bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of magnetic flux gradients in hard superconductors
Authors: Bruk V. V. , Eremenko V. V. , Makedonskaya N. I. , Shabakayeva Yu. A. , Sirenko V. A.
Published: July 2002

Analytical calculations of the transverse magnetostriction in a thin hard superconductor are presented in relation to the distributions of currents and fields within a superconducting specimen in a varied magnetic field. The approach is successfully tested on high-temperature superconductors. The flux distribution derived from magnetostriction measurements is in satisfactory agreement with that obtained from computer processing of magnetooptical images. The magnetic flux distribution below the irreversibility line of hard superconductors is derived from both original magnetization and magnetostriction measurements and image processing. Perfect consistency of the results is obtained for a family of high-temperature superconductors (La2−xSrxCuO4, Bi2Sr2CaCu2Ox, YBa2Cu3O7−δ).
Comparative study of current–voltage characteristics of Ni and Ni(Pt)-alloy silicided p+/n diodes
Authors: Chi D. Z. , Mangelinck D. , Lahiri S. K. , Lee P. S. , Pey K. L.
Published: July 2002

A comparative study of the I–V characteristics of p+/n diodes silicided with a pure Ni and Ni(Pt) alloy has been performed. Higher saturation currents as well as abnormal reverse I–V characteristics were observed for some of the diodes which were silicided with pure Ni at 700 °C while good I–V characteristics were observed for other diodes. Our results show that the forward current in the diodes with good I–V characteristics is dominated by electron diffusion in the p+ region. For diodes with higher saturation currents, it has been concluded that both forward and reverse currents in these diodes are dominated by the current following through Schottky contacts that are formed due to inadvertent penetration of NiSi spikes through the p+ region into n region. The formation of Schottky contact was not observed in diodes silicided with a Ni(Pt) alloy, providing a clear evidence of enhanced thermal stability of Pt containing NiSi.
Photoluminescence characteristics of ZnTe epilayers
Authors: Yu Young-Moon , Nam Sungun , Lee Ki-Seon , Choi Yong Dae , O Byungsung
Published: July 2002

High quality ZnTe epilayers have been grown on semi-insulating GaAs(100) substrates by hot-wall epitaxy, and the photoluminescence characteristics were investigated. The free exciton binding energy is found to be 12.7 meV and the free exciton reduced mass to be 0.095m0 from the clearly resolved excitonic peaks. From the temperature dependence of the free exciton line, the room temperature energy gap of ZnTe epilayer is found to be 2.278 eV. The longitudinal optical phonon energy from the resonance Raman shift is determined as 26.2 meV. The binding energy of the exciton bound to the neutral acceptor is found to be 4.9 meV. The temperature dependence of the bound exciton peak intensity is explained with a two-step thermal quenching mechanism. Deep level emissions such as donor–acceptor pair emission, Y-band, and oxygen-bound emission are also studied.
Ab initio ground potential energy surface (3A″) for the O(3P)+N2O reaction and kinetics study
Authors: González Miguel , Valero Rosendo , Sayós R.
Published: July 2002

An ab initio CASPT2//CASSCF study of the A″3 ground potential energy surface for the O(3P)+N2O(X 1Σ+) reaction has been performed, investigating the two predominant reactive channels. Symmetry breaking is reported for some of the structures. Rate constants are calculated by means of the transition state theory yielding values in almost quantitative agreement with experiment for the 2 NO(X 2Π) channel, but at variance with experiment for the N2(X 1Σg+)+O2(X 3Σg−) one. A preliminary study on the possible existence of surface crossings (3A″–1A′, A″3–1A″, and A″3–3A′ intersections) reveals that more efforts are warranted to fully explain the origin of this discrepancy.
Dynamics of nonlinear excitations in the Frenkel–Kontorova model with a double-barrier potential
Authors: Gorbach A. V. , Kovalev A. S. , Usatenko O. V.
Published: July 2002

A nonlinear elastic chain in an external periodic double-barrier potential (a generalized Frenkel–Kontorova model) is considered. Small-amplitude dynamical localized excitations whose parameters lie in and near the gap of the spectrum of linear waves—gap and near-gap solitons—are investigated.
Influence of twin boundaries on the phase state and vortex dynamics near the melting point in YBa2Cu3O7−δ single crystals
Authors: Bondarenko A. V. , Prodan A. A. , Obolenskiı̆ M. A. , Sivakov A. G.
Published: July 2002

It is found that at temperatures above the melting point of the vortex lattice Tm and below the temperature Tp corresponding to the onset of pinning on twin boundaries, the current–voltage (I–V) characteristics are linear at low values of the transport current J but are substantially nonlinear at large J. This behavior of the I–V characteristics is interpreted as the coexistence in the temperature region Tm<T<Tp of a pinned vortex lattice which is formed near the planes of the twin boundary at T<Tp and an unpinned vortex liquid far the planes of twin boundaries.
Hot-spot dynamics and deceleration-phase Rayleigh–Taylor instability of imploding inertial confinement fusion capsules
Authors: Betti R. , Umansky M. , Lobatchev V. , Goncharov V. N. , McCrory R. L.
Published: July 2002

