bluuebunny/crossref_metadata_2025 huggingface dataset:
Casimir effect in a D-dimensional flat space-time and the cut-off method
Authors: Svaiter N. F. , Svaiter B. F.
Published: July 2002

The Casimir effect in a D-dimensional space time produced by a Hermitian massless scalar field in the presence of a pair of perfectly reflecting parallel flat plates is discussed. The exponential cut-off regularization method is employed. The regularized vacuum energy and the Casimir energy of this field are evaluated and a detailed analysis of the divergent terms in the regularized vacuum energy is carried out. The two-dimensional version of the Casimir effect is discussed by means of the same cut-off method. A comparison between the above method and the zeta function regularization procedure is presented in a way that gives the unification between these methods in the present case.
On the evaluation of the integral over the product of two spherical Bessel functions
Authors: Maximon Leonard C.
Published: July 2002

The integral Il,l′(k,k′)=∫∞0jl (kr)jl′(k′r)r 2 dr, in which the spherical Bessel functions jl(kr) are the radial eigenfunctions of the three-dimensional wave equation in spherical coordinates, is evaluated in terms of distributions, in particular, step functions and delta functions. It will be shown that the behavior of Il,l′ is very different in the cases l−l′ even (0, ±2, ±4, ...) and l−l′ odd (±1, ±3, ...). For l−l′ even it is expressed in terms of the delta function, step functions, and Legendre polynomials. For l−l′ odd it is expressed in terms of Legendre functions of the second kind and step functions; no delta functions appear.
The interaction of outgoing and ingoing spherically symmetric null fluids
Authors: Holvorcem Paulo R. , Letelier Patricio S. , Wang Anzhong
Published: July 2002

Using similarity methods, the Einstein field equations coupled to two oppositely directed null fluids for a spherically symmetric space–time are reduced to an autonomous system of three ordinary differential equations. The space of solutions is studied in some detail and solutions are found that represent: (i) the backscattering of an initially outgoing thick null fluid shell in a background gravitational field with a central naked singularity, (ii) the formation of strong space–time singularities by the interaction of thick null fluid shells, (iii) the interaction of a core of null radiation with an incoming shell of null fluid, and (iv) cosmological models of Kantowski–Sachs type with initial and final singularities clothed by apparent horizons.
On the collapse of a spherically symmetric star
Authors: Kriele Marcus
Published: July 2002

The initial value problem for a compact, spherically symmetric star with a rather general equation of state is discussed. For any given time it is possible to calculate the area of the spheres of symmetry which intersect the boundary, if space–time is C5 and the initial energy density is smooth (i.e., C∞) and satisfies some minor technical conditions. The physical relevance of this result is also discussed.
Damped wave equations with noise
Authors: Elshamy Maged
Published: July 2002

Damped wave equations with random excitation describing the vibrations of a string with a dissipative force are discussed. The sources of such random disturbances are either an initial white noise or a Gaussian random forcing. Let uε(t,x) be the displacement at time t of a point x on a string, where the time variable t≥0, and the space variable x∈R. The random fields uε(t,x) are analyzed in the limit as the intensity of the noise ε tends to zero, and law of large numbers type results are given for the deviations.
A Lagrangian formalism for the Einstein–Yang–Mills equations
Authors: Robinson D. C.
Published: July 2002

A new action principle, in the which the field variables are a sl(2,C)⊕g valued connection one-form, two-form, and multiplier field, is proposed and discussed. The equations of motion are the complex Einstein–Yang–Mills equations with internal symmetry Lie algebra g.
Special-relativistic harmonic oscillator modeled by Klein–Gordon theory in anti-de Sitter space
Authors: Navarro D. J. , Navarro-Salas J.
Published: July 2002

It is shown that the one-particle sector of the Klein–Gordon theory in the universal covering space of the anti-de Sitter space (CAdS) can be interpreted, in a natural way, as a special-relativistic oscillator in Minkowski space. The quantum wave functions have a significantly different behavior with respect to the nonrelativistic ones. The energy spectrum coincides, up to the ground state energy, with that of the nonrelativistic oscillator. The requirement of having the adequate nonrelativistic limit for the special-relativistic oscillator theory turns out to be equivalent to the imposition of the Dirichlet-type boundary condition at spatial infinity on CAdS Klein–Gordon functions.
Relations between the Casimir operators of sl(1|2) and osp(2|2) superalgebras
Authors: Daumens Michel , Minnaert Pierre
Published: July 2002

The superalgebras sl(1|2) and osp(2|2) are isomorphic. Their Casimir operators have been published in the form of a quadratic (K2) and a cubic (K3) operator for sl(1|2) and a quadratic (I2) and a quartic (I4) operator for osp(2|2). In this note we derive the algebraic relations between both sets of Casimir operators.
Classification of invariant wave equations
Authors: Heredero Rafael Hernández , Olver Peter J.
Published: July 2002

In this paper we characterize the possible symmetry groups of wave equations and certain evolutionary generalizations, in a single time variable and one or more spatial variables. Furthermore, we describe a complete classification of two-dimensional wave equations utt=F[u] and potential evolutionary equations uxt=F[u] having a point or contact symmetry group. The results rely on Lie’s classification of planar transformation groups and their relative differential invariants.
Space–time averages in macroscopic gravity and volume-preserving coordinates
Authors: Mars Marc , Zalaletdinov Roustam M.
Published: July 2002

