bluuebunny/crossref_metadata_2025 huggingface dataset:
KdV extensions with Painlevé property
Authors: Lou Sen-yue
Published: July 2002

By means of the conformal invariance (Möbious transformation invariance), the well known KdV equation is extended to (i) a (1+1)-dimensional space-time symmetric form; (ii) two (2+1)-dimensional space isotropic forms; and (iii) general (3+1)-dimensional and N-dimensional forms. The extensions are proven to be integrable under the meaning that they possess the Painlevé property.
Derivative expansion of the effective action for quantum electrodynamics in 2+1 and 3+1 dimensions
Authors: Gusynin V. P. , Shovkovy I. A.
Published: July 2002

The derivative expansion of the one-loop effective action in QED3 and QED4 (quantum electrodynamics) is considered. The first term in such an expansion is the effective action for a constant electromagnetic field. An explicit expression for the next term containing two derivatives of the field strength Fμν, but exact in the magnitude of the field strength, is obtained. The general results for both fermion and scalar electrodynamics are presented. The cases of pure electric and pure magnetic external fields are considered in detail. The Feynman technique for the perturbative expansion of the one-loop effective action in the number of derivatives is developed.
Localized vibration spectra of crystals with intercalated plane
Authors: Ivanov M. A. , Skripnik Yu. V. , Gumenchuk N. N.
Published: July 2002

Additional symmetric and antisymmetric localized branches of the vibrational spectrum of a crystal, associated with the presence of intercalated (interstitial) planes in strongly anisotropic crystals, are investigated by using the discrete model and taking into account the interaction between nearest neighbors. Energy–momentum relations for such vibrations are analyzed, and the values of parameters for which local vibrations are excited above and below the energy band in the continuous spectrum of the crystal corresponding to the given value of the wave vector component in this plane are determined. Special attention is paid to an analysis of the possibility of formation of well-defined resonant modes of the spectrum, which are located within the allowed band and are polarized along and across the interstitial plane.
On corrections in the Ginzburg–Landau equations associated with the normal component flow in a superfluid Fermi liquid with triplet p-wave pairing
Authors: Tarasov A. N.
Published: July 2002

The Ginzburg–Landau (GL) equation is derived for the spatially inhomogeneous order parameter (OP) of the He3 type superfluid Fermi liquid (SFL) (composed of electrically neutral fermions with triplet p-wave pairing) for a uniform flow of the normal component of the SFL with a velocity vn≪2Tc/pF (Tc is the temperature of phase transition from the normal to the superfluid state, and pF is the Fermi momentum). The derivation is based on the integrodifferential equation for OP, which is valid at temperatures near Tc in the absence of strong-coupling effects. The main results are the corrections for the coefficients of the OP gradients in the GL equation (caused by the fact that vn≠0), which are calculated in the perturbation theory. These corrections, which indicate the deformation of the OP due to the SFL flow with the velocity vn, can be not only comparable for vn≪2Tc/pF, but also greater than the so-called nontrivial strong-coupling corrections to these coefficients, depending on the value of vn, and hence can be of practical importance for describing He–B3 at low pressures, when the strong-coupling effects are weak.
Positive Hall effect in a transition-metal-free amorphous alloy
Authors: Kuźmenko V. M. , Melńikov V. I.
Published: July 2002

The Hall effect of homogeneous amorphous Be films of thickness 25–100 nm stabilized with hydrogen impurity is investigated at 10 K<T<50 K. The value of Hall coefficient estimated as RH=+(1.1±0.2)×10−10 m3/C is found to be independent of temperature and sample thickness. This is the first consistently repeatable observation of positive Hall effect in a homogeneous nontransition amorphous metal. The observed effect contradicts the predictions of the theory that the Hall effect in nontransition amorphous metals must be negative.
Superfluid He3 in the zero temperature limit (Review Article)
Authors: Pickett G. R.
Published: July 2002

In this paper we discuss some (and only a small fraction) of the interesting properties of superfluid 3He at the low-temperature limit. We concentrate on the unique behavior and applications of the very dilute excitation gas at the lowest temperatures. This gas has been used for among other things, the probing of the A–B phase interface, the detection of low-energy particle events and in the simulation of the creation of cosmic strings.
The properties of vacancies in solid He4 as studied by pressure measurements
Authors: Remeijer P. , Steel S. C. , Jochemsen R. , Frossati G. , Goodkind J. M.
Published: July 2002

The temperature dependence of the pressure at a constant volume in solid He4 in the low-density hcp phase has been measured. The measurements are analyzed in terms of a localized vacancy model and the free Bose gas model of vacancies in solid helium. The results agree better with the free Bose gas model. On the basis of this model the effective mass of the vacancies was determined to be 3–5 times the bare mass of a He4 atom, which corresponds to a bandwidth of 1.3–2.1 K.
Magnetization relaxation in superconducting fulleride K3C60 single crystals
Authors: Buntar V. A. , Sauerzopf F. M. , Weber H. W. , Buntar A. G. , Kumani H. , Haluska M.
Published: July 2002

