arXiv subjects

E. P. Yukalova

Publications and source records attributed to E. P. Yukalova.

At least 145 records · Page 8Linked to original sources

arXiv2001

Dynamic Critical Phenomena in Trapped Bose Gases

Nonlinear dynamics of a trapped Bose-Einstein condensate, subject to the action of a resonant external field, is studied. This field produces a spatio-temporal modulation of the trapping potential with the frequency close to the transition frequency between the ground state and a higher energy level. The evolution equations of fractional populations display a kind of critical phenomena at a critical line on the manifold of the system parameters. It is demonstrated that there exists a direct analogy between dynamical instability at this line and critical phenomena at a critical line of a related averaged system.

cond-mat↗

arXiv2001

Crystal Symmetry and Time Scales

The relation between the notion of crystalline symmetry and characteristic time intervals when this symmetry could be observed is analyzed. Several time scales are shown to exist for a system of interacting particles. It is only when the observation time is much larger than the mesoscopic fluctuation time, the notion of crystalline symmetry becomes physically meaningful. The ideas are concretized by a two-phase lattice model.

cond-mat↗

arXiv2001

Nonground State Condensates of Ultracold Trapped Atoms

The population dynamics of a trapped Bose-Einstein condensate, subject to the action of an oscillatory field, is studied. This field produces a modulation of the trapping potential with the frequency close to the transition frequency between the ground state and an excited energy level. Unusual critical effects are found exhibiting sharp qualitative changes in the population dynamics. An effective averaged system is constructed explicitly illustrating the occurrence of critical phenomena. The related critical indices are calculated.

cond-mat↗

arXiv2001

Enhancement of Nuclear Spin Superradiance by Electron Resonator

Superradiance of nuclear spins is considered, when the nuclei interact via hyperfine forces with electrons of a ferromagnet. The consideration is based on a microscopic model. If the sample, coupled with a resonant electric circuit, possesses electronic magnetization, then the electron subsystem plays the role of an additional effective resonator, by enhancing the coupling between nuclear spins and the resonant circuit. Radiation power can be increased by three orders, while the radiation time of a superradiance burst can become three times shorter. In the presence of dynamic nuclear polarization, the regime of pulsing superradiance can occur.

cond-mat↗

arXiv2000

Cooperative Electromagnetic Effects

Collective phenomena in strongly nonequilibrium systems interacting with electromagnetic field are considered. Such systems are described by complicated nonlinear differential or integro-differential equations. The aim of this review is to show that many nonlinear collective phenomena can be successfully treated by a recently developed method called the Scale Separation Approach whose name is due to the idea of separating different characteristic space-time scales existing in nonequilibrium statistical systems. This approach is rather general and can be applied to various nonequilibrium physical problems, several of which are discussed here. The problems considered not only serve as illustrations of the method but are quite important by themselves presenting interesting physical effects, such as Collective Liberation of Light, Turbulent Photon Filamentation, Superradiant Spin Relaxation, Negative Electric Current, and Magnetic Semiconfinement of Atoms.

cond-mat↗

arXiv2000

Equation of State in Quantum Chromodynamics

The equation of state for quark-gluon plasma is obtained, being valid for arbitrary values of the coupling parameter and of temperature. This equation is constructed from perturbative expansions for free energy and for renormalization function. Summation of asymptotic perturbative series is accomplished by means of the self-similar approximation theory.

hep-ph↗

arXiv2000

Excited Coherent Modes of Ultracold Trapped Atoms

A method of exciting coherent spatial modes of Bose-condensed trapped atoms is considered. The method is based on the resonance modulation of the trapping potential. The population dynamics of coherent modes is analysed. The method makes it possible to create mixtures of different spatial modes in arbitrary proportions, including the formation of pure excited coherent modes. Novel critical effects in the population dynamics are found.

cond-mat↗

arXiv2000

Formation of Directed Beams from Atom Lasers

The problem of creating well-collimated beams of atoms escaping from a trap is studied. This problem is of high importance for the realization of atom lasers. Nonadiabatic dynamics of neutral atoms in nonuniform magnetic fields, typical of quadrupole magnetic traps, has been considered. The main result of this report is that an unusual semiconfining regime of motion is found, when atoms are confined from one side of an axis but are not confined from another side. This regime can be achieved by means of only magnetic fields. The formed atomic beam can be forwarded in arbitrary direction.

cond-mat↗

arXiv2000

Ion-Beam Induced Current in High-Resistance Materials

The peculiarities of electric current in high-resistance materials, such as semiconductors or semimetals, irradiated by ion beams are considered. It is shown that after ion--beam irradiation an unusual electric current may arise directed against the applied voltage. Such a negative current is a transient effect appearing at the initial stage of the process. The possibility of using this effect for studying the characteristics of irradiated materials is discussed. A new method for defining the mean projected range of ions is suggested.