A model for the deceleration phase of imploding inertial confinement fusion capsules is derived by solving the conservation equations for the hot spot. It is found that heat flux leaving the hot spot goes back in the form of internal energy and pdV work of the material ablated off the inner shell surface. Though the hot-spot temperature is reduced by the heat conduction losses, the hot-spot density increases due to the ablated material in such a way that the hot-spot pressure is approximately independent of heat conduction. For direct-drive National Ignition Facility-like capsules, the ablation velocity off the shell inner surface is of the order of tens μm/ns, the deceleration of the order of thousands μm/ns2, and the density-gradient scale length of the order a few μm. Using the well-established theory of the ablative Rayleigh–Taylor instability, it is shown that the growth rates of the deceleration phase instability are significantly reduced by the finite ablative flow and the unstable spectrum exhibits a cutoff for mode numbers of about l≈90.
Interparticle forces and lift on a particle attached to a solid boundary in suspension flow
Authors: Feng Zhi-Gang , Michaelides Efstathios E.
Published: July 2002

The lattice Boltzmann method is used to simulate the shear flow field around a stationary particle attached to a solid boundary. One or more freely flowing (suspended) particles are introduced in the flow and are allowed to move, subject to the gravity force and the induced hydrodynamic force. Periodic conditions on the side boundaries assure that the same number of particles always remains in the computational domain. The total force exerted on the stationary particle is computed during the whole simulation process and resolved as the drag and lift components. By comparing these components of the hydrodynamic force before and after the freely flowing particles are introduced in the flow field, we determine the effect of suspended particles on a stationary particle. The results show that, even in the absence of particle collisions, the hydrodynamic force developed on the stationary particle is significant enough to induce the resuspension process if this particle were free to move.
Magnetization dynamics of electron–impurity systems at paramagnetic resonance
Authors: Ivanchenko E. A.
Published: July 2002

The equation for the magnetization is obtained on the basis of the kinetic equation for an isotropic distribution function of electrons scattering on massive impurity centers in the presence of magnetic and electric fields. The analytical solution of the Cauchy problem for a given initial distribution of the magnetization under conditions of paramagnetic resonance is obtained. The exact solutions are found for magnetization dynamics in samples having the forms of an ellipsoid of revolution and a cylinder, as well. The influence of magnetic exchange on the surface of the cylinder (III boundary value problem) is taken into account. The dependence of the magnetization on the static electric field is exponentially decreasing with time, with an exponent proportional to the electric field squared times the diffusion coefficient. For a fixed instant of time the magnetization depends nonlocally on the magnitude and direction of the electric field. The estimated dynamic shift of the forced precession has a nonlocal and nonlinear dependence on the nonuniform distribution of the initial magnetization. This shift is estimated with boundary conditions taken into account and is caused by a field similar to the Suhl–Nakamura field in a paramagnetic medium. The dynamic shift of the free precession has only a nonlocal character. The time and space dependence of the internal field is obtained. All results are expressed in terms of the initial distribution of the magnetization without specifying its functional form and in terms of the propagation function, which depends on the shape of the sample. These results may be used for analysis of spin diffusion in natural and manmade materials and also in magnetometry.
Point-contact studies of the Kondo size effect in the alloys CuMn, CuCr, and AuFe in a magnetic field
Authors: Fisun V. V. , Yanson I. K. , van Ruitenbeek J. M. , Mydosh J. A.
Published: July 2002

The splitting of the Kondo peak on the differential resistance–voltage characteristic in a magnetic field is investigated in CuMn, CuCr, and AuFe point contacts of different diameter. Empirical formulas are obtained which can take into account the variation of the energy position of the maxima of the split Kondo peak, both in external and internal (the spin-glass state) magnetic fields, as a function of the temperature of the experiment and the Kondo temperature and also as the diameter of the contacts is decreased.
Reinforcement of pinning by surface magnetic microparticles in high-Tc superconductors
Authors: Togulev P. N. , Bazarov V. V. , Khaı̆bullin I. B. , Suleı̆manov N. M.
Published: July 2002

A reinforcement of pinning in high-Tc superconducting materials by surface magnetic microparticles obtained by ion implantation is observed. Measurements are made by the method of magnetically modulated microwave absorption. In single crystals of Bi2Sr2CaCu2O8 an ensemble of magnetic particles is formed directly in a subsurface layer of the superconductor by the implantation of Fe+ ions followed by annealing. In experiments with YBa2Cu3O7 the magnetic microparticles of iron were formed individually in SiO2 films which were then applied to the surface of a thin film of YBa2Cu3O7, and measurements were made on the composite structure. In both cases reinforcement of the pinning is observed. In the limits of the chosen implantation regimes the pinning effect becomes stronger with increasing fluence of implanted iron atoms.
A derived-data type for data analysis
Authors: Metcalf Michael
Published: July 2002

A frequent requirement in physics data analysis is the ability to form and manipulate histograms; this is done currently using calls to the HBOOK subroutine package. Could its interfaces and internal structure be improved by defining a histogram to be a Fortran 90 data type instead?
Concurrent simulation of neurons on multi-Transputer systems
Authors: Migliore M. , Ayala G. F. , Fornili S. L.
Published: July 2002

This paper reports on a concurrent approach to efficiently simulate neurons on multi-Transputer systems. The neurons are represented as a series of interconnected isopotential compartments modeled by lumped electrical components. The corresponding system of first-order ODEs is mapped onto processor arrays of various sizes. The concurrent OCCAM program can be easily adapted to different model equations or integration methods.
Defect luminescence in cerium-doped yttrium aluminum garnet
Authors: Rotman S. R. , Warde C.
Published: July 2002