Magnetic relaxation processes in superconducting fulleride K3C60 are investigated on monocrystalline samples in a wide range of temperatures and magnetic fields. A logarithmic time dependence M(t) of magnetization is observed in samples with 100% of superconducting phase. The normalized relaxation rate increases with temperature in the entire range of magnetic fields. The flux creep activation energy ranges from 10 to 80 meV, and its temperature dependence has a peak. It has been concluded from the results of measurements on samples with nonideal stoichiometry that inhomogeneities strongly affect the relaxation processes and can mask the logarithmic dependence M(t) completely.
Nonlinear microwave properties of epitaxial HTS films
Authors: Melkov G. A. , Malyshev V. Yu. , Korsak S. K.
Published: July 2002

The surface resistance Rs of epitaxial HTS films of YBa2Cu3O7−δ on sapphire is studied experimentally at a frequency of 8.95 GHz in the presence of an additional powerful microwave signal of frequency 9.4 GHz ensuring the ac magnetic field amplitude up to 20 Oe on the film. It is found that the surface resistance Rs of the HTS film increases with the amplitude of the additional signal. The value of Rs of the HTS film virtually coincides with the value of the nonlinear surface resistance of the film at the same amplitude of the ac magnetic field. In other words, the surface resistances of the film for a weak signal in the presence of an additional powerful signal and for the powerful signal alone are close. The observed phenomena are explained under the assumption that the HTS film is a Josephson medium containing various types of Josephson junctions. Under the influence of a powerful microwave signal, the properties of this medium can vary due to switching of a part of the junctions, causing a transition of the medium to a new state which is manifested identically both for a weak and for a powerful signal.
High-frequency spin susceptibility of a two-dimensional electron gas with electron impurity states
Authors: Gleizer N. V. , Ermolaev A. M. , Rudnev A. D.
Published: July 2002

The high-frequency asymptotic form of dynamic spin susceptibility of a two-dimensional electron gas is obtained. Local states of electrons in impurity atoms and the quantizing magnetic field are taken into consideration. The susceptibility has resonant singularities at frequencies of electron transitions between Landau levels and local levels. In the absence of a magnetic field, the real part of susceptibility has a logarithmic singularity while the imaginary part has a peak at the threshold frequency of bound electron activation by a variable magnetic field.
Interference phenomena and ballistic transport in a one-dimensional ring
Authors: Moskalets M. V.
Published: July 2002

The dependence of the conductance of a one-dimensional ballistic ring on a potential barrier at one of the branches of the ring is considered at a nonzero temperature. The case of a small potential barrier (Aharonov–Bohm electrostatic effect) as well as a tunnel barrier is considered. The possibility of direct measurement of the electron wave function phase variation upon tunneling is discussed.
Photoconductivity of a quantum ballistic contact
Authors: Borovikov V. S. , Gorelik L. Yu. , Kleı̆ner V. Z. , Shekhter R. I.
Published: July 2002

The electron transport through a microscopic constriction in a two-dimensional quantum channel in an alternating transverse electromagnetic field is considered. A general expression is derived for the photoconductivity as a function of elements of a multichannel scattering S-matrix. This expression generalizes the Landauer formula for the conductivity of a 2D ballistic point contact (BPC) to the case of inelastic processes of interaction of ballistic electrons with alternating electromagnetic field. The relation between the symmetry of the S-matrix of electrons and the transport properties of the BPC in a nonstationary field is considered. The photoconductivity of a BPC with an adiabatic geometry is obtained in the semiclassical approximation.
Noncentrality effects of impurity ions in an icosahedral environment
Authors: Roitsin A. B. , Artamonov L. V. , Klimov A. A.
Published: July 2002

The multivalley potential corresponding to the displacement of impurity ions from the center of symmetry to the centers of faces of icosahedrons, dodecahedron vertices, and centers of hexagonal faces of fullerenes is considered. The generalized effective Hamiltonian describing the behavior of endohedral complexes with noncentral ions in external electric fields of any orientation is derived. Its eigenvalues are obtained and line intensities of all possible transitions between tunnel levels are calculated. The paraelectric resonance spectrum is predicted and analyzed without an electric field as well as in the presence of a field.
Scattering theory of superconductive tunneling in quantum junctions
Authors: Shumeiko V. S. , Bratus E. N. , Wendin G.
Published: July 2002

A consistent theory of superconductive tunneling in single-mode junctions within a scattering formulation of Bogolyubov-de Gennes quantum mechanics is presented. The dc Josephson effect and the dc quasiparticle transport in the voltage-biased junctions are considered. Elastic quasiparticle scattering by the junction determines the equilibrium Josephson current. The origin of Andreev bound states in tunnel junctions and their role in equilibrium Josephson transport are discussed. In contrast, quasiparticle tunneling in voltage-biased junctions is determined by inelastic scattering. A general expression for inelastic scattering amplitudes is derived and the quasiparticle current is calculated at all voltages with emphasis on a discussion of the properties of subgap tunnel current and the nature of subharmonic gap structure.
Ultralow-temperature relaxation of far nuclei in solids via dipole reservoir of own nuclei of paramagnetic centers
Authors: Kostarov D. A. , Fokina N. P.
Published: July 2002