The definition of the covariant space-time averaging scheme for the objects (tensors, geometric objects, etc.) on differentiable metric manifolds with a volume n-form, which has been proposed for the formulation of macroscopic gravity, is analyzed. An overview of the space-time averaging procedure in Minkowski space-time is given and comparison between this averaging scheme and that adopted in macroscopic gravity is carried out throughout the paper. Some new results concerning the algebraic structure of the averaging operator are precisely formulated and proved, the main one being that the averaging bilocal operator is idempotent iff it is factorized into a bilocal product of a matrix-valued function on the manifold, taken at a point, by its inverse at another point. The previously proved existence theorems for the averaging and coordination bilocal operators are revisited with more detailed proofs of related results. A number of new results concerning the structure of the volume-preserving averaging operators and the class of proper coordinate systems are given. It is shown, in particular, that such operators are defined on an arbitrary n-dimensional differentiable metric manifold with a volume n-form up to the freedom of (n−1) arbitrary functions of n arguments and 1 arbitrary function of (n−1) arguments. All the results given in this paper are also valid whenever appropriate for affine connection manifolds including (pseudo)-Riemannian manifolds.
From Turbiner’s quasi-exactly soluble potentials in N dimensions to analytic solutions of the combined Coulomb plus oscillator system
Authors: Mavromatis Harry A.
Published: July 2002

Turbiner’s one-dimensional, quasi-exactly soluble potentials can be interpreted as central potentials in N dimensions. Using a particular transformation, one shows how these potentials convert to seemingly unrelated isolated solutions of other Schrödinger equations, including solutions of the combined Coulomb plus harmonic oscillator system.
Alternative potentials for the electromagnetic field
Authors: Mosley Shaun N.
Published: July 2002

The source-free electromagnetic field can be expressed in terms of two complex potentials α,β, which are related to the Debye potentials. The potentials {α,β} corresponding to various fields are discussed. A conserved radiation density ρ can be constructed in terms of these potentials, this density is positive (negative) for positive (negative) helicity radiation.
Sigma models coupled with Abelian gauge fields
Authors: O’Keeffe D. , Tchrakian D. H. , Yang Yisong
Published: July 2002

Two distinct Skyrme terms for the CP1 model are defined, only one of which preserves the equivalence with the corresponding O(3) model. A gauging prescription in which the composite connection of the CP1 model is replaced by the U(1) gauge connection is defined. A U(1) gauged CP1 model and two distinct U(1) gauged CP1 models with Skyrme terms are defined. The existence of topologically stable vortices in each of the three U(1) gauged models is proved analytically.
A harmonic space approach to quantum gravity of stationary space–times with SO(3) symmetry
Authors: Hollmann Helia
Published: July 2002

After dimensional reduction the stationary sector of SO(3) symmetric Einstein’s gravity is identified with an SL(2,ℝ)/SO(2) Sigma model coupled to a one-dimensional gravitational remnant. The space of classical solutions consists of the Schwarzschild and Taub–NUT family. A Dirac quantization of this system is performed and the observables—the mass and the charge operator—are shown to be self-adjoint operators with a continuous spectrum ranging from −∞ to ∞. The Hilbert space is constructed explicitly using a harmonic space approach.
On the Groenewold–Van Hove problem for R2n
Authors: Gotay Mark J.
Published: July 2002

We discuss the Groenewold–Van Hove problem for R2n, and completely solve it when n=1. We rigorously show that there exists an obstruction to quantizing the Poisson algebra of polynomials on R2n, thereby filling a gap in Groenewold’s original proof. Moreover, when n=1 we determine the largest Lie subalgebras of polynomials which can be consistently quantized, and explicitly construct all their possible quantizations.
Rayleigh-type vibrations localized at the free surface of a fcc crystal
Authors: Kosevich A. M. , Matsokin D. V. , Savotchenko S. E.
Published: July 2002

The waves localized near the free surface (001) of a fcc crystal and propagating along the [110] direction are analyzed in the model of central interaction of nearest neighbors. The frequencies of these waves fall in the gaps of the frequency spectrum of bulk harmonic vibrations for a fixed value of the wave vector k along the surface. The long-wave limit and the case of wave vectors close to the Brillouin zone boundary are studied analytically. These limiting dependences are in accord with the results obtained earlier by other authors by numerical methods. The analytical calculations in the limiting intervals of vector k are supplemented with numerical calculations for arbitrary values of wave vectors. It is significant that the waves under investigation have a displacement component perpendicular to the crystal surface and hence can be studied by standard methods of inelastic scattering of helium atoms.
Effect of electron–phonon relaxation on longitudinal electron focussing in metals
Authors: Kolesnichenko Yu. A. , Bedassa Tesgera
Published: July 2002

Feasibility of spectroscopy of the electron–phonon interaction (EPI) is substantiated by the method of longitudinal electron focusing (LEF) in thin metal plates. It is shown that the LEF makes it possible to obtain information on the differential function of the EPI characterizing the relaxation of charge carriers with a strictly definite momentum on phonons, which cannot be gained by using other methods.
Ballistic transport and interband interference in two-dimensional quantum contacts
Authors: Moskalets M. V.
Published: July 2002