The absorption and photoluminescence of lattice defects and of the cerium ion (Ce+3) in cerium-doped yttrium aluminum garnet have been measured after annealing single crystals of this material in various reducing atmospheres. The absorption in the 200–300-nm wavelength range is observed to decrease as the partial pressure of oxygen (PO2) in the annealing atmosphere decreases, while both the cerium emission at 550 nm and the lattice defect luminescence at 300 nm increases. The lattice defect emission appears to be associated with electrons located on oxygen vacancies.
Epitaxial growth of LiNbO3-LiTaO3 thin films on Al2O3
Authors: Kanata T. , Kobayashi Y. , Kubota K.
Published: July 2002

Epitaxial thin films of LiNbO3 and LiTaO3 were grown on sapphire substrates by the rf-magnetron sputtering method. Structural characterization was made by several spectroscopic measurements: x-ray diffraction, Raman scattering, and optical absorption. We obtained epitaxial thin films with lattice-mismatched strained layers, without misfit defects which are usually created at the interface. Impurity-ion (Nd3+ and Cr3+) doped films were also grown; these films had larger refractive indices than the pure films. Furthermore, the heteroepitaxial thin films of up to 10 alternating LiNbO3/LiTaO3 layers were successfully grown, and their periodic structures were studied by optical second-harmonic generation.
Stress and microstructure of sputter-deposited thin films: Molecular dynamics investigations
Authors: Müller Karl-Heinz
Published: July 2002

In magnetron sputter deposition the intrinsic mechanical stress of films of refractory metals passes a tensile stress maximum, decreases and then becomes compressive with decreasing working gas pressure. To elucidate the dependence of internal tensile stress on film growth and microstructure, a two-dimensional molecular dynamics simulation is employed. The evolving structure is determined at an atomic level and the stress is calculated as a function of the kinetic energy of adatoms and fast neutralized inert gas atoms which arrive at the film surface. These energies are dependent on the deposition geometry and the working gas pressure. The theoretical results are in qualitative agreement with experiment and reveal that the initial increase in tensile stress with increasing adatom and neutral incident kinetic energy is caused by a microstructural change from microcolumnar growth to a more densely packed atomic network with closed micropores. Interatomic attractive forces producing tensile stress can act most effectively in such a structure. The subsequent decrease in stress is attributed to a less defect-rich, better ordered absorbate structure formed at higher kinetic energies of arriving species. Stress is found to vary in a similar fashion as a function of incident kinetic energy for both sputtered atoms and fast neutrals. The compressive stress regime has not been investigated.
Temperature dependence of optical properties of GaAs
Authors: Yao Huade , Snyder Paul G. , Woollam John A.
Published: July 2002

Pseudodielectric functions 〈ε〉=〈ε1〉+i〈ε2〉 of GaAs were measured by spectroscopic ellipsometry (SE), in the range of 1.6–4.45 eV, at temperatures from room temperature (RT) to ∼610 °C. A very clean, smooth surface was obtained by first growing an epitaxial layer of GaAs on a GaAs substrate and immediately capping it with a protective layer of arsenic. The cap prevented surface oxidation during transport to the measurement chamber, where it was evaporated under ultrahigh vacuum at ∼350 °C. Room-temperature SE results from this surface are in good agreement with those in the literature obtained by wet-chemical etching. A quantitative analysis of the 〈ε〉 spectrum was made using the harmonic-oscillator approximation (HOA). It is shown by the HOA that the E1 and E1+Δ1 energy-band critical points shift downward ∼300 meV as temperature increases from RT to ∼610 °C. An algorithm was developed, using the measured optical constants at a number of fixed temperatures, to compute the dielectric function spectrum at an arbitrary temperature in the range of 22–610 °C. Therefore, the ellipsometer can be utilized as an optical thermometer to determine the sample surface temperature.
Optical properties of ZnTe
Authors: Sato Kohzo , Adachi Sadao
Published: July 2002

The optical response of ZnTe in the 1.5–5.6 eV photon energy range at room temperature has been studied by spectroscopic ellipsometry. The measured dielectric-function spectra reveal distinct structures at energies of the E0, E1, E1+Δ1, and E2 critical points. These data are analyzed on the basis of simplified model of the interband transitions. Results are in satisfactory agreement with the calculations over the entire range of the photon energies. Dielectric-related optical constants of ZnTe, such as the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity, are presented and analyzed. Results of surface-treatment effect on the pseudodielectric functions have also been presented.
Analysis of the vibrational mode spectra of amorphous SiO2 films
Authors: Martinet C. , Devine R. A. B.
Published: July 2002

The spectral line shapes and the absorption frequencies of the oxygen related infrared active vibrational modes in amorphous SiO2 are studied both experimentally and by simulation. Experimental data were obtained on oxides grown thermally in the temperature range from 800 to 1050 °C and on oxides deposited at 300 °C by plasma enhanced chemical deposition. The transverse optic (TO) mode centered around 1090 cm−1 is found to have a line shape and peak frequency which varies significantly with film thickness while the longitudinal optic (LO) mode at 1256 cm−1 is invariant. Data on both modes and on refractive index is used to demonstrate consistently that the 800 °C grown oxide is 1.6%–2.0% denser than that grown at 1050 °C. For thin oxides (<10 nm) there is evidence from both TO and LO modes that interfacial oxide is denser than the ‘‘bulk.’’ The data on deposited oxides suggest that caution must be exercised in extending the analysis to their case.
Optimization of molecular structures by self-consistent and nonlocal density-functional theory
Authors: Fan Liangyou , Ziegler Tom
Published: July 2002