Abragam et al. (Physica B81, 245 (1976)) proposed a relaxation mechanism for far nuclei via dipole–dipole reservoir (DDR) of own nuclei of paramagnetic centers which do not “freeze” at ultra low temperatures. In order to verify the possibility of such a process, they proved that the matrix elements of flip-flops of own nuclei are the electron matrix elements due to the mixing of electron and nuclear spin states as a result of superfine interaction. This is equivalent to an increase in heat capacity (“increase in weight”) of the DDR of own nuclei. Such a “heavier” DDR subsequently plays the role of a thermodynamic subsystem through which far nuclei relax to the lattice, a narrow bottleneck being observed on the second relaxation region. Since this mechanism can play a dominating role in low-temperature nuclear relaxation as well as in other processes, it is important to obtain the Hamiltonian of a “heavier” DDR in explicit form, to calculate its heat capacity, and to estimate the effective relaxation rate of far nuclei via DDR, which has been accomplished in the present publication.
Vibrational modes of a terminated atomic chain
Authors: Glushko E. Ya. , Khrisanov V. A.
Published: July 2002

A complex terminated molecular chain adsorbed at the surface is analyzed without taking into account periodic boundary conditions and translational invariance approximation. The solution of the motion equation is a standing wave. The dispersion equation for band modes is obtained and conditions for the existence of localized states are investigated. The constructed parametric diagrams make it possible to evaluate vibrational bands and local modes (if they exist) for (SN)x and C-C samples. It is proposed that excitations of local and band modes of adsorbed molecules can be used for low temperature laser cleaning of the surface and for molecular engineering purposes.
Cooperative mechanism of diffusion in metal glass
Authors: Davydov L. N.
Published: July 2002

General relations for diffusion coefficients for the cooperative mechanism of diffusion are obtained on the basis of the proposed model of metal–metalloid glass. The thermodynamics of Bernal–Polk complexes is developed by using the Ising–Nakano Hamiltonian and the theory of frozen-in fluctuations. The temperature dependence of diffusivity is analyzed in the cases of large and small variance of pair interatomic correlations.
On the theory of low-temperature properties of spin systems with magnetic anisotropy
Authors: Zaslavskii O. B. , Ulyanov V. V. , Vasilevskaya Yu. V.
Published: July 2002

Temperature behavior of easy-axis paramagnets in a transverse magnetic field is considered. It is shown that the low-temperature susceptibility as a function of the field has a peak for all values of spin S. As the temperature increases from zero, this peak is first sharpened (and not blurred), its position changing nonmonotonically. For spins S<3, the peak becomes double-humped at a certain temperature, while for S⩾3, a flat-top peak is observed. Similar phenomena are also typical of biaxial paramagnets. The energy spectrum of the system coincides with 2S+1 low-lying energy levels for a particle moving in a potential field of a simple form, which has the shape of a double well for low magnetic fields. This makes it possible to calculate the tunneling velocity by using quantum-mechanical methods.
A new dynamic mechanism of topological charge creation in a commensurate one-dimensional charge density wave near the contact with a normal metal
Authors: Rozhavsky A. S. , Pershin Yu. V. , Kovalev A. S.
Published: July 2002

The dynamics of conversion of conduction electrons into topological solitons of a charge density wave (CDW) commensurability in an external electric field is investigated. A novel mechanism of initiation of a nonlinear CDW current in the vicinity of the interface between a CDW and a normal metal is revealed and explained. The nonlinear current is produced by the conduction solitons created by the moving profile of the order parameter, formed during the conversion of electrons into collective phase excitations of a CDW. The field dependence of the current is of threshold nature and has no analogs in the bulk mechanisms of CDW nonlinearity.
Contact conductivity oscillations of a 2D electron system in a magnetic field
Authors: Shikin V. B.
Published: July 2002

Peculiar conductivity oscillations of a 2D Corbino disk in a magnetic field in a magnetic field, which have been observed in recent experiments (V. T. Dolgopolov et al., Pis’ma Zh. Éksp. Teor. Fiz. 63b, 55 (1996) [JETP Lett. 63, 63 (1996)]), are considered on the basis of existing concepts concerning specific properties of contacts of a two-dimensional electron system with “external” metallic electrodes, which lead to violation of spatial uniformity of the 2D electron density.
The boundary resistance between superfluid He4 near Tλ and a solid surface
Authors: Fu Haiying , Baddar Hanan , Kuehn Kerry , Ahlers Guenter
Published: July 2002

We report high-resolution measurements of the singular contribution Rb to the thermal boundary resistance between a solid surface and superfluid helium near the superfluid-transition temperature Tλ. The results confirm the observation by Murphy and Meyer that a gap between the cell end and the sidewall leads to an apparent finite-current contribution to Rb. In the absence of such a gap, overall agreement of Rb with theoretical predictions is very good. Remaining small differences require further investigations. Without a sidewall gap and within our resolution we found no finite-current effects over the range 3.9 μW/cm2<Q<221 μW/cm2.
Helium flow in a confined region caused by heating under zero gravity: approaches based on molecular kinetics and mechanics of continuous media
Authors: Gorbunov A. A. , Polezhaev V. I. , Kryukov A. P. , Shishkova I. N.
Published: July 2002

Helium flow in an enclosure caused by sudden heating of the enclosure walls is considered. Boltzmann’s equation and complete time-dependent Navier–Stokes equations with appropriate boundary conditions are integrated numerically. It is shown that the results of calculations obtained by using these methods for a steady-state flow are close.
Autowaves of component concentration under directed crystallization
Authors: Gus’kov A. P.
Published: July 2002