A new effect, viz., the oscillatory dependence of the collector current on the diameter of the diagram confining the electron flow from the emitter to the collector, is considered. Such a dependence is due to a change in the position of conducting subbands of the diaphragms upon a change in its diameter. It is also shown that the collector current contains a noticeable interference component (associated with the Aharonov–Bohm effect and corresponding to the mixing of conduction channels of the quantum diaphragm) in the case of a strong mismatching of electron states outside and inside the diaphragm.
On self-consistent determination of the quasi-average in statistical physics
Authors: Poluektov Yu. M.
Published: July 2002

The concept of quasi-average introduced by N. N. Bogoliubov for describing the states of many-particle systems with spontaneously broken symmetry (superfluid liquids, superconductors, crystals, etc.) is generalized so that the fields introduced into the initial Hamiltonian for breaking its symmetry are not presumed to be given from outside, but are determined by the properties of the physical object itself and can be found by solving the system of equations in the self-consistent field approximation.
Effect of spontaneous magnetization on the electrical conductivity of ferromagnet-based metallic multilayers
Authors: Kolesnichenko Yu. A. , Dekhtyaruk L. V.
Published: July 2002

The conductivity of metallic magnetic multilayers (MML) in which the thickness of the ferromagnetic component exceeds the Larmor radius r of charge carrier trajectory in the field of spontaneous magnetic induction B, but is smaller than their mean free path l, is studied theoretically. It is shown that, if the electron scattering at the boundaries is negligible, the MML conductivity σ⊥ at right angles to the field B depends significantly on the probability Q of tunneling of charge carriers from layer to layer, as well as on the ratio of radius r and thickness d of the nonmagnetic metal layers. A considerable decrease in the value of σ⊥ upon a transition from antiferromagnetic to ferromagnetic ordering of spontaneous magnetic moments is predicted if the probability Q≫d/l, r/l. The trajectory effects change the anisotropy of the conducting properties of MML in the plane parallel to the boundary.
Quantized vortices in systems with pairing of spatially separated electrons and holes
Authors: Shevchenko S. I.
Published: July 2002

It is predicted that in systems with pairing of spatially separated electrons and holes the planar vortices, in which the electron-hole pairs rotate in the plane of the structure, can become energy-advantageous in a nonuniform magnetic field. In this case the vortices should form an ordered, though translation-noninvariant, structure.
Neutron scattering study of liquid helium. Analysis of new data
Authors: Blagoveshchenskii N. M. , Puchkov A. V. , Skomorokhov A. N. , Bogoyavlenskii I. V. , Karnatsevich L. V.
Published: July 2002

A new analysis of neutron scattering data obtained earlier for liquid He4 is presented. The experiments were made on the time-of- flight spectrometer DIN-2PI in the pulsed reactor IBR-2. The results are analyzed by using a consistent data processing technique including the representation of the dynamic structural factor S(Q,ω) with a constant wave vector Q. The one-phonon component of S(Q,ω) is approximated by using the damped harmonic oscillator function taking into account the instrumental resolution. It is shown that the experimental values of S(Q,ω) are in good agreement with the fitting model, i.e., have a simple one-component structure. The presented results indicate a peculiarity in the temperature dependence of S(Q,ω) for liquid helium in the wave vector region 0.5–0.8 Å−1. Various explanations of such a peculiarity are discussed.
Anyon exciton: Spherical geometry
Authors: Apalkov V. M. , Apalkov D. M.
Published: July 2002

An anyon exciton formed by a valence hole and three quasielectrons of the Laughlin incompressible liquid of the fractional quantum Hall effect with the filling factor ν=1/3 is investigated numerically in a spherical geometry. The quasielectrons ar treated as Bose particles with hard cores and the Coulomb interaction. The energy spectrum of the system and the quasielectron density distribution around the hole are obtained. The energy spectrum of the system has branches which can be classified according to intrinsic angular momentum of an anyon exciton; the absence of branches with an angular momentum below three and a branch with an angular momentum equal to four is a consequence of the Pauli exclusion principle for quasielectrons.
The role of La atoms in the formation of a low-temperature heat-capacity anomaly in cuprates La2CuO4,La2−xMxCuO4(M= Sr, Ba) and Nd2−xLaxCuO4
Authors: Kvavadze K. A. , Nadareishvili M. M. , Basilia G. G. , Igitkhanishvili D. D. , Tarkhnishvili L. A. , Dvali Sh. V.
Published: July 2002

The low-temperature heat capacity of cuprates(La2CuO4,La2−xMxCuO4(M = Sr, Ba) and Nd2−xLaxCuO4) is studied in the temperature range 2–45 K by using pulsed differential calorimetry. It is found that the coefficient of the linear term of heat capacity remains unchanged over the entire temperature interval under investigation. The special role of La atoms in the formation of the anomaly in the acoustic region of the phonon spectrum of these compounds near 6 meV is demonstrated. This anomaly is connected with peculiarities in the interaction of these atoms with the environment.
High-density effects due to interaction of self-trapped exciton with (Ba, 5p) core hole in BaF2 at low temperature
Authors: Terekhin M. A. , Svechnikov N. Yu. , Tanaka S. , Hirose S. , Kamada M.
Published: July 2002

The effect of VUV undulator excitation intensity on the emission shape and decay time of BaF2 crystal at low temperature has been observed. The findings are explained in terms of quenching of Auger-free luminescence (cross luminescence) by self-trapped exciton via Förster mechanism energy transfer.
Simulation of resistive state of a granular superconductor
Authors: Ignatjev V. K.
Published: July 2002