An algorithm for the calculation of energy gradients has been implemented into the linear combination of atomic orbitals-Hartree–Fock–Slater (LCAO-HFS) program due to Baerends et al. [Chem. Phys. 2, 41 (1973)], and tested in connection with geometry optimizations of transition-metal complexes, organic molecules and compounds of main group elements. The algorithm is based on a self-consistent nonlocal density-functional method (NL-SCF) combining the nonlocal exchange correction by Becke [Phys. Rev. A 38, 3098 (1988)] with the nonlocal correlation correction by Perdew [Phys. Rev. B 33, 8822 (1986)]. It is shown that nonlocal corrections to the local-density approximation (LDA) improves the calculated metal-ligand bond distances considerably. Full optimizations of MnO−4, Cr(CO)6, Mo(CO)6, Fe(CO)5, Ni(CO)4, HMn(CO)5, HCo(CO)4, Fe(C5H5)2, and C5H5NiNO revealed that the LDA underestimates metal-ligand bond distances by an average of 0.05 Å, whereas nonlocal corrections, on the average, reduce the error to 0.01 Å. Nonlocal corrections are not as important for organic molecules and compounds of main group elements where LDA already affords bond distances in good agreement with experiment. Bond angles are, in general, not influenced much by nonlocal corrections. The nonlocal corrections increase the computational time involved by a factor of 4 on a scalar machine and a factor of 2 on a vector machine.
Some multivariable orthogonal polynomials of the Askey tableau-discrete families
Authors: Tratnik M. V.
Published: July 2002

A multivariable generalization is presented for all the discrete families of the Askey tableau. This significantly extends the multivariable Hahn polynomials introduced by Karlin and McGregor. The latter are recovered as a limit case from a family of multivariable Racah polynomials.
Surface magnetization of metals
Authors: Nedorezov S. S. , Rofe-Beketova E. F.
Published: July 2002

The surface magnetization of metals associated with electrons whose orbits are tangential to the metal boundary is investigated, taking into account anisotropy in the energy spectrum of conduction electrons. It is shown that the angular dependence of magnetization has peculiarities determined by the curvature of the Fermi surface at the reference points. Explicit expressions have been obtained for the surface magnetic susceptibility of electrons in bismuth, and appropriate numerical estimates of its value have been made.
New exact solutions of the Schrödinger equation with potentials of spin and soliton origin
Authors: Ulyanov V. V. , Zaslavskiı̆ O. B. , Vasilevskaya Yu. V.
Published: July 2002

New classes of exact solutions of the Schrödinger equation with simple explicit analytic expressions for potential fields, energy levels, and wave functions of stationary states are considered. The solutions are discovered with the help of new original methods elaborated in the quantum theory of spin systems. The corresponding effective potentials are compared to similar models of soliton origin. The main attention is paid to peculiar phenomena such as quasi-exact solvability, potentials with multiple and flexible profiles, fourth-order extrema, finite-band spectra and structural transformations in energy bands, and the spin–soliton analogy.
The role of long-wave longitudinal phonons in kinetics of insulators
Authors: Gurzhi R. N. , Yanovskiı̆ A. V.
Published: July 2002

It is shown that long-wave longitudinal phonons considerably affect heat transfer in most of existing crystals in spite of symmetry degeneracy of transverse vibrational branches. This is because of close values of phase velocity of transverse phonon modes in these crystals. Such effects are most pronounced in phonon hydrodynamics and in the propagation of second sound. It is shown that the thermal conductivity of bulk samples is a nonmonotonic function of the parameter characterizing the difference between the velocities of transverse modes.
Thermomechanical effects in thermal expansion of Ar–N2-type solid solutions
Authors: Aleksandrovskii A. N. , Chishko K. A. , Esel’son V. B. , Manzhelii V. G. , Udovidchenko B. G.
Published: July 2002

The results of analysis of hysteresis in the thermal expansion of solid solutions Ar–4.89 mol. %N2 are considered in the temperature range 1–16 K. A physical model is proposed in order to explain the observed phenomenon. This model is based on the assumption that transformed regions in the form of piles of random stacking faults in the initial fcc lattice are formed in the vicinity of nitrogen impurity. The hysteresis of the thermal expansion coefficient is due to relaxation mechanisms for thermal stresses appearing in the transformed region during thermocycling of the sample. The theoretical estimates of the upper and lower temperature boundaries of hysteresis phenomenon obtained in this model are in good agreement with the experimentally observed values.
Nonlinear resonant tunneling through doubly degenerate state of quantum well
Authors: Ermakov V. N. , Ponezha E. A.
Published: July 2002

Tunneling of electrons through a double-barrier system is considered in the approximation of low-transparency barriers taking into account the Coulomb interaction of electrons in the interbarrier space (quantum well). The state of the electrons in the quantum well is supposed to be doubly degenerate. It is shown that the dependence of the tunneling current on the applied voltage has a step-like form at low temperatures and has a threshold in the low-voltage region. The system under consideration also exhibits bistability.
Dynamic susceptibility of spin-1/2 Ising chain in transverse field
Authors: Derzhko O. , Krokhmalskii T.
Published: July 2002