The occurrence of autowaves at the interface as a result of a first-order phase transition had been examined. The linear analysis of a system of the equations for a liquid which contains two components shows that a phase transition at the interface can give rise to autowaves. A spectrum of these autowaves depends on parameters of the system. For a special case of the system parameters an analysis is made of the dependence of the spectrum of autowaves from a temperature gradient the interface. We show that as a result of a interface instability in the bulk solid phase there are various periodic structures of distribution of the component concentration. Surfaces of equal concentration for the spectra of the autowaves are built. A qualitative and quantitative comparison of the numerical calculations with experimental data is made.
Generalized surface nuclear spin wave induced by external magnetic field
Authors: Tarasenko S. V.
Published: July 2002

The two-sublattice model of an easy-axis antiferromagnet is used to show that an additional rhombic anisotropy induced by an external magnetic field can lead to the formation of a generalized nuclear spin wave near the surface of the magnet. The criterion for the existence of a generalized surface spin wave is formulated.
Peculiarities of electronic properties of δ〈Sb〉 layers in epitaxial silicon. IV. Hopping conductivity and nonlinear effects
Authors: Krasovitsky Vit. B. , Komnik Yu. F. , Mironov O. A. , Emeleus C. J. , Whall T. E.
Published: July 2002

The temperature dependence of the kinetic electronic characteristics (conductivity, magnetoresistance, Hall e.m.f.) is studied in the temperature interval 3–50 K on epitaxial silicon crystals having a δ 〈Sb〉 layer with sheet concentrations of Sb atoms 1×1013 and 5×1012 cm−2. The shape of the current–voltage characteristics is determined at various temperatures. It is found that the low-temperature kinetic phenomena in these objects are governed by the hopping mechanism of conductivity. A variable range hopping conductivity is observed at sufficiently low temperatures (<10 K). The nonlinearity of the current–voltage characteristics is explained by the theory of non-Ohmic hopping conductivity in moderately strong electric fields.
Magnetic-field suppression of superconductivity in layered high-Tc materials
Authors: Varyukhin V. N. , Levchenko G. G. , Medvedev Yu. V. , Pashchenko A. V. , Lewandowski S. J.
Published: July 2002

The dependence of the superconducting transition temperature in GdBa2Cu3O6+δ single crystals on the magnetic field H applied parallel to the intercrystalline layers is studied experimentally. A nontrivial dependence of the superconducting transition temperature on the field H is explained by magnetic field penetration into high-Tc single crystals. The presence of a layered structure leads to the formation of a spatially periodic magnetic structure with a period varying discretely in fields H≫Hc1 (Hc1 is the lower critical field). Any change in the magnetic structure results in a nonmonotonic (jumpwise) dependence of the superconducting transition temperature on the field H. The effect is estimated numerically by using the results of calculation of the critical temperature of small samples in strong magnetic fields.
Point contact studies of the superconducting gap of CeRu2
Authors: Naidyuk Yu. G. , Moskalenko A. V. , Yanson I. K. , Geibel C.
Published: July 2002

The measured dV/dI(V) curves of point contacts between the intermetallic compound CeRu2 in the superconducting state and the normal metal Cu correspond fairly well to the Blonder–Tinkham–Klapwijk model. It is used to obtain temperature and magnetic field dependence of the superconducting gap Δ. The Δ(T) dependence corresponds well to the BCS theory with 2Δ(0)/kBTc*=3.1±0.1. Additionally, a region of gapless superconductivity between Tc*≃4.4−5.4 K and Tcbulk≃6.2 K is found. The gap decreases approximately linearly in a magnetic field and vanishes in a field Bc*≃3.5 T, which is well below the upper critical field Bc2≃6 T and close to the irreversibility field.
Influence of pulsed electric current on the structure and superconducting properties of high-temperature superconductors
Authors: Raitchenko A. I. , Flis A. A. , Chernenko L. I. , Kryuchkova N. I.
Published: July 2002

The influence of high-density current pulses on the structure and superconducting properties of HTSC ceramics YBa2Cu3Ox is studied at room temperature. A gradual increase in the pulsed current density causes appreciable structural changes: when a certain threshold value is reached, the melting of large grains occurs and is accompanied by partial breaking of intergranular contacts resulting in degradation of superconductivity. A further increase in the current density leads to the recovery of superconducting properties, which is probably due to the formation of superconducting bridges between grains aligned along the current flow. The superconducting transition temperature remains unchanged in such samples, but subsequent thermal treatment leads to an increase in the superconducting transition temperature.
Effect of impurity barriers on low-temperature anomalies in plasticity parameters of β-Sn
Authors: Diulin A. N. , Kirichenko G. I. , Natsik V. D. , Soldatov V. P.
Published: July 2002