The equation for hypervortex in a slightly granular superconductor is obtained, and the vortex lattice is numerically simulated. The dissipation associated with the formation, collapse, and movement of hypervortices is considered. The equations describing the dynamics of magnetic field distribution, nonlinear susceptibility, and current–voltage characteristics in the resistive state are obtained. The numerically simulated equations give results that are in good agreement with those obtained experimentally.
Anisotropic pinning and the mixed-state galvanothermomagnetic properties of superconductors—a phenomenological approach
Authors: Shklovskij V. A.
Published: July 2002

In the presence of isotropic and anisotropic pinning the vortex dynamics is discussed in terms of phenomenologically introduced, nonlinear viscosities. The formulas for linear galvanothermomagnetic effects are derived and analyzed under the condition at which the transport current or temperature gradient is directed at arbitrary angle with respect to the unidirected twins, which cause the anisotropic pinning. It is shown that two new effects which appear due to the anisotropic pinning, namely (with respect to the reversal of the magnetic field direction) even transverse and odd longitudinal voltage, have a distinct origin. The first is due to the guided vortex motion, while the second appears only when anisotropic (in contrast with isotropic) pinning changes the Hall drag coefficient. We also show that the last effect might be masked in the experiment by a large, odd contribution, which has the same angular dependence and which appears due to the Ettingshausen effect. In order to clarify the problem of influence of the twins on the Hall drag coefficient, we discuss the possibility of separating these two contributions in the experiment.
Free and self-trapped excitons in rare-gas cryocrystals: coexistence and mixing of states
Authors: Fugol’ I. Ya. , Tarasova E. I.
Published: July 2002

The absorption spectra for rare-gas cryocrystals are calculated taking into account one-phonon scattering and multiphonon interaction of free excitons with local lattice vibrations. The possibility of coexistence of free and self-trapped excitons in nonequilibrium states above the bottom of the exciton band is discussed on the basis of a comparison of the free exciton energy with exciton damping in the one-phonon scattering and during transitions to exciton-vibron states. It is found that free exciton damping at low temperatures is mainly determined by one-phonon scattering in the entire exciton band only for xenon. In argon and krypton crystals, both types of damping make comparable contributions. The probability of transition of an exciton to self-trapped states in neon is so high that the existence of band excitations is unlikely.
Tunneling of nonequilibrium quasiparticles excited by x-ray quanta in a nonsymmetric superconducting tunnel detector
Authors: Andrianov V. A. , Kozin M. G. , Sergeev S. A. , Shpinel V. S. , Koshelets V. P. , Abramova I. V.
Published: July 2002

Pulse height distribution from nonsymmetric superconducting Nb/Al/AlOx/Nb tunnel junction irradiated by x-ray quanta emitted by a Fe55 source is studied. Signals of opposite polarity emerging as a result of absorption in different electrodes of the tunnel junction are observed at low bias voltages. This makes it possible to obtain amplitude spectra of essentially different shape for each electrode separately. The dependence of the maximum charge output on the bias voltage is analyzed. The diffusion coefficient, effective lifetime, and recombination probability for quasiparticles are obtained. It is found that the charge output increases with the magnetic field strength.
Effect of pressure on the phase diagrams and dynamic properties of easy-plane antiferromagnets
Authors: Mitsay Yu. N. , Fridman Yu. A. , Bairamaliyeva G. A. , Alexeev C. N.
Published: July 2002

Phase diagrams and dynamic properties of strongly anisotropic, easy-plane antiferromagnets in the presence of external pressure are studied. It is demonstrated that the phase with tensorial order parameter is possible in the system. Spectra of bound magnetoelastic waves are studied in the vicinity of the phase transition points.
Microscopic mechanism of the effect of composition and topological orders of metal glasses on plastic shear resistance
Authors: Bakai A. S. , Bengus V. Z. , Tabachnikova E. D. , Duhaj P.
Published: July 2002

Singularities (minima) in the critical stress of catastrophic plastic shear are observed in the course of variation of composition and topological orders in metal glasses Fe85−xCoxB15 (x=15, 17, 19, 21, 25, 30, 40, 50, 64 at. %) due to a change in the chemical composition. The minima are observed for x=21 and 40 at. %, which is close to the rational ratios 3:1 and 1:1 of atomic concentrations of Fe and Co, that are regarded as stoichiometric ratios for the formation of nanoclusters with a high average binding energy. The change in the atomic structure of cluster boundaries is considered as a microscopic mechanism of the effect of composition and topological orders on the resistance to plastic shear. The difference in the concentrations of coinciding sites at cluster boundaries is estimated for metal glasses of stoichiometric and nonstoichiometric compositions.
Dynamics of small-angle domain walls in external oscillating magnetic field
Authors: Primak K. I. , Sukstanskiı̆ A. L.
Published: July 2002

The dynamics of small-angle domain walls existing in an easy-axis ferromagnet in the vicinity of spin-reorientation phase transition in an external in-plane magnetic field is studied. The dependence of the drift velocity on the amplitude, frequency, and polarization of the oscillating field is obtained.
Nonstationary effects in NbSe3 intercalated with hydrogen
Authors: Chashka Kh. B. , Bichko V. A. , Obolenskii M. A. , Hasan Raid , Beletskii V. I.
Published: July 2002