Dynamic susceptibility of the one-dimensional spin-1/2 transverse Ising model is obtained by using the numerical approach suggested earlier [Ferroelectrics 153, 55 (1996)]. The dependence of the susceptibility frequency shapes on the value of the transverse field at various temperatures is discussed. The way in which the frequency shape rebuilds as the transverse field increases is illustrated.
Metallic point contacts formed by physical vapor deposition and chemical vapor deposition: microscopy study and point-contact spectroscopy
Authors: Gribov N. N. , Caro J. , Oosterlaken T. G. M. , Radelaar S.
Published: July 2002

We have made an electron-microscopy study of nanoholes in membranes in successive stages of metal deposition using two different techniques: physical vapor deposition (PVD) and chemical vapor deposition (CVD). One-sided PVD (thermal evaporation) of gold and silver was used, as is relevant for heterocontacts. The key results in this case are: 1) the holes are not filled during deposition and 2) closing of the holes is accomplished by lateral growth of the film on the membrane. In the case of CVD of tungsten we found that nanoholes in membranes are filled at the beginning of the deposition, and that the process is capable of filling holes as small as 10 nm. Fabricated devices (α-tungsten) show good quality point-contact spectra which are characteristic of ballistic transport through the constriction. A very interesting stepwise current increase was observed for one amorphous tungsten point contact.
Dilatometric size effect in thin C60 films
Authors: Pugachev A. T. , Churakova N. P. , Gorbenko N. I.
Published: July 2002

The change in the lattice parameter Δa/a of monocrystalline C60 films of thickness less than 10 nm is determined by the transmission high-energy electron diffraction method. In the temperature range 90–260 K, the value of Δa/a increases with decreasing film thickness. The results are used for calculating the coefficients αf and αs of linear thermal expansion of the films and of the surface atomic layer. The value of αs along the (111) plane is equal to (55±15)×10−6 K−1.
Study of surface phenomena in the ferroelastic phase transition in a semi-infinite crystal
Authors: Lavrinenko N. M.
Published: July 2002

Surface phenomena are studied during ferroelastic phase transition in a semi-infinite crystal with tetragonal symmetry. It is shown that the strictional bond between the order parameter and lattice deformation leads to the emergence of a spatially modulated structure with a finite value of the wave vector at the surface phase transition point. The surface phase transition always precedes the ferroelastic phase transition in the bulk.
Relaxation of concentration and temperature in superfluid mixtures He3–4He at low temperatures
Authors: Nemchenko K. È.
Published: July 2002

It is shown on the basis of the solution of the kinetic equation for the gas of impurity excitations of superfluid mixtures He3–4He that the relaxation of concentration and temperature occurs due to two modes (acoustic and dissipative). The parameters characterizing these modes are determined. The obtained results show that the relaxation of concentration and temperature of impuritons is completely determined by the thermal conductivity of the mixture and by the acoustic mode (second sound).
Hydrodynamic asymptote of Green’s functions of a weakly anisotropic multisublattice magnet
Authors: Isayev A. A.
Published: July 2002

The hydrodynamic asymptote of Green’s functions is determined for weakly anisotropic multisublattice magnets whose reduced description parameters are the total spin density and the matrix of rotation in the spin space. Spectra of spin waves are obtained and the number of Goldstone and activation modes is determined.
Photon excitation of the third molecular continuum in solid krypton
Authors: Ogurtsov A. N. , Savchenko E. V. , Becker J. , Runne M. , Zimmerer G.
Published: July 2002

Luminescence study of the near-ultraviolet continuum in nominally pure solid krypton under selective excitation by synchrotron radiation is presented. Intrinsic nature of the emission has been established. Clear threshold behavior at the band gap energy reveals the key role of the electron-hole pairs in a population of the continuum forming states.
New channels of photon echo relaxation in Y2SiO5:Pr3+ and LaF3:Pr3+ crystals
Authors: Malyukin Yu. V.
Published: July 2002

Experimental results on the investigation of low-temperature optical absorption spectra and temperature dependence of the photon echo (PE) amplitude signal in Y2SiO5:Pr3+ and LaF3:Pr3+ crystals at the transition H43(0)−3P0 of the Pr3+ ion are presented. It is shown that additional relaxation channels exist for PE in addition to the known phonon mechanisms. This is associated in a LaF3:Pr3+ crystal with the temperature variation of dipole moment at the Pr3+ ion transition. In a Y2SiO5:Pr3+ crystal, this is due to the thermally activated transitions for the Pr3+ ion between nonequivalent positions in the crystal lattice.
Reflection and transformation of acoustic waves at the interface in superfluid He3-A
Authors: Kekutiya Sh. E. , Chkhaidze N. D.
Published: July 2002

