arXiv subjects

Pavel A. Andreev

Publications and source records attributed to Pavel A. Andreev.

At least 55 records · Page 3Linked to original sources

arXiv2019

Dipolar-drift and collective instabilities of skyrmions in crossed nonuniform electric and magnetic fields in a chiral magnetic insulator

Skyrmions dynamics in the approximation of point-particle skyrmions is considered in the multiferroic insulators, where the spiral magnetic structure is accompanied by finite electric dipole moment. The skyrmion motion is studied in the gradients of perpendicular magnetic and electric fields. The nonuniform magnetic field with a fixed gradient magnitude leads to the spiral motion, where skyrmion circulates in the plane perpendicular to the direction of magnetic field. The frequency of circulation is fixed by the derivative of the external magnetic field and the magnitude of the dipole moment. Application of additional electric field which perpendicular to the magnetic field, but their gradients have same direction leads to the drift motion of skyrmions resulting in the magneto-dipolar Hall effect. Hydrodynamics of the gas of interacting skyrmions in crossed nonuniform electric and magnetic fields shows the new type of hydrodynamical instability caused by the drift motion. Three regimes of instability are described.

cond-mat.mes-hall↗

arXiv2018

Hydrodynamic model of BEC with anisotropic short range interaction and the bright solitons in the repulsive BEC

The quantum hydrodynamic model is developed for the axial symmetric anisotropic short-range interaction. The quantum stress tensor presents the interaction. It is derived up to the third order by the interaction radius. The first order by the interaction radius contains the isotropic part only. It leads to the interaction in the Gross-Pitaevskii approximation. Terms existing in the third order by the interaction radius are caused by the isotropic and nonisotropic parts of the interaction. Each of them introduces the interaction constant. Therefore, three interaction constants are involved in the model. Atoms, except the alkali and alkali-earth atoms, can have anisotropic potential of interaction, particularly it is demonstrated for the lanthanides. The short-wavelength instability caused by the nonlocal terms appears in the Bogoliubov spectrum. Conditions for the stable and unstable behaviour are described. Bright solitons in the repulsive BEC are studied under influence of the anisotropic short-range interaction in the BEC of one species. Area of existence of this bright solitons corresponds to the area of the instability of the Bogoliubov spectrum. Approximate reduction of the nonlocal nonlinearity to the quintic nonlinearity at the description of the bright solitons is demonstrated either.

cond-mat.quant-gas↗

arXiv2018

Electrostatic Langmuir and SEAWs in spin polarized plasma double layer

The quantum hydrodynamic model of the electrostatic waves in the two parallel layers of two dimensional electron gases (2DEGs) is developed. It is considered for two regimes: classic regime and quantum regime with the separate spin evolution. Two Langmuir-like waves are found in classic case which have an interference-like pattern in the frequency dependence on concentration $ω^{2}\sim(n_{01}+n_{02}\pm2\sqrt{n_{01}n_{02}})$. They appear instead of two 2D Langmuir waves in noninteracting 2DEGs. The spectrum of four waves is found in the quantum regime. Two extra waves are related to the separate spin evolution and associated to the spin-electron acoustic waves. The influence of the quantum Bohm potential is considered either.

physics.plasm-ph↗

arXiv2018

Extraordinary SEAWs under influence of the spin-spin interaction and the quantum Bohm potential

The separate spin evolution (SSE) of electrons causes the existence of the spin-electron acoustic wave. Extraordinary spin-electron acoustic waves (SEAWs) propagating perpendicular to the external magnetic field have large contribution of the transverse electric field. Its spectrum has been studied in the quasi-classical limit at the consideration of the separate spin evolution. The spin-spin interaction and the quantum Bohm potential give contribution in the spectrum extraordinary SEAW. This contribution is studied in this paper. Moreover, it is demonstrated that the spin-spin interaction leads to the existence of the extraordinary SEAWs if the SSE is neglected. The hybridization of the extraordinary SEAW and the lower extraordinary wave in the regime, where the cyclotron frequency is larger then the Langmuir frequency is studied either.

physics.plasm-ph↗

arXiv2018

Spin current contribution in the spectrum of collective excitations of degenerate partially polarized spin-1/2 fermions at separate dynamics of spin-up and spin-down fermions