Temperature dependences of resistivity and current-voltage characteristics of NbSe3 single crystals intercalated with hydrogen are investigated in the temperature range 90–300 K in the normal state and in a state with a charge density wave near the first phase transition at 145 K. A state with nonlinear conductivity at T>145 K, IVC with a negative differential resistance, and low-frequency voltage oscillations in the state with the CDW are discovered. The results are interpreted on the basis of concepts of redistribution of intercalated hydrogen under the action of temperature diffusion and electric field during the propagation of a charge density wave.
Two-gap superfluidity in the theory of a Fermi liquid
Authors: Akhiezer A. I. , Isaev A. A. , Peletminsky S. V. , Yatsenko A. A.
Published: July 2002

The possibility of a phase transition from the one-gap superfluid state with the singlet or triplet pairing of fermions to the two-gap superfluid state corresponding to the superposition of states with the singlet and triplet pairing in a Fermi liquid is considered. The thermodynamic stability of new two-gap solutions is analyzed.
Theory for normal state critical Kapitza resistance of He4
Authors: Ferrell R. A. , Bhattacharjee J. K. , Mukhin S. I.
Published: July 2002

We study a steady state, bearing a heat current, Q0. In the normal state of liquid He4 with constraining geometry, near the lambda point, at temperatures T greater than the lambda temperature, Tλ. Critical order parameter fluctuations near the boundary are incorporated in the expression for the non-local thermal resistivity. The Kapitza resistance is manifested by the additional temperature rise at the boundary, as compared with the bulk-extrapolated value. Sensitivity of the calculations to the application of the Dirichlet boundary condition is discussed.
Bose–Einstein condensation and heat capacity of a nonideal gas
Authors: Yarunin V. S.
Published: July 2002

The theory of a nonideal gas developed by N. N. Bogoliubov is applied for a semiclassical description of nonlinear dynamics of Bose condensate density. Analytical calculations lead to temperature dependence of heat capacity Cv typical of superfluid He4 at temperatures below and above the superconducting transition temperature Tc except for the interval 1.6 K<T<2.2 K.
Effect of boson peak on low-temperature electron spin–lattice relaxation in amorphous materials
Authors: Giorgadze N. P. , Zakharov L. Zh.
Published: July 2002

The effect of a boson peak (BP) on the low-temperature electron spin–lattice relaxation in amorphous materials is investigated. It is shown that the contribution of the boson peak to one-phonon relaxation for EPR frequencies within the boson peak width dominates over the Debye contribution, and the field dependence of relaxation rate changes qualitatively, while the temperature dependence remains unchanged.
Peculiarities of vortex state of Bi-2212 single crystals
Authors: Sergeeva G. G.
Published: July 2002

A phase diagram of the vortex state of Bi-2212 single crystals in a magnetic field parallel to the ĉ-axis proposed under the assumption on the two-stage destruction of long-range vortex correlation in such crystals matches with the experimental results obtained by using different methods.Reference 1Reference 2Reference 3Reference 4Reference 5Reference 6Reference 7 The intersection of the dimensional crossover line Bcr(T) with the line corresponding to violation of long-range vortex correlations in the (ab∧)-plane makes it possible to explain the discontinuity at the critical point of the vortex lattice melting curve Tm(B). Possibilities of experimental investigation of low-temperature condensed state for B>Bcr and the temperature dependence Bcr(T) are considered.
Electrical properties of a normal contact to HTSC Josephson media
Authors: Omelchenko V. I. , Sukhanov A. A.
Published: July 2002

Electrical properties of normal metal contacts to percolation Josephson HTSC systems are studied by computer simulation. The current and voltage distributions, current–voltage characteristics (IVC), and temperature dependences Rc(T) of the resistance of the Josephson network with a limited contact are calculated. It is shown that macroheterogeneity of current distribution leads to broadening of the IVC and Rc(T) dependences of the contact in comparison with the bulk characteristics. In the vicinity of critical currents and temperatures, the contact IVC and Rc(T) obey the “3/2” law. A peak on the current and temperature dependences of the spreading resistance is observed. The applicability of the effective medium model for describing contact characteristics of the Josephson network is substantiated. The computer simulation results are in accord with experimental temperature dependences of the contact resistance.
Backward helical waves in spatially disordered magnetic media
Authors: Ivanchenko E. A.
Published: July 2002

A nonlinear evolution system of hydrodynamic-type equations describing a three-dimensional multisublattice magnet is studied. An explicit expression is obtained for the energy density function of magnetic systems whose energy density is invariant to right- and left-spin rotations. Exact solutions for spin density are obtained in the form of helical waves for quadratic–biquadratic dependence of the energy density (in terms of Cartan’s invariant functions) in three-dimensional case. Solutions are also obtained for magnon fields inducing such waves. The existence of backward helical waves is predicted.
Evolution of oscillations of semiconfined electron plasma
Authors: Falko V. L. , Khankina S. I. , Yakovenko V. M.
Published: July 2002