The reflection and transformation of acoustic waves in He3-A and He3-A1 is considered in two cases: (1) at the boundary of a solid impermeable wall for an arbitrary angle of incidence, and (2) for a normal incidence of waves at the interface between a free liquid and a system of periodic plane-parallel capillaries filling the half-space. In the first case, the reflection coefficient of first and second sounds, spin and spin–temperature waves, and the coefficients of mutual transformation of these waves are calculated. It is shown that a longitudinal spin wave is not transformed into other waves and experiences instead the total reflection at the solid wall. The angle of incidence for which the energy attenuation coefficient of first sound attains its maximum value is calculated as well as the angular interval corresponding to attenuation and total internal reflection of second sound. In the second case, the coefficients of excitation of fourth sound and of a magnetoacoustic wave by the first and second sounds, the reflection coefficients for the first and second sounds and for a longitudinal spin wave, the coefficient of transformation of first sound into second sound and vice versa, and the coefficient of reflection of fourth sound at the interface between the capillary system and the free liquid, and the coefficient of excitation of a longitudinal spin wave in free helium by the same wave in a capillary are calculated.
Finite temperature effects in the Fermi liquid theory of the diffusion of He4 in He3
Authors: Hjort H. H. , Culman T. G. , Edwards D. O. , He Jizhong
Published: July 2002

The diffusion coefficient D and the thermal diffusion ratio kT for dilute He4 in liquidHe3 are calculated from Fermi liquid theory. The collision integral assumes a scattering amplitude a34 expanded in scalar combinations of the quasiparticle momenta. As T→0, D varies as 1/T and kT/c, where c is the concentration, approaches a constant. As shown previously, the limits for DT and kT/c are determined by thermodynamic properties, the He4 effective mass and partial volume, and properties of pure He3. We have decreased kT/c by a few percent, by including the effect of ∇T on the He3 distribution function. The temperature dependence of DT and kT/c is linear and related to the coefficients in the expansion of a34. Two coefficients can be found from thermodynamics. A conjecture about the remainder suggests that DT may have a maximum between 0 and 0.5 K.
Faraday rotation in conductors with magnetoimpurity electron states
Authors: Ermolaev A. M. , Rashba G. I.
Published: July 2002

The high-frequency Hall conductivity for metals and degenerate semiconductors with magnetoimpurity electron states is calculated. The effect of these states both on Faraday rotation angle and on magnetic circular dichroism is considered. Additional maxima and minima on the frequency dependence of Faraday angle, which are associated with the magnetoimpurity electron states, are observed.
Oscillations of the spectrum of acoustic phonons interacting with composite fermions
Authors: Zazunov A. L. , Fil D. V.
Published: July 2002

The interaction of collective excitations in a composite fermion system with phonon modes is considered. It is shown that for parameters corresponding to real systems in which the fractional quantum Hall effect is observed, the phase velocity of acoustic phonons has an oscillating dependence on the wave vector. The obtained oscillating structure of the phonon spectrum is determined to a considerable extent by the external magnetic field and electron concentration.
Mechanisms for increasing resolution of high-frequency PC spectroscopy
Authors: Balkashin O. P.
Published: July 2002

It is shown that the improvement of resolution of high-frequency PC spectroscopy is due to a decrease in the contribution of thermal effects and nonequilibrium phonon reabsorption to the signal being measured.
Classical mesoscopic effect in the resistance of point contacts
Authors: Kolesnichenko Yu. A. , Omelyanchouk A. N. , van der Post N. , Yanson A. I.
Published: July 2002

The mesoscopic effect of the dependence of the point-contact conductance on the spatial distribution of the impurities is theoretically studied. It is shown that the resistance dependence on the diameter d is not only determined by the electron mean free path li, but also by the average distance between the impurities. In the case of two types of impurities with different concentrations the mesoscopic effect is predicted for a dirty point contact (d≫li) due to the scattering at specific (e.g., magnetic) impurities with a low concentration. Such contacts were numerically modeled for random distributions of the two types of impurities.
Propagation of fourth sound in a solution of two superfluid liquids taking the drag effect into account
Authors: Vilchinsky S. I.
Published: July 2002

The propagation of fourth sound waves in a solution of two superfluid liquids He3-He4 is considered by taking into account the effect of reciprocal drag of superfluid motions. It is shown that the inclusion of the drag effect leads to a change in the ratio of intensities of second and first fourth sound waves.
Correlation of the properties of high-Tc superconductor La2−xSrxCuO4 and anharmonicity of atomic potentials
Authors: Chudinov V. G. , Chirkov A. G. , Nurgayanov R. R.
Published: July 2002

The molecular dynamics method is applied to the La2−xSrxCuO4 system to prove that canonicity conditions are violated in the case of a large contribution of anharmonism. This can lead to the formation of “hot” regions ∼0.5 nm in the vicinity of Sr impurity atoms with an average kinetic energy two or three orders of magnitude higher than in the matrix even at low temperatures. The matrix is “effectively” cooled and can basically carry superconducting current due to percolation for any electron pairing mechanism. The velocity distribution is described by not one but at least two Maxwell functions. The fcc lattice of Ni near the phase-transition point also acquires “hot” spots which are not, however, localized in space, but migrate (with a lifetime ∼10−12 s) and have a much smaller difference in kinetic energies (by a factor of 1.5–2.0). At low temperatures, canonicity conditions are always satisfied.
Point-contact spectroscopy of organic conductors [(C2H5)4N]0.5[Ni(dmit)2] and (BEDT-TTF)2I3
Authors: Kamarchuk G. V. , Khotkevich A. V. , Bagatskii V. M. , Kravchenko A. V.
Published: July 2002