Plastic deformation determined by the slip of (100)〈010〉 screw dislocations in single crystals of β-Sn solid solutions with different concentrations of Cd, In, and Zn impurities is studied in the temperature range 1.6–150 K. Low-temperature anomalies of the yield stress τ0 and activation volume γ (kinks in the temperature dependence of τ0(T) and peaks on the stress dependence of the activation volume γ(τ)) are observed. The parameters of anomalies are found to be determined to a considerable extent by the concentration of impurity atoms in the alloy and by the height of the barriers formed by impurity atoms for dislocations. The observed effects are compared with the predictions of the theory describing the influence of impurities on the motion of dislocations through Peierls barriers of complex shape. The results of analysis of experimental data are in agreement with the assumption concerning the two-hump shape of the lattice potential relief in the (100)〈010〉 slip system.
Giant oscillations of the sound attenuation decrement in organic conductors in a magnetic field
Authors: Kirichenko O. V. , Peschansky V. G.
Published: July 2002

Attenuation of sound wave energy in low-dimensional organic conductors with several charge carrier groups is investigated theoretically. It is shown that the existence of a Fermi surface sheet in the form of a corrugated plane affects considerably the behavior of the sound attenuation rate Γ in a magnetic field H. Giant oscillations of Γ as a function of 1/H, which are not associated with quantization of charge carrier energy, are predicted. Oscillations with a period dependent on the wavelength of sound appear in a quantizing magnetic field in addition to the oscillations described by the Lifshitz–Kosevich formula.
Broken symmetry phase transition in solid HD: a manifestation of quantum orientational melting
Authors: Freiman Yu. A. , Tretyak S. M. , Jeżowski A. , Hemley R. J.
Published: July 2002

Theoretical study of the broken symmetry phase (BSP) transition line in solid HD reveals that its anomalous features provide evidence for quantum orientational melting. The observations of unusual reentrant behavior is a consequence of the symmetry properties of the system, namely, the fact that in HD all rotational states and transitions between them are allowed, in contrast to the behavior of the homonuclear isotopes H2 and D2. The systematic underestimation of the transition pressure characteristic of all theories of the BSP transition can be removed if crystal-field effects are taken into account.
Low-temperature properties of uniaxial paramagnets in a tilted magnetic field
Authors: Zaslavskii O. B. , Ulyanov V. V. , Vasilevskaya Yu. V.
Published: July 2002

The behavior of uniaxial paramagnets in a tilted magnetic field is considered as a function of temperature. The structure of the energy spectrum as well as magnetization and susceptibility components are determined. Exact formulas for the spin S=1/2 are obtained. Thermodynamic parameters of the system are studied for arbitrary values of S in an easy-axis and easy-plane cases in different approximations (weak and strong magnetic fields, low and ultralow temperatures, etc.). It is shown that in the easy-plane case, the transverse magnetization and longitudinal susceptibility as functions of magnetic field at low temperatures exhibit peculiarities in the form of a series of sharp spikes, while the longitudinal components of these quantities in the easy-axis case display only a single spike.
New size effects in the conductivity of metal–insulator–metal tunnel junctions
Authors: Svistunov V. M. , Khachaturov A. I. , Chernyak O. I. , Aoki R.
Published: July 2002

A simple theory that makes it possible to calculate the characteristics of metal–insulator–thin metal film tunnel junctions is developed. Along with the well-known oscillations in the voltage dependence σ(V) of tunneling conductance due to commensurate states, it predicts a number of new effects. For example, even in the case of a symmetric tunnel junction formed by the identical materials with a rectangular potential barrier, the σ(V) curve displays a noticeable asymmetry. The branch of the σ(V) curve corresponding to tunneling to the thin-film electrode contains a structure consisting of conductance dips.
On the dielectric constant anomaly in the antiferromagnetic phase of YMnO3
Authors: Chupis I. E.
Published: July 2002

It is proposed that the triangular antiferromagnetic β-structure precedes the triangular antiferromagnetic α-structure observed in YMnO3 by neutron diffraction studies at 4.2 K. The experimental observation of the anomalous behavior of the dielectric constant below Néel temperature is attributed to the phase transition between β and α configurations.
Acoustically stimulated phase transition and low temperature optical spectra in PbI2 crystal
Authors: Bilyi M. M. , Gorban I. S. , Dmitruk I. M. , Salivonov I. M. , Ostrovskii I. V.
Published: July 2002

The influence of an intensive ultrasonic wave on the crystal structure of PbI2 was investigated. Acoustically stimulated phase transition have been observed for the first time.
Current-phase relation for a superconducting point contact with a tunneling barrier
Authors: Gogadze G. A.
Published: July 2002

The microscopic theory of the dc Josephson effect for a short clean superconducting point contact with a tunnel barrier is developed. The influence of the ordinary quasiparticle scattering on the nondiagonal potential Δ of the superconductor is studied. It is shown that such processes may be significant in high-Tc superconductors for the case of a barrier with high transmittance. The current-phase relation for a point contact at arbitrary temperatures is calculated.
Magnetic transformations in reentrant region of the x–T diagram of Li0.5Fe2.5−xGaxO4 spin-glass system
Authors: Efimova N. N. , Kufterina S. R. , Anders A. G. , Startsev S. V. , Gurevich A. M. , Eropkin V. N.
Published: July 2002