The evolution of an arbitrary initial nonequilibrium distribution of electrons and electric fields is investigated in a structure consisting of semiconfined media, viz., plasma and insulator (vacuum). The comprehensive spectrum of potential oscillations of electric fields is obtained. It is shown that the set of frequency eigenvalues is determined by the properties of the electron distribution function in equilibrium and perturbed states. In a cold plasma, volume and surface oscillations with the Langmuir frequency can propagate along with surface plasmons, while only a surface plasmon field exists in the insulator. In the presence of spatial dispersion, all types of volume and surface oscillations emerging in the plasma are emitted to the insulator. In addition to the field of intrinsic oscillations, an electric field of anomalous penetration associated with the effects of ballistic transport of conduction electrons at low temperatures also exists in the plasma. For a cold plasma, delay effects are taken into account, and the spatial and time distributions of the fields in the insulator are found.
The emergence of resistive state in the Meissner phase of superconductors upon an increase in temperature below the critical point
Authors: Brandt N. B. , Mironova G. A. , Rzhevskii V. V.
Published: July 2002

It is shown that the resistive state emerging upon an increase in temperature in the region below the critical point in the Meissner phase of superconductors can be detected by measuring the variation of the frozen magnetic field in a mesoscopic hollow cylindrical sample upon its heating in the superconducting state. Owing to magnetic flux quantization, the decrease in the magnetic field upon heating must be step-wise.
Quantum levels and quasi-local states of SINIS structures
Authors: Gogadze G. A. , Kosevich A. M.
Published: July 2002

Quantum states of a superconductor–insulator–normal metal–insulator–superconductor sandwich (the SINIS structure) are investigated on the basis of the Bogoliubov–de Gennes equations. The dispersion equation is obtained for the quasiparticle spectrum for energies E<Δ (Δ is the energy gap in the superconductor) taking into account the Andreev scattering as well as conventional electron reflection at the interfaces of the SINIS structure. The spectrum makes it possible to calculate the Josephson current in the system. The transparency coefficient of the system for electrons with a continuous energy spectrum is calculated, and quasi-local states (“resonance levels” of transparency) are determined for the structure under investigation.
Low temperature spin-glass magnetic behavior of Ce3Pd20Ge6
Authors: Gaidukov Yu. P. , Nikiforov V. N. , Koksharov Yu. A. , Szymczak R. , Szymczak H. , Gribanov A. V.
Published: July 2002

A polycrystalline sample of Ce3Pd20Ge6 is investigated using a dc SQUID magnetometer. A noticeable difference between ZFC and FC magnetic susceptibility is found below ≈60 K. The temperature dependence of the magnetic susceptibility demonstrates an anomaly near approximately 2.8 K below which a remanent magnetic moment exists. Two characteristic temperatures detected support the assumption that there are different cerium magnetic subsystems in Ce3Pd20X6 (X=Ge, Si) compounds. Unusual magnetic behavior observed in Ce3Pd20Ge6 is discussed within the framework of the “molecular magnetism” model which predicts a frustration of exchange interactions.
Mixed state stability range in a YBaCuO single crystal
Authors: Kugel’ K. I. , Rakhmanov A. L. , Mamsurova L. G. , Pigal’skiı̆ K. S.
Published: July 2002

The range of applied magnetic field H corresponding to the stability of mixed state with a fixed magnetic induction B is determined for a high-Tc superconducting YBa2Cu3Ox single crystal for H⊥c-axis. For this purpose, the field dependences of the contribution μv to the dynamic magnetic permeability μac′ are analyzed for the hysteresis loops μv(H) in the temperature range from 70 to 84 K. It is shown that the μv(H) hysteresis can be interpreted in terms of the interaction between the vortex lattice and the surface and is associated with the B(H) hysteresis as a manifestation of the Bean–Livingston surface barrier. As a result, the μv(H) hysteresis loops corresponding to different temperatures can be described by a universal curve in dimensionless coordinates. The obtained estimates and the available experimental data reveal a significant suppression of the surface barrier in actual YBaCuO single crystals as compared to the barrier predicted for a perfect surface. The lower branch of the μv(H) hysteresis loop, which corresponds to increasing H, is found to be close to the equilibrium μv(H) curve, and the surface barrier appreciably affects the behavior of μv(H) only for decreasing field, i.e., the emergence of magnetic vortices from the sample surface.
Recombination of charge carriers in neon cryocrystals containing oxygen impurity
Authors: Belov A. G.
Published: July 2002

The recombination of electrons and holes in neon crystals containing deep electron traps due to impurity oxygen along with weakly localized electron states of the matrix is investigated experimentally. Measurements are made by the method of cathode-luminescence spectroscopy in VUV, UV, and visible wavelength ranges at temperatures varying from 2 to 8 K. It is found that the temperature dependences of integral intensities of intrinsic and extrinsic luminescence in solid solutions of oxygen in neon are similar and nonmonotonic by nature. The observed effect is analyzed in the model of two coexisting channels of energy relaxation of electron excitations: through the Γ(1/2,3/2) exciton subsystem and through the recombination of self-trapped two-center holes and electrons. It is shown that temperature variations of integral parameters of luminescence are mainly due to peculiarities of the recombination channel whose efficiency is determined by the probability of electron localization in the matrix lattice in the low-temperature regions (2.5–5 K) and by the probability of trapping at impurity centers in the temperature range 6–8 K. Additional proofs are obtained for the possibility of electron self-trapping in the Ne lattice with the formation of shallow localized states.
Atomic structure of interfaces between amorphous and crystalline phases in tungsten
Authors: Bakaı̆ A. S. , Mikhaı̆lovskiı̆ I. M. , Sadanov E. V. , Mazilova T. I. , Lugovskaya E. I.
Published: July 2002