Point-contact spectra of organic conductors [(C2H5)4N]0.5[Ni(dmit)2] and (BEDT-TTF)2I3 have been measured. The plots of point-contact functions of the electron–phonon interaction in these compounds have been constructed, and mean and root-mean-square values of frequency have been obtained. The relation between the intensity of the electron-vibrational interaction and conducting properties of the materials under investigation have been obtained. A correlation is observed between the intensity of these processes and the superconducting transition temperature. The criterion for the synthesis of new organic superconductors is discussed.
Lambda point thermodynamics of confined liquid helium: negative surface specific heat
Authors: Ferrell R. A. , Bhattacharjee J. K.
Published: July 2002

We present some theoretical considerations that are relevant to the forthcoming measurements in microgravity of the specific heat of confined liquid helium (the flight experiment “CHEX”). Primary attention is devoted to the suppression near the boundaries, the “negative surface specific heat.” Above the lambda point, we compute this to lowest order in the ε-expansion: below the lambda point our discussion is more restricted.
Reconstruction of the charged surface of liquid hydrogen
Authors: Kolmakov G. V. , Levchenko A. A. , Mezhov-Deglin L. P. , Trusov A. B.
Published: July 2002

The evolution of shape of the surface of equipotentially charged liquid hydrogen film condensed on the lower or upper plate of a horizontally placed diode in external electric fields has been studied experimentally under the condition of total compensation of the applied field by the surface charge. Reconstruction phenomenon—the formation of a solitary wave (soliton)—has been observed in an electric field higher than some critical value for the film that covers the lower plate.
Analysis of the shift in the superconducting transition under pressure in the Anderson–Hubbard two-orbital model
Authors: Kosov A. A.
Published: July 2002

The two-orbital Hubbard model is used to obtain formulas for the fermion excitation spectrum in the energy bands hybridized by Anderson’s interaction. A transition to the Hubbard operators, which diagonalizes the one-site part of the Hamiltonian, allows us to use the Green’s temperature function technique to take into account the interstitial jump term while studying the superconducting properties of the model. An analysis of the lower part of the energy spectrum leads to a formula for the superconducting transition temperature Tc associated with the pairing of quasiparticles in one of the correlated bands. The dependence of Tc on electron concentration and energy parameters determining the intraatomic correlation is studied. Proposing a simple relation between the value of pressure (P) and width of the correlated band, the dependence of Tc on the pressure was defined. Good agreement between the theoretical calculation of the dependence of Tc on the pressure and the experimental results for Y1−xPrxBa2Cu3O7−δ is found. Comparison of the theoretical and experimental results for the dependence of Tc and its derivative d(ln Tc)/dP on Sr and Bi-content (x) in La2−xSrxCuO4 has been made. It is concluded that the model under consideration can be used for the description of the shift in Tc under pressure for a number of superconductors.
Electron sound in aluminum. Electron–electron scattering
Authors: Bezuglyi E. V. , Burma N. G. , Gaiduk A. L. , Kolobov I. G. , Fil’ V. D. , Khotkevich V. V. , van Kempen H.
Published: July 2002

The relaxation parameters of charge carriers in aluminum are measured by investigating the attenuation of electron sound and acoustic wave transfer under Doppler-shifted cyclotron resonance. It is shown that the electron–electron relaxation rate at spherical parts of the hole sheet of the Fermi surface is close to the results of the theory (A. Jaquier et al., Phys. Rev. B52, 13005 (1995)) that takes into account the electron–electron interaction with the exchange of virtual phonons. At the same time, the experimental anisotropy of the electron–electron scattering is considerably smaller than the calculated value. A noticeable anisotropy of the electron–impurity collisions frequency in aluminum is discovered.
Resistive state of HTSC film in a varying magnetic field
Authors: Palti A. M. , Ruban A. I. , Snarskii A. A.
Published: July 2002

The frequency dependence of dissipation in a varying external magnetic field perpendicular to a HTSC film is calculated by using the percolation model. The dependence is linear at low frequencies and has a peak at high frequencies. The linear frequency dependence of dissipation in the low-frequency region is confirmed by the results of experimental studies of current–voltage characteristics.
Low-temperature properties of two XY spin chains with a point contact
Authors: Ezerskaya E. V.
Published: July 2002

The energy spectrum of a one-dimensional, exactly solvable spin model formed by two semi-infinite XY spin chains with spin s=1/2 with a point-contact interaction in a longitudinal magnetic field is calculated. It is shown that the spectrum of such a system can contain one or two local energy levels apart from two bands overlapping in weak fields. Local thermodynamic parameters of the chains can have singularities at zero temperature.
Dependence of the superconducting transition temperature on the thickness of superconducting films with different coherence lengths
Authors: Prokhorov V. G.
Published: July 2002

The dependence of the superconducting transition temperature on the thickness of films of niobium, VN, TaN, and YBa2Cu3O7−x are determined experimentally. It is shown that, in addition to the proximity effect, the fluctuations of the electromagnetic field and order parameter of the superconducting phase may also play a significant role in superconductors with a small coherence length.
Size-effect of Kondo scattering in point contacts (revisited)
Authors: Yanson I. K. , Fisun V. V. , Bobrov N. L. , Mydosh J. A. , van Ruitenbeek J. M.
Published: July 2002