Reentrant spinels Li0.5Fe2.5−xGaxO4 with x=0.9 and 1.2 display peaks on the temperature dependences of heat capacity C at T1=13.4 K (x=0.9) and 14.2 K (x=1.2) respectively, which are typical of a first-order phase transition. This transition is identified with the transformation of the collinear ferrimagnetic structure into a noncollinear structure preceding on the temperature scale the state of ferrimagnetic spin glass existing in the temperature range 0 K⩽T⩽Tf, where transition temperatures Tf are 9 K (x=0.9) and 12 K (x=1.2).
Influence of dynamic magnetoelectric interaction on surface polaritons in ferroelectrics
Authors: Chupis I. E. , Mamaluy D. A.
Published: July 2002

The existence of additional transverse electric (TE) and magnetic (TM) surface polaritons formed as a result of high-frequency magnetoelectric interaction in a ferroelectric is predicted. The spectrum of the new type of surface polaritons is analyzed for transverse orientation of the electric polarization relative to the crystal surface. These polaritons are different in ferroelectric domains with opposite directions of spontaneous electric polarization. Thus, TE surface polaritons exist only in domains with electric polarization directed into the medium. Besides, magnetoelectric interaction induces effects like birefringence and anomalous dispersion of TM polaritons. Moreover, it is found that TM polaritons can exist in those types of ferroelectrics in which their existence was forbidden earlier. The same effects must also exist not only in ferroelectrics, but also in ordinary dielectrics in a constant electric field at right angles to the crystal surface. The above-mentioned asymmetry of the effects, including their switching on/off, must be observed upon a change in the direction of the applied electric field.
Magnetic flux locking in two weakly coupled superconducting rings
Authors: de Bruyn Ouboter R. , Omelyanchuk A. N. , Vol E. D.
Published: July 2002

We have analyzed the quantum interference effects in the macroscopic “superconducting molecule.” The composite system consists of two massive superconducting rings, each interrupted by a Josephson junction, which are at the same time weakly coupled with one another. The special case of coupling via the Josephson four-terminal junction is considered. The structure of the macroscopic quantum states in an applied magnetic field is calculated. It is shown that, depending on the values of the magnetic fluxes through each ring, the system displays two groups of states, the “orthostates” with both induced currents going in the same direction, and the “parastates” with the opposite currents and with the total induced flux locked to zero value. The transition to the flux locked state with changing of the total applied flux is sudden and is preserved in a certain interval which is determined by the difference of the fluxes applied through each ring. It makes the system sensitive to small gradients of the external magnetic field.
Time evolution of the density of vibrational states in the crystal lattice of the system La–Sr–Cu–O
Authors: Chirkov A. G. , Chudinov V. G.
Published: July 2002

The molecular dynamics method is used for studying the dynamic properties of the crystal lattice of La–Sr–Cu–O system. It is shown that the density of vibrational states of the system undergoes an evolution, viz., a periodic redistribution between (phonon and soliton) peaks. Such an effect is associated with nonlinear resonance processes in the system.
Flux vortex pinning in a thick Ba0.64K0.36BiOy film
Authors: Barilo S. N. , Gatalskaya V. I. , Shiryaev S. V. , Zhigunov D. I. , Kurochkin L. A. , Szymczak H. , Szymczak R. , Baran M.
Published: July 2002

The magnetic properties of a Ba1−xKxBiOy film (x=0.36) of thickness 18 μm are investigated. It is shown that the field dependences Jc(B) of critical currents at 5–20 K in fields above the peak-effect field Hp are correctly described in the collective pinning theory for a vortex lattice with a small bundle size.
Photocurrent generation in single electron tunneling transistors
Authors: Tageman Ola
Published: July 2002

A single-electron tunneling transistor (SET) with a non-equilibrium mode population in one of the leads is analyzed theoretically. We model transport through a dot coupled to a channel, both formed by gates from the two-dimensional electron gas of a GaAs/AlGaAs heterostructure. The non-equilibrium mode population, which is induced by coherent THz-pumping in the channel, produces empty states below the Fermi level for electrons to tunnel into. A photocurrent arises, which is periodically saw-tooth peaked with respect to the voltage on a central gate. For intense THz-fields the peaks display plateaus that reflect the energy dependence of the mode population. We also predict a high-gain Vin/Vout transfer-characteristic, similar to that of a current biased SET.
On vortex phase of systems with pairing of spatially separated electrons and holes
Authors: Shevchenko S. I. , Bezuglyı̆ V. A.
Published: July 2002

The possibility of the emergence of a macroscopic amount of planar vortices with identical circulation in systems with pairing of spatially separated electrons and holes was predicted by us recently [S. I. Shevchenko, Phys. Rev. B56, 10355 (1997); ibid. B57, 14809 (1998)]. In the present work, we consider a structure formed by planar vortices in a disk-shaped sample in a magnetic field whose two-dimensional divergence differs from zero. The total number of vortices and the energy of a system of vortices are determined as functions of the external magnetic field and the sample size. It is found that the energy of the vortex structure is proportional to the volume of the system, and hence a vortex state is a new thermodynamic phase of the investigated system (analogous to the Shubnikov phase in conventional superconductors).
Misfit dislocation superlattices in IV–VI multilayered compounds as zero-dimensional quantum boxes
Authors: Sipatov A. Yu.
Published: July 2002