cond-mat↗

arXiv1999

Self-Similar Perturbation Theory

A method is suggested for treating those complicated physical problems for which exact solutions are not known but a few approximation terms of a calculational algorithm can be derived. The method permits one to answer the following rather delicate questions: What can be said about the convergence of the calculational procedure when only a few its terms are available and how to decide which of the initial approximations of the perturbative algorithm is better, when several such initial approximations are possible? Definite answers to these important questions become possible by employing the self-similar perturbation theory. The novelty of this paper is in developing the stability analysis based on the method of multipliers and in illustrating the efficiency of this analysis by different quantum-mechanical problems.

hep-ph↗

arXiv1999

Transient Effect of Negative Electric Current in Irradiated Semiconductors

The peculiarities of electric current are studied occurring in semiconductors with strongly nonuniform distribution of charge carriers. The formation of such nonuniformities and the regulation of carrier mobilities can be realized by means of external irradiation, for instance, charge-particle beams and laser irradiation. The transient effect of negative electric current is shown to arise under some specific conditions.

cond-mat↗

arXiv1999

Collimation Mechanism for Atom Lasers

A mechanism is suggested for creating well-collimated beams of neutral spin-polarized particles by means of magnetic fields. This mechanism can be used in atom lasers for the formation of directed coherent beams of atoms. The directed motion of atoms is achieved only with the help of magnetic fields, no mechanical collimators being involved.

cond-mat↗

arXiv1999

Cannon for Neutral Particles

Dynamics of spin-polarized neutral particles, such as neutrons or neutral atoms and molecules, in magnetic fields is studied. A new regime of motion is found where particles move mainly in one direction forming a well-collimated beam. This regime suggests a mechanism for creating devices emitting directed beams of neutral particles.

cond-mat↗

arXiv1999

Anomalous Transient Current in Nonuniform Semiconductors

Nonequilibrium processes in semiconductors are considered with highly nonuniform initial densities of charge carriers. It is shown that there exist such distributions of charge densities under which the electric current through a sample displays quite abnormal behaviour flowing against the applied voltage. The appearance of this negative electric current is a transient phenomenon occurring at the initial stage of the process. After this anomalous negative fluctuation, the electric current becomes normal, i.e. positive as soon as the charge density becomes more uniform. Several possibilities for the practical usage of this effect are suggested.

cond-mat↗

arXiv1998

Spin Maser under Stationary Pumping

Spin dynamics of a polarized spin system is studied when the latter is coupled with a resonant electric circuit and is under the action of an external pumping supporting a stationary nonequilibrium magnetization. A complete classification of possible regimes of spin motion is given. In addition to seven regimes considered earlier, two other transient regimes are found and thoroughly described: One is an oscillatory regime, when spins always move coherently but the degree of coherence fluctuates with time. Another is a pulsing regime, when spins reveal coherent motion during short pulses separated from each other by intervals of incoherent motion. These regimes are, in principle, transient, although may be extremely long lasting; their duration may be several orders longer than the transverse relaxation time and twice longer than the longitudinal relaxation time. Both transient regimes end with a coherent quasistationary regime.

cond-mat.stat-mech↗

arXiv1998

Self-Similar Interpolation in Quantum Mechanics

An approach is developed for constructing simple analytical formulae accurately approximating solutions to eigenvalue problems of quantum mechanics. This approach is based on self-similar approximation theory. In order to derive interpolation formulae valid in the whole range of parameters of considered physical quantities, the self-similar renormalization procedure is complimented here by boundary conditions which define control functions guaranteeing correct asymptotic behaviour in the vicinity of boundary points. To emphasize the generality of the approach, it is illustrated by different problems that are typical for quantum mechanics, such as anharmonic oscillators, double-well potentials, and quasiresonance models with quasistationary states. In addition, the nonlinear Schrödinger equation is considered, for which both eigenvalues and wave functions are constructed.

cond-mat↗

arXiv1998

Renormalization--Group Solutions for Yukawa Potential

The self--similar renormalization group is used to obtain expressions for the spectrum of the Hamiltonian with the Yukawa potential. The critical screening parameter above which there are no bound states is also obtained by this method. The approach presented illustrates that one can achieve good accuracy without involving extensive numerical calculations, but invoking instead the renormalization--group techniques.

cond-mat↗

arXiv1998

Negative Electric Current in Semiconductors

Electric current in semiconductors is considered as a function of time. Nonequilibrium fluctuations of the current are studied for strongly nonuniform samples. It is demonstrated that at special conditions the total electric current through a device can exhibit a negative fluctuation, when the current is directed against the applied voltage.

cond-mat↗