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I. Ya. Polishchuk

Publications and source records attributed to I. Ya. Polishchuk.

15 recordsLinked to original sources
arXiv2024

A method for measuring deviation from Lambert diffuse scattering law of ultracold neutrons on material walls

Modeling the motion of ultracold neutrons (UCNs) is crucial for assessing their losses, accurately measuring their lifetime, and describing other experiments. In material traps, it is necessary to account not only for specular but also for diffuse elastic reflection of UCNs from the trap walls. Typically, the Lambert cosine law is used to describe the angular distribution of diffusely scattered neutrons. However, this law lacks a rigorous theoretical derivation and is often violated. In our work, we propose an experiment to measure the deviation of the angular distribution of UCNs during diffuse scattering from the Lambert law. This deviation can be determined by the difference in the number of neutrons exiting through the central and end windows of a long narrow UCN trap. Monte Carlo simulations corresponding to a possible experiment have been performed, demonstrating a significant effect for different trap geometries.

physics.ins-det↗
arXiv2021

Bose Einstein condensation and ferromagnetism of low density Bose gas of particles with arbitrary spin

Properties of the ground state and the spectrum of elementary excitations are investigated for the low density ultracold spinor 3D Bose gas of particles with arbitrary nonzero spin. Gross-Pitaevskii equations are derived. Within the framework of the considering interaction Hamiltonian it is shown that the ground state spin structure and spin part of the chemical potential is determined by the renormalized interaction, being defined by the contribution of the virtual large momenta. The ferromagnetic structure of the ground state, and the equation of the phase, density, and spin dynamics are obtained from Gross-Pitaevskii equations.

cond-mat.quant-gas↗
arXiv2017

Guided Modes in the Plane Array of Optical Waveguides

It is known that for an isolated dielectric cylinder waveguide there exists the cutoff frequency $ω_\ast$ below which there is no guided mode. It is shown in the paper that the infinite plane periodic array of such waveguides possesses the guided modes in the frequency domain which is below the frequency $ω_\ast$. In the case of a finite array, the modes in this frequency domain are weakly radiating ones, but their quality factor $Q$ increases with the number of waveguides $N$ as $Q(N)\sim N^3$. This dependence is obtained both numerically, using the multiple scattering formalism, and is justified with a simple analytical model.

cond-mat.mes-hall↗
arXiv2016

Quantum Phase Transition of the Electron-Hole Liquid In the Coupled Quantum Wells

Many-component electron-hole plasma is considered in the Coupled Quantum Wells (CQW). It is found that the homogeneous state of the plasma is unstable if the carrier density is sufficiently small. The instability results in the breakdown into two coexisting phase - a low-density gas phase and a high-density electron-hole liquid. The homogeneous state of the electron-hole liquid is stable if the distance between the quantum wells l is sufficiently small. However, as the distance l increases and reaches a certain critical value, the plasmon spectrum of the electron-hole liquid becomes unstable. Hereupon, a quantum phase transition occurs, resulting in the appearance of the charge density waves of finite amplitude in both quantum wells. The strong mass renormalization and the strong Z-factor renormalization are found for the electron-hole liquid as the quantum phase transition occurs.

cond-mat.str-el↗
arXiv2015

Theory of Optical Bloch Oscillations in the Zigzag Waveguide Array

The Bloch oscillations in the zigzag array of the optical waveguides are considered. The multiple scattering formalism (MSF) is used for the numerical simulation of the optical beam which propagates within the array. The effect of the second-order coupling which depends on the geometrical parameters of the array is investigated. The results obtained within the MSF are compared with the calculation based on the phenomenological coupling modes model. The calculations are performed for the waveguides fabricated in alkaline earth boro-aluminosilicate glass sample, which are the most promising for the C-band (1530-1565 nm).

cond-mat.mes-hall↗
arXiv2014

Electron-Hole Liquid in the Couple Quantum Wells

It is shown that the homogeneous state of the spatially separated electrons and holes in the coupled quantum wells (CQW) is instable if the layer charge density is smaller than the critical value specified by the parameters of the CQW. The effect is due to the many-body Coulomb correlations which provide the positive compressibility. The instability results in the formation of the inhomogeneous system which comprises the liquid electron-hole drops.

cond-mat.mes-hall↗
arXiv2012

Many-body Correlation Effects in the Spatially Separated Electron and Hole Layers in the Coupled Quantum Wells

The many-body correlation effects in the spatially separated electron and hole layers in the coupled quantum wells are investigated. The specific case of the many-component electron-hole system is considered. Keeping the main diagrams in the parameter of the inverse number of components allows us to justify the RPA diagram selection. The ground state of the system is found to be the electron-hole liquid which possesses the energy smaller than the exciton phase. The connection is discussed between the results obtained and the experiments in which the inhomogeneous state in the coupled quantum wells is revealed.

cond-mat.str-el↗
arXiv2011

Optical Bloch oscillation and Zener tunneling in an array of cylindrical waveguides. Numerical simulation

We investigate optical Bloch oscillation, Zener tunneling and breathing modes in arrays of optical waveguides. We perform a new method of calculation based on the multiple scattering formalism. To demonstrate Bloch oscillation and breathing modes, we consider a planar array of parallel cylindrical waveguides with the refractive index gradually varying across the array. We demonstrate that the form of Bloch oscillation may be predicted by means of dispersion law analysis. To demonstrate Zener tunneling, we consider a planar array of cylindrical waveguides of two types situated by turn. The band structure of this array contains two bands separated by a narrow gap. If the refractive indices of waveguides gradually vary across the array, the Zener tunneling leads to the Bloch-Zener oscillation.