Quantum dots can be generated by a new method based on the formation of misfit dislocations in a perfectly periodic array network during the epitaxial growth of IV–VI compound superlattices. Infrared photoluminescence spectra of IV–VI superlattices are measured at temperatures T=5–90 K. A large blue shift and temperature independent line positions and width were observed in PhSe–PbS/(001)KCl superlattices with a three-dimensional periodic arrays of misfit dislocations. It is supposed that these features are due to quantum dot luminescence.
Magnetic properties of periodic nonuniform spin-1/2XX chains in a random Lorentzian transverse field
Authors: Derzhko Oleg
Published: July 2002

Using continued fractions we examine the density of states, transverse magnetization and static transverse linear susceptibility of a few periodic nonuniform spin-1/2XX chains in a random Lorentzian transverse field.
Magnetic properties of conventional superconductors with columnar defects
Authors: Braverman Gregory M. , Gredeskul Sergey A. , Avishai Yshai
Published: July 2002

Equilibrium vortex configuration in conventional type II superconductors containing short-range columnar defects is investigated theoretically. In the bulk superconductor near the upper critical field Hc2 a single defect causes a strong local deformation of the vortex lattice which has C3 or C6 point symmetry. The vortices can collapse onto attractive defects, while in the case of repulsion the regions free of vortices appear near a defect. Increasing the applied magnetic field results in an abrupt change of the configuration of vortices related to the formation of multiquantum vortices and giving rise to reentering transitions between configurations with C3 or C6 symmetry. In the case of a small concentration of defects these transitions manifest themselves as jumps of magnetization and discontinuities of the magnetic susceptibility. Columnar defects also influence significantly the magnetic properties of a mesoscopic superconducting disc. They help the penetration of vortices into the sample, thereby decreasing the sample magnetization and reducing its upper critical field. Even the presence of weak defects splits a giant vortex state (usually appearing in a clean disc in the vicinity of the transition to a normal state) into a number of vortices with smaller topological charges. In a disc with a sufficient number of strong sufficently defects vortices are always placed onto defects. The presence of defects lead to the appearance of additional magnetization jumps related to the redistribution of vortices that are already present on the defects and not to the penetration of new vortices.
Nonquantum oscillations associated with the dynamics of an electron in superlattice
Authors: Kosevich A. M. , Wagner I. D.
Published: July 2002

Oscillations associated with the classical motion of a Bloch electron in a spatially periodic structure whose period considerably exceeds the atomic spacing are discussed. Such phenomena include the so-called Bloch oscillations, i.e., the vibrational motion of an electron in a constant uniform magnetic field, and the oscillatory dependence of magnetoresistance on a constant magnetic field, associated with the geometrical resonance at which the electron orbit diameter in the magnetic field is commensurate with the superlattice period.
Vortex lattice melting in layered HTSC in the field of defects
Authors: Gracheva M. E. , Kashurnikov V. A. , Nikitenko O. A. , Rudnev I. A.
Published: July 2002

The effect of defect potential on the melting temperature of the vortex lattice in a layered HTSC is investigated. It is found that an increase in the value of the defect potential leads to a shifting of the phase transition point to the critical temperature, thus increasing considerably the range of the intermediate phase “rotating lattice.”
High-frequency ohmic losses in beryllium and its alloy with aluminum
Authors: Prentslau N. N.
Published: July 2002

The surface resistance of Be of different purity and its alloy with Al⋅(50%Be–50%Al) is investigated in the temperature range 4.2–300 K in the frequency region 0–1010 Hz. It is shown that in the temperature interval (in the vicinity of 77 K) where beryllium is a dc hyperconductor, the surface resistance of pure beryllium and the alloy has the lowest value as compared to other metals including aluminum. The temperature dependence of the surface resistance of Be and its alloy is successfully described by classical formulas of electrodynamics.
Temperature dependence of resistance of Pr0.65Ca0.35MnO3 films prepared by pulsed laser deposition
Authors: Prokhorov V. G. , Kaminsky G. G. , Flis V. S. , Lee Young Pak
Published: July 2002

Temperature dependence of resistance of Pr0.65Ca0.35MnO3 thin films prepared by pulsed laser deposition method are studied in the temperature range 4.2–300 K. It is shown that an abrupt change in the temperature dependence of resistance is observed in the region of antiferromagnetic ordering temperature TN. The experimental data are analyzed in the framework of modern theoretical concepts concerning the transport mechanism and perovskite-like manganites.
Peculiarities of low-frequency excitation spectrum of CsDy1−xBix(MoO4)2
Authors: Kut’ko V. I. , Gerashchenko S. S. , Nedbailo N. Yu.
Published: July 2002

Low-frequency IR transmission spectra for a series of isostructural single crystals of CsDy1−xBix(MoO4)2 (x=0, 0.05, 0.1, 0.2, 0.3, 0.5, and 0.7) are measured at low temperatures (T≃6 K). It is found experimentally that absorption band broadening takes place in the Bi concentration range 0.2⩽x⩽0.6. The mechanism which may result in absorption spectrum blurring are considered.
Commensurability effect and lock-in transition in Mo/Si superconducting superlattices
Authors: Yuzephovich O. I. , Bomze Yu. V. , Mikhailov M. Yu. , Dmitrenko I. M. , Fogel N. Ya.
Published: July 2002

