION IN QED WITH WORLD-LINE METHODS

The application of world-line techniques to calculation of the vacuum polarization and effective action in scalar and spinor QED with external arbitrary constant electromagnetic field configuration is presented.

Parity Violating Energy Shifts in Atoms, I

We present a study of parity (P) violating contributions to the eigenenergies of stationary systems containing atoms in spatially inhomogeneous external electric fields. In this context the subtle interplay of P-violation and time reversal (T) invariance plays an important role. If the entire field configuration is chosen to exhibit chirality the energies are in general shifted by pseudoscalar contributions which change sign under a planar reflection of the field. In part I we consider sudden variations of the fields and calculate P-violating energy shifts using perturbation theory. In part II the adiabatic case will be treated and the connection to geometrical (Berry-) phases will be elucidated. To calculate the effects we use the standard model of elementary particle physics where the P-odd interaction arises through the exchange of Z-bosons between the quarks in the nucleus and the atomic electrons. We consider in detail hydrogen-like systems in unstable levels of principal quantum number n = 2. We study atoms with vanishing nuclear spin like $$_{1}^{1}{\rm He}^{+}$$ and with nuclear spin I = 1/2 like $$_{1}^{1}{\rm H}$$ . The nominal order of P-violating effects is 10−5...10−9 Hz which is determined by the mixing of the 2S1/2 and 2P1/2 states. However we point out that with certain configurations of the external fields, it is possible to enhance the P-violating energy shifts dramatically! Instead of energy shifts linear in the P-violation parameters we get then shifts proportional to the square root of these parameters. Numerically we find such energy shifts which only appear for unstable states to be of order 10−5...1 Hz. Under a reversal of the handedness of the external field configuration these P-violating shifts get multiplied by a phase factor i, i.e. the shifts in the real and imaginary part of the complex eigenenergies are exchanged. Application of our technique to hydrogen-like atoms with a nucleus of spin I = 1/2 yields P-violating energy shifts which are very sensitive to the nuclear spin dependent P-odd force, which receives a rather large contribution from the polarized strange quark density in polarized nuclei. Thus, a measurement of these energy shifts could provide an important tool to elucidate nuclear properties connected to the so called “spin crisis”. We also present a method for treating degenerate perturbation theory which combines advantages of both, Kato’s and Bloch’s methods.