cond-mat.mes-hall↗
arXiv2008

Interference of guiding polariton mode in "traffic" circle waveguides composed of dielectric spherical particles

The interference of polariton guiding modes propagating through "traffic circle" waveguides composed of dielectric spherical particles is investigated. The dependence of intensity of the wave on the position of the particle was studied using the multisphere the Mie scattering formalism. We show that if the frequency of light belongs to the passband of the waveguide, electromagnetic waves may be considered as two optical beams running along a circle in opposite directions and interfering with each other. Indeed, the obtained intensity behavior can be represented as a simple superposition of two waves propagating around a circle in opposite directions. The applications of this interference are discussed.

physics.optics↗
arXiv2007

Effect of triple interaction on energy delocalization in the strongly disordered system of interacting two-level defects

We accurately treat the effect of the double and triple interactions of two-level systems (TLS) in glasses onto the energy delocalization due to the long-range interaction of TLS. Although this work qualitatively reproduces the estimates of our previous work we believe that it is important because in this paper the estimates are done with quantitative accuracy. This work can serve as the important step towards the development of quantitative theory of many-body delocalization due to the long-range interaction. Our study is compared with the recent work by Bodea et al claiming that the interaction of TLS triples leads to the energy delocalization. We cannot agree with the mentioned work because as we show the interaction of TLS triples was overestimated there and therefore the result for the TLS relaxation rate obtained there is invalid.

cond-mat.dis-nn↗
arXiv2006

On the theory of resonant susceptibility of dielectric glasses in magnetic field

The anomalous magnetic field dependence of dielectric properties of insulating glasses in the temperature interval $10mK<T<50mK$ is considered. In this temperature range, the dielectric permittivity is defined by the resonant contribution of tunneling systems. The external magnetic field regulates nuclear spins of tunneling atoms. This regulation suppresses a nuclear quadrupole interaction of these spins with lattice and, thus, affects the dielectric response of tunneling systems. It is demonstrated that in the absence of an external magnetic field the nuclear quadrupole interaction $b$ results in the correction to the permittivity $δχ\sim| b| /T$ in the temperature range of interest. An application of a magnetic field results in a sharp increase of this correction approximately by a factor of two when the Zeeman splitting $m$ approaches the order of $| b| $. Further increase of the magnetic field results in a relatively smooth decrease in the correction until the Zeeman splitting approaches the temperature. This smooth dependence results from tunneling accompanied by a change of the nuclear spin projection. As the magnetic field surpasses the temperature, the correction vanishes. The results obtained in this paper are compared with experiment. A new mechanism of the low temperature nuclear spin-lattice relaxation in glasses is considered.

cond-mat.dis-nn↗
arXiv2005

Low temperature breakdown of coherent tunneling in amorphous solids induced by the nuclear quadrupole interaction

We consider the effect of the internal nuclear quadrupole interaction on quantum tunneling in complex multi-atomic two-level systems. Two distinct regimes of strong and weak interactions are found. The regimes depend on the relationship between a characteristic energy of the nuclear quadrupole interaction $λ_{\ast}$ and a bare tunneling coupling strength $Δ_{0}$. When $Δ_{0}>λ_{\ast}$, the internal interaction is negligible and tunneling remains coherent determined by $Δ_{0}$. When $Δ_{0}<λ_{\ast}$, coherent tunneling breaks down and an effective tunneling amplitude decreases by an exponentially small overlap factor $η^{\ast}\ll1$ between internal ground states of left and right wells of a tunneling system. This affects thermal and kinetic properties of tunneling systems at low temperatures $T<λ_{*}$. The theory is applied for interpreting the anomalous behavior of the resonant dielectric susceptibility in amorphous solids at low temperatures $T\leq 5$mK where the nuclear quadrupole interaction breaks down coherent tunneling. We suggest the experiments with external magnetic fields to test our predictions and to clarify the internal structure of tunneling systems in amorphous solids.

cond-mat.dis-nn↗
arXiv2005

Effect of nuclear quadrupole interactions on the dynamics of two-level systems in glasses

The standard tunneling model describes quite satisfactorily the thermal properties of amorphous solids at temperatures $T<1K$ in terms of an ensemble of two-level systems possessing logarithmically uniform distribution over their tunneling amplitudes and uniform distribution over their asymmetry energies. In particular, this distribution explains the observable logarithmic temperature dependence of the dielectric constant. Yet, experiments have shown that at ultralow temperatures $T<5mK$ such a temperature behavior breaks down and the dielectric constant becomes temperature independent (plateau effect). In this letter we suggest an explanation of this behavior exploiting the effect of the nuclear quadrupole interaction on tunneling. We show that below a temperature corresponding to the characteristic energy of the nuclear quadrupole interaction the effective tunneling amplitude is reduced by a small overlap factor of the nuclear quadrupole ground states in the left and right potential wells of the tunneling system. It is just this reduction that explains the plateau effect . We predict that the application of a sufficiently large magnetic field $B>10T$ should restore the logarithmic dependence because of the suppression of the nuclear quadrupole interaction.

cond-mat.dis-nn↗
arXiv2004

The Long Range Interaction and the Relaxation in Glasses at Low Temperatures

We describe the interaction stimulated relaxation in the ensemble of two-level systems, responsible for low temperature kinetics and thermodynamics properties of amorphous solids. This relaxation gets significant at sufficiently low temperature when phonons are substantially frozen out. We show that in the realistic experimental situation the measuring field strongly accelerates the interaction stimulated relaxation. The characteristic temperature and field dependences of the relaxation rate are found when the rate is affected both by the interaction between two level systems and by the external field.

cond-mat.dis-nn↗