The size-effect of Kondo-scattering in nanometer-sized metallic point contacts is measured with the simplified, mechanically-controlled break–junction technique for CuMn alloy of different Mn concentrations: 0.017; 0.035; and 0.18 (±0.017) at.%. The results are compared with our previous publication on nominally 0.1 at. % CuMn alloy.Reference 1Reference 2 The increase of width of the Kondo resonance and enhanced ratio of Kondo-peak intensity to electron–phonon scattering intensity is observed for contacts with sizes smaller than 10 nm. From the comparison of electron–phonon scattering intensity for the pressure-type contacts, which correspond to the clean orifice model, we conclude that the size effect is observed in clean contacts with the shape of a channel (nanowire).
Effects of nonlocal interlayer exchange in spin dynamics of a magnetic metal superlattice
Authors: Tarasenko S. V.
Published: July 2002

It is shown that a consistent analysis of the nonlocal interlayer exchange in semi-confined metallic magnetic superlattice of the ferromagnet–nonmagnetic metal type with antiferromagnetic coupling between ferromagnetic layers leads to the formation of new types of collective dipole–exchange spin-wave excitations near the surface of the magnetic superlattice.
Magnetic transport properties of semimagnetic semiconductor Hg1−x−yCrxMnySe
Authors: Prozorovskiı̆ V. D. , Reshidova I. Yu. , Puzynya A. I. , Paranchich S. Yu.
Published: July 2002

Experimental results of investigations of monocrystalline samples of Hg1−x−yCrxMnySe solid solution indicate, first, a considerable influence of manganese atoms introduced in Hg1−xCrxSe on the absolute values of physical parameters such as magnetic susceptibility, phase-transition temperature, mobility of conduction electrons, and the period of time during which the samples go over to the equilibrium state, and second, the formation of materials with improved electrophysical and clearly pronounced magnetic characteristics as compared with Hg1−xCrxSe samples with the same concentration of chromium ions.
Generalization of equal-module exchange magnetic classes
Authors: Borlakov Kh. Sh.
Published: July 2002

It is shown that in addition to equal-module exchange structures satisfying the criterion for the existence of the Andreev–Marchenko and Bar’yakhtar–Yablonskii spin scalar, other equal-module exchange structures also exist. In contrast to the structures obtained from the condition for the existence of a spin scalar, the latter follow from thermodynamic conditions and correspond to thermodynamically stable phases. Besides, these structures are not related to the restrictions imposed on the dimensionality of irreducible representation typical of the structures of the former kind.
Kinetics of diffusion mode in a phonon–impuriton system of He3–4He mixtures of quantum liquids
Authors: Nemchenko K. È.
Published: July 2002

Relaxation processes in a phonon–impuriton systems of superfluid He3–4He mixtures are studied on the basis of the system of kinetic equations. The obtained general energy–momentum relations are valid for any ratio of the times of phonon–impuriton interaction to the times of equilibrium stabilization in the phonon and impuriton subsystems. In the hydrodynamic and kinetic modes of phonon rates, the effective diffusion coefficient for the dissipative mode as well as the velocity and attenuation of sound in the acoustic mode are calculated.
Amorphous–crystalline films of fullerite C60
Authors: Gorbenko N. I. , Zubarev E. N. , Medvedev S. A. , Pugachev A. T. , Churakova N. P.
Published: July 2002

Fullerite C60 films obtained by evaporation and condensation of C60 molecules on a cooled glass surface are investigated by high-resolution electron-optical methods (including direct lattice resolution and selected area diffraction). It is found that the films have an amorphous–crystalline structure, the amount of amorphous phase reaching 70%. Diffraction patterns of amorphous fullerite are obtained. The values of 4π(sin θ)/λ are determined for the first three halos. The positions of halos indicate that the structure of amorphous fullerite can be described by the hard spheres liquid model.
On correlation effects in a narrow-band model with electron–hole asymmetry
Authors: Didukh L. D. , Hankevych V. V.
Published: July 2002

Some correlation effects are studied in a narrow-band model with electron–hole asymmetry. A peculiar feature of the model is that it takes into account the hopping integral associated with electron–electron interaction (correlated hopping). The method of Green’s functions is used to find the quasiparticle energy spectrum, as well as expressions for the upper and lower Hubbard subband widths. It is shown that the specific features of the model lead in a number of cases to consequences differing significantly from those following from the Hubbard model. The obtained results mainly illustrate the peculiarities of the model in the low-temperature region and are used for interpreting the physical properties of systems with narrow energy bands.
On a possible reason behind the anisotropy observed in the superconducting properties of underdoped cuprates
Authors: Loktev V. M. , Quick R. M. , Sharapov S. G.
Published: July 2002

An attempt is made to interpret the experiments in which the superconducting transition temperature in underdoped HTSC was found to depend on the direction of the current passing through the sample. It is suggested that one (higher) temperature approximately corresponds to the point TBKT of the two-dimensional transition, while the other is the temperature Tc corresponding to 3D ordering between layers. For conditions when Tc⩾TBKT (relatively high values of carrier concentration and interlayer coupling), the anisotropy of the superconducting properties becomes negligible and the layered system possesses only one critical temperature.
On the ground state of the Hubbard model with strong repulsion
Authors: Mikhailova Ju. V.
Published: July 2002

The exact result is obtained for a square (cubic) Hubbard lattice with an infinitely large repulsion energy U: the ferromagnetic state with the maximum spin is not the ground state of the system if the number of holes is equal to two.