The atomic structure of the interfaces in amorphous–crystalline tungsten obtained in situ by ultrafast quenching to low temperatures from the liquid phase are investigated by the methods of field ion microscopy. A high degree of localization of imperfections and interfacial incoherence is established. The coordinates of atoms at interfaces correspond either to the crystalline or to the amorphous phase. Transition regions with intermediate positions of atoms were observed only in the vicinity of boundary regions between closely packed crystallographic planes and paraplanes.
Interaction of a quantum Hall system with waveguide elastic modes
Authors: Fil D. V.
Published: July 2002

The interaction of nonuniform plane elastic modes of the wave-guide type with monolayer and double-layer quantum Hall systems is considered. It is shown that in contrast to the case of propagation of surface acoustic waves, no restrictions are imposed for waveguide modes on the maximum values of wave vectors for which the value of the phase velocity shift of the wave can be observed experimentally. Fractional incompressible Hall states can be studied by using the effect for measuring the dependence of the effective magnetic length on the filling factor and for observing phase transitions in double-layer systems under the variation of the separation between the layers.
Long-period incommensurate structures in crystals with triangular arrangement of magnetic ions
Authors: Zavorotnev Yu. D. , Medvedeva L. I.
Published: July 2002

The possibility of formation of a long-period structure in crystals with triangular arrangement of magnetic atoms is considered. It is shown that two cycloid and one spiral structures are formed. The influence of a magnetic field and second-order magnetic crystallographic anisotropy is studied. Superstructures can be transformed into one another by turning the plane of irreducible vectors for which “anticentrifugal” effect takes place, and an intermediate structure called a “rotating skew spiral” (RS̃S̃) is formed. It is also shown that “domains” over whose length irreducible vectors turn through an angle of π/2 can emerge in the system. These “domains” can form structures with a jump in the phase of irreducible vectors at the boundary.
Deceleration of charged particles in a two-dimensional electron gas with impurity states of electrons
Authors: Ermolaev A. M. , Haghighi Babak
Published: July 2002

Differential cross-section of inelastic scattering and loss function of fast charged particles in a two-dimensional electron gas are calculated at low temperatures, taking into account the localization of electrons at impurity atoms. The contribution of one-particle and collective excitations of the electron gas to the scattering cross-section and loss function is considered. One-particle excitations are manifested in the existence of a threshold of scattering cross-section and loss function, associated with a transition of localized electrons to the conduction band. Localization of electrons leads to a decrease in the frequency of two-dimensional plasmons. Consequently, the plasma loss lines in the energy spectrum of electrons passing through a two-dimensional electron gas are displaced towards lower frequencies and are broadened. Numerical estimates are obtained for the inversion layer at the boundary between silicon and silicon dioxide.
De Haas–van Alphen effect and superconductivity
Authors: Gor’kov L. P.
Published: July 2002

The problem of the robust de Haas–van Alphen oscillations seen experimentally in mixed superconducting state is discussed. The new threshold mechanism is suggested to explain persistence of the quantum oscillations deep in the superconducting state.
The ground state of the “frozen” electron phase in two-dimensional narrow-band conductors with a long-range interelectron repulsion. Stripe formation and effective lowering of dimension
Authors: Slutskin A. A. , Slavin V. V. , Kovtun H. A.
Published: July 2002

In narrow-band conductors a weakly screened Coulomb interelectron repulsion can supress narrow-band electrons’ hopping, resulting in formation of a “frozen” electron phase which differs principally from any known macroscopic self-localized electron state including the Wigner crystal. In a zero-band-width limit the “frozen” electron phase is a classical lattice system with a long-range interparticle repulsion. The ground state of such systems has been considered in the case of two dimensions for an isotropic pair potential of the mutual particle repulsion. It has been shown that particle ordering into stripes and effective lowering of dimension resides universally in the ground state for any physically reasonable pair potential and for any geometry of the conductor lattice. On the basis of this fact a rigorous general procedure for describing the ground state fully has been formulated. Arguments have been adduced that charge ordering into stripes in high-Tc superconductors testifies to the presence of a “frozen” electron phase in these systems.
Cooper instability in the occupation dependent hopping Hamiltonians
Authors: Boyaci H. , Kulik I. O.
Published: July 2002

A generic Hamiltonian, which incorporates the effect of the orbital contraction on the hopping amplitude between nearest sites, is studied both analytically at the weak coupling limit and numerically at the intermediate and strong coupling regimes for a finite atomic cluster. The effect of the orbital contraction due to hole localization at atomic sites is specified with two coupling parameters V and W (multiplicative and additive contraction terms). The singularity of the vertex part of the two-particle Green’s function determines the critical temperature Tc and the relaxation rate Γ(T) of the order parameter at temperature above Tc. Unlike the case in conventional BCS superconductors, Γ has a non-zero imaginary part which may influence the fluctuation conductivity of the superconductor above Tc. We compute the ground state energy as a function of the particle number and magnetic flux through the cluster, and show the existence of the parity gap Δ appearing at the range of system parameters consistent with the appearance of the Cooper instability. Numeric calculation of the Hubbard model (with U>0) at arbitrary occupation does not show any sign of superconductivity in a small cluster.
Raman scattering and phase transitions in mixed crystals K1−x(NH4)xH2PO4
Authors: Popkov Yu. A. , Van’kevich A. V. , Taranova I. A. , Savchenko E. M. , Shuvalov L. A.
Published: July 2002