The spectrum of collective excitations of degenerate partially polarized spin-1/2 fermions is considered. The spin-up fermions and the spin-down fermions are considered as different fluids. Corresponding two-fluid hydrodynamics consistent with a non-linear Pauli equation is suggested. An equation of state for the spin current caused by the distribution of particles on different energy levels is suggested for the degenerate regime, where the spin current is caused by the Pauli blocking. Spectrum of three waves is found as a solution of the hydrodynamic equations: two sound waves and one spin wave. Their spectrums are calculated for two regimes: propagation parallel and perpendicular to the direction of the equilibrium spin polarization.

cond-mat.quant-gas↗

arXiv2017

Oblique propagation of longitudinal spin-electron acoustic waves under the influence of the Coulomb exchange interaction and the quantum Bohm potential

Influence of the exchange interaction on the properties of the spin-electron acoustic waves at the oblique propagation of waves relatively to the external magnetic field in the magnetically ordered metals is studied. The spectra of the Langmuir wave and the Trivelpiece-Gould wave are also considered. It is well-known that there are two branches of spectrum of the spin-electron acoustic waves in this regime. Change their properties under influence of the exchange interaction is studied. The quantum Bohm potential is included either. The exchange interaction and quantum Bohm potential gives opposite contributions, but they do not compensate each other since they have different dependence on the wave vector. This competition creates a non-monotonical behavior of the Trivelpiece-Gould wave spectrum. The concavity changes in the monotonic spectra of the Langmuir wave and the SEAWs are found.

physics.plasm-ph↗

arXiv2017

Kinetic description of the oblique propagating spin-electron acoustic waves in degenerate plasmas

Oblique propagation of the spin-electron acoustic waves in degenerate magnetized plasmas is considered in terms of quantum kinetics with the separate spin evolution, where the spin-up electrons and the spin-down electrons are considered as two different species with different equilibrium distributions. It is considered in the electrostatic limit. Corresponding dispersion equation is derived. Analytical analysis of the dispersion equation is performed in the long-wavelength limit to find an approximate dispersion equation describing the spin-electron acoustic wave. The approximate dispersion equation is solved numerically. Real and imaginary parts of the spin-electron acoustic wave frequency are calculated for different values of the parameters describing the system. It is found that the increase of angle between direction of wave propagation and the external magnetic field reduces the real and imaginary parts of spin-electron acoustic wave frequency. The increase of the spin polarization decreases the real and imaginary parts of frequency either. The imaginary part of frequency has nonmonotonic dependence on the wave vector which shows a single maximum. The imaginary part of frequency is small in compare with the real part for all parameters in the area of applicability of the obtained dispersion equation.

physics.plasm-ph↗

arXiv2017

Dielectric permeability tensor and linear waves in spin-1/2 quantum kinetics with non-trivial equilibrium spin-distribution functions

A consideration of waves propagating parallel to the external magnetic field is presented. The dielectric permeability tensor is derived from quantum kinetic equations with non-trivial equilibrium spin-distribution functions (NTESDF) in the linear approximation on amplitude of wave perturbations. In general case, x- and y-projections of the SDF are nonzero which is called the non-trivial regime. Corresponding equilibrium solution is found. Contribution of the NTESDF appears in the dielectric permeability tensor in the additive form. It is explicitly found here. Corresponding modification in the dispersion equation for the transverse waves is derived. Contribution of NTESDF in the spectrum of transverse waves is calculated numerically. It is found that the term caused by the NTESDF can be comparable with the classic terms for the relatively small wave vectors and frequencies above the cyclotron frequency. In majority of regimes, the extra spin caused term dominates over the spin term found earlier, except the small frequency regime, where their contributions in the whistler spectrum are comparable. A decrease of the left-hand circularly polarized wave frequency, an increase of the high-frequency right-hand circularly polarized wave frequency, and a decrease of frequency changing by an increase of frequency at the growth of the wave vector for the whistler are found. A dramatic decrease of the spin wave frequency resulting in several times larger group velocity of the spin wave is found either. Found dispersion equations are used for obtaining of an effective quantum hydrodynamics reproducing these results. This generalization requires the introduction of corresponding equation of state for the thermal part of the spin current in the spin evolution equation.

physics.plasm-ph↗

arXiv2016

Kinetic analysis of spin current contribution to spectrum of electromagnetic waves in spin-1/2 plasma, Part II: Dispersion dependencies