We report the first observation of the lock-in transition in artificial superconducting superlattices, which takes place in tilted magnetic fields. The measurements were carried out on the Mo/Si layered system. The temperature dependence of the critical angle for the trapping of the vortices in the orientation parallel to the layer planes is determined by the previously known resistive method and by a new method based on the effect of commensurability between the intervortex distance and the superlattice wavelength. The temperature dependences of the critical angle obtained by the two methods practically coincide. The experimental results are consistent with the theoretical predictions of Feinberg and Villard.
On the influence of higher invariants of the thermodynamic potential on the onset of long-period magnetic structures
Authors: Zavorotnev Yu. D. , Medvedeva L. I. , Stefanovskiı̆ E. P.
Published: July 2002

The formation of superstructures is considered with allowance for the biquadratic exchange interaction. It is shown that in this case the simultaneous coexistence of several long-period structures is possible, which can arise as a result of a first- or second-order phase transition.
Influence of a biquadratic interaction on the magnetic ordering in two-dimensional ferromagnets
Authors: Fridman Yu. A. , Spirin D. V.
Published: July 2002

The question of whether the long-range magnetic order in a two-dimensional ferromagnet can be stabilized by the inclusion of a biquadratic interaction is investigated. It is shown that the stabilization of the long-range magnetic order results from the presence of a magnetoelastic interaction. Certain types of spin configurations in the system under study are investigated for different relative sizes of the Heisenberg and biquadratic exchange constants.
Features of the luminescence kinetics of Pr3+ ions in the Y2SiO5 crystal
Authors: Malyukin Yu. V. , Borisov R. S. , Lebedenko A. N. , Leonyuk N. I. , Roth M.
Published: July 2002

A temperature-dependent change in the decay kinetics of the luminescence of Pr3+ impurity ions in the Y2SiO5 crystal is observed. On the basis of the deviation of the luminescence decay law from a single-exponential form and the presence of a characteristic rising front in the luminescence kinetics it is established that there is a temperature-dependent transfer of electronic excitation energy between two optical centers in the Y2SiO5 crystal.
Specific heat of crystalline TlIn1−xCexS2 (0⩽x⩽0.04)
Authors: Godzhaev É. M. , Mamedova S. I. , Nazarov A. M.
Published: July 2002

Research results on the specific heat of TlIn1−xCexS2 (0⩽x⩽0.04) crystals in the temperature range 4.2–300 K are presented. It is found that TlIn1−xCexS2 crystals have a second-order phase transition in the temperature interval 173.4–214 K, and the sharpness of the specific-heat peaks decreases gradually as cerium is substituted for indium in TlInS2.
Backward electromagnetic waves in a magnetically disordered dielectric
Authors: Ivanchenko E. A.
Published: July 2002

A nonlinear-evolution set of equations of the hydrodynamic type describing a magnet with a noncollinear arrangement of spins is investigated. An explicit expression invariant to right and left spin rotations is used for the energy density. The model under consideration can be interpreted as a continuum limit of a system of distributed symmetric tops. In the three-dimensional case exact solutions for the spin density are obtained in the form of helical waves for the quadratic–biquadratic energy density (in terms of Cartan’s invariant functions). Solutions are also obtained for the magnon fields inducing these waves. The existence of backward helical waves is predicted. Energy transport may occur at an angle greater than π/2 relative to the direction of the helical waves. The analytical dependences of the wave vector and of the frequency on the helical wave amplitude, magnetic susceptibility, rigidity, and other constants of the model are found. The predicted property would allow for the construction of backward wave generators based on the use of disordered magnetic materials. The backward electromagnetic waves in a layered disordered magnetodielectric are considered. The relationship between the parameters of electromagnetic waves of the (e) layer and of the (i) layer is obtained.
Single-phonon damping of polaritons in cryocrystals of inert elements
Authors: Goncharuk N. A. , Tarasova E. I.
Published: July 2002

The single-phonon damping of polaritons governs the most important characteristics of the relaxation processes of excitations in the region of the resonance energy ET. Here the single-phonon damping of polaritons by acoustical phonons is calculated in the deformation-potential approximation for the lowest excitons Γ(3/2) in Ar, Kr, and Xe cryocrystals. The results of a numerical calculation of the curves of the energy dependence of the damping Γ(E,T=const) at several temperatures spanning the free exciton existence region for each crystal are presented. Analytical expressions are obtained for Γ(E,T) at T=0 and T>2ℏks. A comparison with the data from the numerical calculation indicates that a linear temperature dependence Γ(E=const,T) holds over a wide temperature range, except at very low temperatures. It is shown that at temperatures above the critical point there exists a region of energies in the neighborhood of ET in which processes involving the absorption of phonons are dominant and prevent the relaxation of the polaritons down the dispersion curve. The width of this region is comparable to the maximum phonon energy and increases with increasing temperature.
Isothermal condensation on a plane surface
Authors: Loyalka S. K. , Hamoodi S. A. , Tompson R. V.
Published: July 2002

The half-space problem of isothermal condensation of a vapor diffusing through a background gas is considered. Accurate numerical results for the jump distance and density profile in the Knudsen layer for arbitrary mass ratio (background/vapor) are obtained via the use of the SN method. The results correspond to the assumption of rigid sphere molecular interaction, but the development is sufficiently general that results for other molecular force laws could also be obtained. Finally, a correlation for the jump coefficient as a function of the mass ratio is given.