Spectral parameters of the Raman scattering band corresponding to intrinsic vibration ν2(A1) of the PO4 tetrahedron in mixed crystals of K1−xAxDP with various ammonium concentrations are studied in the temperature range 4.2–300 K. Abrupt changes in frequency and half-width of the band are observed during transitions to ordered ferroelectric (x=0.00, 0.02, 0.04, 0.08) or antiferroelectric (x=0.74,0.82) phases. The decrease in the band half-width during ordering indicates the participation of excitations responsible for the corresponding states in relaxation processes. The transition to the structural glass phase (x=0.22, 0.32, 0.53) is not accompanied with sharp changes in the band parameters, but the band half-width at low temperatures is smaller than the expected value for totally disordered paraelectric phase.
Nonlinear resonant tunneling through doubly degenerate local state and strong electron-phonon interaction
Authors: Ermakov V. N.
Published: July 2002

In an approach of low transparency of the barrier the tunneling of electrons through doubly degenerate local state has been considered with allowance for the Coulomb and electron-phonon interactions. It is shown that in the case of weak electron-phonon and strong electron-electron interactions the dependence of tunneling current on the applied voltage has a step-like character at low temperature. The threshold value of the current was measured for small applied bias. The bistable state of the tunneling current is possible in the region of large bias. In the case of strong electron-phonon and weak electron-electron interactions, the threshold of tunneling current can be bistable. This result is a direct consequence of the electron pairing in local states.
Amplitude–phase spectroscopy of resonant reflection of light by crystals with a Fabry–Perot interferometer at the surface
Authors: Kosoboutski P. S.
Published: July 2002

Conditions for the formation of the minima of amplitude spectra of reflection of electromagnetic waves by transparent Fabry–Perot interferometers fixed on crystal surfaces with resonant dispersion of the dielectric constant ε̃(ω) are investigated. It is shown that, irrespective of the nature of the dispersion ε̃(ω), the minimum of the reflection contour is formed at a frequency ωm of phase compensation, for which the general phase of the reflected wave is a multiple of π. Analytic expressions connecting the frequency corresponding to the minimum of the reflection contour with parameters of the surface resonator and resonant excitation of bulk excitons, phonons and plasmons in the substrate are obtained.
Rectification of surface polaritons in an insulator in a magnetic field at the boundary with a metal
Authors: Chupis I. E. , Mamaluy D. A.
Published: July 2002

Surface polaritons in a semi-infinite insulator in a constant magnetic field at the boundary with an ideal metal or a superconductor have been considered. These polaritons are induced by dynamic magnetoelectric interaction, which exists in any insulator in the presence of a magnetic field. The modes of these surface polaritons differ appreciably in opposite directions of the magnetic field or the propagation of the wave. As a result, polaritons of the given optical or IR frequency propagate only in one direction, which is the effect of rectification of surface electromagnetic waves. The inversion of the magnetic field results in “switching on” or “switching off” of surface polaritons.
Generation of nonequilibrium phonons in Bi in a quantizing magnetic field
Authors: Bogod Yu. A.
Published: July 2002

The voltage across a Bi single crystal in the [E×H] direction (transverse voltage E⊥) is investigated in strong crossed electric E and magnetic H fields under phonon generation conditions. Information on electron acousto-emf Eea of bismuth, forming segments with a negative differential conductivity on current–voltage characteristics j vs. E⊥, is obtained. Acousto-emf is measured as the absolute value of the difference in transverse voltage before and after the transition of the sample to the phonon generation mode. It is found that the dependence of acousto-emf on quantizing magnetic field is nonmonotonic. This is associated with oscillations in the electron–phonon generation rate ∂Nq/∂t in a magnetic field, i.e., with oscillations of the phonon–electron collision frequency τpe−1.
Magnetic phase transition and magnetoresistive effect in Nd0.6Ca0.4(Mn1−xMex)O3 (Me=Cr, Al, Ti, Nb)
Authors: Troyanchuk I. O. , Efimov D. A. , Eremenko V. V. , Sirenko V. A. , Shimchak G. , Nabyalek A.
Published: July 2002

The properties of Nd0.6Ca0.4(Mn1−xMex)O3 (Me = Cr3+, Al3+, Ti4+, Nb5+) are investigated. It is shown that the indicated substitutions destroy the long-range order in the positions of the Mn3+ and Mn4+ ions, but the properties depend sharply on the type of substituent ion. The replacement of a small fraction of the Mn3+ ions by Cr3+ (0.04⩽x⩽0.1) leads to antiferromagnet–ferromagnet and insulator–metal transitions. At chromium concentrations x⩾0.1 the solid solutions again become nonconducting and exhibit the properties of inhomogeneous ferrimagnets in which the magnetic moments of the chromium and manganese ions are directed opposite to each other. For T<30 K there is a phase transition in which the magnetic moments of the Nd3+ ions order antiparallel to the moments of the Mn ions. All of the samples containing chromium have a large magnetoresistive effect at temperatures below the Curie point. The replacement of manganese by Al3+, Ti4+, or Nb5+ ions leads to a transition from the antiferromagnetic state to a spin glass state with no change in conductivity. The data obtained indicate that the superexchange interactions between the chromium and manganese ions is of an antiferromagnetic character.