The dielectric permeability tensor for spin polarized plasmas derived in terms of the spin-1/2 quantum kinetic model in six-dimensional phase space in Part I of this work is applied for study of spectra of high-frequency transverse and transverse-longitudinal waves propagating perpendicular to the external magnetic field. Cyclotron waves are studied at consideration of waves with electric field directed parallel to the external magnetic field. It is found that the separate spin evolution modifies the spectrum of cyclotron waves. These modifications increase with the increase of the spin polarization and the number of the cyclotron resonance. Spin dynamics with no account of the anomalous magnetic moment gives a considerable modification of spectra either. The account of anomalous magnetic moment leads to a fine structure of each cyclotron resonance. So, each cyclotron resonance splits on three waves. Details of this spectrum and its changes with the change of spin polarization are studied for the first and second cyclotron waves. A cyclotron resonance existing at $ω\approx0.001\midΩ_{e}\mid$ due to the anomalous magnetic moment is also described, where $\midΩ_{e}\mid$ is the cyclotron frequency. The ordinary waves does not have any considerable modification. The electrostatic and electromagnetic Berstein modes are studied during the analysis of waves propagating perpendicular to the external magnetic field with the electric field perturbation directed perpendicular to the external field. A modification of the oscillatory structure caused by the equilibrium spin polarization is found in both regimes. Similar modification is found for the extraordinary wave spectrum.

physics.plasm-ph↗

arXiv2016

Kinetic analysis of spin current contribution to spectrum of electromagnetic waves in spin-1/2 plasma, Part I: Dielectric permeability tensor for magnetized plasmas

The dielectric permeability tensor for spin polarized plasmas is derived in terms of the spin-1/2 quantum kinetic model in six-dimensional phase space. Expressions for the distribution function and spin distribution function are derived in linear approximations on the path of dielectric permeability tensor derivation. The dielectric permeability tensor is derived the spin-polarized degenerate electron gas. It is also discussed at the finite temperature regime, where the equilibrium distribution function is presented by the spin-polarized Fermi-Dirac distribution. Consideration of the spin-polarized equilibrium states opens possibilities for the kinetic modeling of the thermal spin current contribution in the plasma dynamics.

physics.plasm-ph↗

arXiv2016

Extraordinary waves in two dimensional electron gas with separate spin evolution and Coulomb exchange interaction

Hydrodynamics analysis of waves in two-dimensional degenerate electron gas with the account of separate spin evolution is presented. The transverse electric field is included along with the longitudinal electric field. The Coulomb exchange interaction is included in the analysis. In contrast with the three-dimensional plasma-like mediums the contribution of the transverse electric field is small. We show the decrease of frequency of both the extraordinary (Langmuir) wave and the spin-electron acoustic wave due to the exchange interaction. Moreover, spin-electron acoustic wave has negative dispersion at the relatively large spin-polarization. Corresponding dispersion dependencies are presented and analyzed.

physics.plasm-ph↗

arXiv2016

Separated spin evolution quantum hydrodynamics of degenerated electrons with spin-orbit interaction and extraordinary wave spectrum

To consider a contribution of the spin-orbit interaction in the extraordinary wave spectrum we derive a generalization of the separate spin evolution quantum hydrodynamics. Applying corresponding nonlinear Pauli equation we include Fermi spin current contribution in the spin evolution. We find that the spectrum of extraordinary waves consists of three branches: two of them are well-known extraordinary waves and the third one is the spin-electron acoustic wave (SEAW). Earlier SEAWs have been considered in the electrostatic limit. Here we include the electromagnetic effects in their spectrum at the propagation perpendicular to the external magnetic field. We find that the SEAW spectrum considerably changes at the account of transverse part of electric field. We obtain that the separate spin evolution modifies spectrum of the well-known extraordinary waves either. A change of the extraordinary wave spectrum due to the spin-orbit interaction is obtained as well.

physics.plasm-ph↗

arXiv2016

Nonlinear separate spin evolution in degenerate electron-positron-ion plasmas

The non-linear evolution of spin-electron acoustic, positron-acoustic, and spin-electron-positron acoustic waves is considered. It is demonstrated that weakly nonlinear dynamics of each wave leads to the soliton formation. Altogether, we report on existence of three different solitons. The spin-electron acoustic soliton known for electron-ion plasmas is described for electron-positron-ion plasmas for the first time. The existence of the spin-electron-positron acoustic soliton is reported for the first time. The positron-acoustic soliton and the spin-electron-positron acoustic soliton arise as the areas of a positive electric potential. The spin-electron acoustic soliton behaves as the area of a negative electric potential at the relatively small positron imbalance $n_{0p}/n_{0e}=0.1$ and as the area of a positive electric potential at the relatively large positron imbalance $n_{0p}/n_{0e}=0.5$.

physics.plasm-ph↗

arXiv2016

On the rich eight branch spectrum of the oblique propagating longitudinal waves in partially spin polarized electron-positron-ion plasmas

We consider the separate spin evolution of electrons and positrons in electron-positron and electron-positron-ion plasmas. We consider oblique propagating longitudinal waves in this systems. We report presence of the spin-electron acoustic waves and their dispersion dependencies. In electron-positron plasmas, similarly to the electron-ion plasmas, we find one spin-electron acoustic wave (SEAW) at propagation parallel or perpendicular to the external field and two spin-electron acoustic waves at the oblique propagation. At the parallel or perpendicular propagation of the longitudinal waves in electron-positron-ion plasmas we find four branches: the Langmuir wave, the positron-acoustic wave and pair of waves having spin nature, they are the SEAW and, as we called it, spin-electron-positron acoustic wave (SEPAW). At the oblique propagation we find eight longitudinal waves: the Langmuir wave, Trivelpiece-Gould wave, pair of positron-acoustic waves, pair of SEAWs, and pair of SEPAWs. Thus, for the first time, we report existence of the second positron-acoustic wave existing at the oblique propagation and existence of SEPAWs.

physics.plasm-ph↗

arXiv2015

Surface spin-electron acoustic waves in magnetically ordered metals

Degenerate plasmas with motionless ions show existence of three surface waves: the Langmuir wave, the electromagnetic wave, and the zeroth sound. Applying the separated spin evolution quantum hydrodynamics to half-space plasma we demonstrate the existence of the surface spin-electron acoustic wave (SSEAW). We study dispersion of the SSEAW. We show that there is hybridization between the surface Langmuir wave and the SSEAW at rather small spin polarization. In the hybridization area the dispersion branches are located close to each other. In this area there is a strong interaction between these waves leading to the energy exchange. Consequently, generating the Langmuir waves with the frequencies close to hybridization area we can generate the SSEAWs. Thus, we report a method of creation of the SEAWs.

physics.plasm-ph↗

arXiv2015

On a mechanism of high-temperature superconductivity: Spin-electron acoustic wave as a mechanism for the Cooper pair formation

We have found the mechanism of the electron Cooper pair formation via the electron interaction by means of the spin-electron acoustic waves. This mechanism takes place in metals with rather high spin polarization, like ferromagnetic, ferrimagnetic and antiferromagnetic materials. The spin-electron acoustic wave mechanism leads to transition temperatures 100 times higher than the transition temperature allowed by the electron-phonon interaction. Therefore, spin-electron acoustic waves give the explanation for the high-temperature superconductivity. We find that the transition temperature has strong dependence on the electron concentration and the spin polarization of the electrons.

cond-mat.supr-con↗

arXiv2015

On equation of state for the "thermal" part of the spin current: Pauli principle contribution in the spin wave spectrum in cold fermion system

Spin evolution opened a large field in quantum plasma research. The spin waves in plasmas were considered among new phenomena considered in spin-1/2 quantum plasmas. The spin density evolution equation found by means of the many-particle quantum hydrodynamics shows existence of the "thermal" part of the spin current, which is an analog of the thermal pressure, or the Fermi pressure for degenerate electron gas, existing in the Euler equation. However, this term has been dropped, since there has not been found any equation of state for the thermal part of the spin current (TPSC), like we have for the pressure. In this paper we derive the equation of state for the TPSC and apply it for study of spectrum of collective excitations in spin-1/2 quantum plasmas. We focus our research on the spectrum of spin waves, since this spectrum is affected by the thermal part of the spin current. We consider two kinds of plasmas: electron-ion plasma with motionless ions and degenerate electrons, and degenerate electron-positron plasmas. We also present the non-linear Pauli equation with the spinor pressure term containing described effects. The thermal part of the flux of spin current existing in the spin current evolution equation is also derived. We also consider the contribution of the TPSC in the grand generalized vorticity evolution.

physics.plasm-ph↗

arXiv2015

Spin electron acoustic soliton: Separate spin evolution of electrons with exchange interaction

Separate spin evolution quantum hydrodynamics is generalized to include the Coulomb exchange interaction. The Coulomb exchange interaction is considered as the interaction between the spin-down electrons being in the quantum states occupied by one electron, giving main contribution in the equilibrium. The generalized model is applied to study the non-linear spin-electron acoustic waves. Existence of the spin-electron acoustic soliton is demonstrated. Contributions of the concentration, spin polarization, and exchange interaction in the properties of the spin electron acoustic soliton are studied.

physics.plasm-ph↗