Reduction in the rate of phonon scattering by a spatially correlated system of iron ions and low-temperature “anomaly” of the thermoelectric phenomena in HgSe:Fe crystals

A new effect of the reduction in the rate of phonon scattering by the spatially correlated system of iron ions in HgSe:Fe crystals is detected experimentally and calculated theoretically. The thermoelectric power is measured using HgSe:Fe samples with different iron content in the temperature range 7.5–60 K. It is found that the dependence of the thermoelectric power on iron content exhibits remarkable features at T<10 K: the quantity |α(N _Fe )| increases as the iron concentration increases to N _Fe =5×10¹⁸ cm⁻³, reaches a maximum at N _Fe ≈(1–2)×10¹⁹ cm⁻³, but then monotonically decreases with further increases in N _Fe . It is shown that the obseved increase in the thermoelectric power is due to a reduction in the rate of phonon scattering by the spatially correlated system of Fe³⁺ ions. This new effect is analyzed theoretically, and the theoretical results are compared with the experimental data. Zh. éksp. Teor. Fiz. 114, 191–207 (July 1998)     

Carrier mobility in nonstoichiometric n-Bi2Te3−x Sex solid solutions

A study has been made of the thermoelectric and galvanomagnetic properties of n-Bi₂Te_3−x Se_x solid solutions (x=0.3 and 0.36) in the temperature range 80–300 K. The lowest carrier concentrations, (0.8–1)×10¹⁸ cm⁻³, were obtained by displacing the solid solution from the stoichiometric to a Te-rich composition. At such carrier concentrations, the second subband in the conduction band of n-Bi₂Te_3−x Se_x is not filled, which results in a growth of mobility because of the absence of interband scattering, and brings about an increase of thermoelectric efficiency in the 80–120-K range. Fiz. Tverd. Tela (St. Petersburg) 39, 483–487 (March 1997)     

Schwarzschild black hole with global monopole charge

We derive the metric for a Schwarzschild black hole with global monopole charge by relaxing asymptotic flatness of the Schwarzschild field. We then study the effect of global monopole charge on particle orbits and the Hawking radiation. It turns out that existence, boundedness and stability of circular orbits scale up by (1−8πη ²)⁻¹, and the perihelion shift and the light bending by (1−8πη ²)^−3/2, while the Hawking temperature scales down by (1−8πη ²)² the Schwarzschild values. Hereη is the global charge.     

The decay φ→η″γ

A search for the process e ⁺ e ⁻→φ(1020)→η″(958) γ in the decay channel η″→π ⁺ π ⁻ η, η→γγ was made in an experiment at the VEPP-2M e ⁺ e ⁻ collider with the SND detector. Analysis confirms the occurrence of φ→η″γ decay with probability B(φ→η″ γ)=(6.7 _−2.9 ^+3.4 )×10⁻⁵. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 2, 87–91 (25 January 1999)     

Mechanism for the influence of the geometric parameters on the electrical characteristics of Penning ion sources

A steady-state Penning ion source is studied experimentally. Depending on the geometric parameter l _a (the anode length to diameter ratio) and pressure, maxima are observed in the discharge current and in the ion beam current extracted from an aperture at the center of the cathode. It is shown that at pressures of the order of 10⁻⁴ Torr, two maxima appear in these currents: one, for short discharge gaps with l _a =1–1.5, corresponds to a diverging ion beam, and the other, for longer anodes with l _a =4–5, to a collimated ion beam. At pressures of the order of 10⁻⁵ Torr, only one maximum appears in these currents, for short anodes l _a =2–3 with a diverging ion beam. A physical explanation is proposed for these findings. Zh. Tekh. Fiz. 68, 29–32 (September 1998)     

Internal waves in a compressible two-layer model atmosphere: Hamiltonian description

We consider slow, compared to the speed of sound, motions of an ideal compressible fluid (gas) in a gravitational field in the presence of two isentropic layers with a small specific-entropy difference between them. Assuming the flow to be potential in each of the layers (v _{1, 2} = ▿ϕ_{1, 2}) and neglecting the acoustic degrees of freedom (div($ \bar \rho $ \bar \rho (z)▿ϕ_{1, 2}) ≈ 0, where $ \bar \rho $ \bar \rho (z) is the average equilibrium density), we derive the equations of motion for the boundary in terms of the shape of the surface z = η(x, y, t) itself and the difference between the boundary values of the two velocity field potentials: ψ(x, y, t) = ψ₁ − ψ₂. We prove the Hamilto nian structure of the derived equations specified by a Lagrangian of the form ℒ = ∫$ \bar \rho $ \bar \rho (η)η _t ψdxdy − ℋ{η, ψ}. The system under consideration is the simplest theoretical model for studying internal waves in a sharply stratified atmosphere in which the decrease in equilibrium gas density due to gas compressibility with increasing height is essentially taken into account. For plane flows, we make a generalization to the case where each of the layers has its own constant potential vorticity. We investigate a system with a model dependence $ \bar \rho $ \bar \rho (z) ∝ e ^−2αz with which the Hamiltonian ℋ{η, ψ} can be represented explicitly. We consider a long-wavelength dynamic regime with dispersion corrections and derive an approximate nonlinear equation of the form u _t + auu _x − b[−$ \hat \partial _x^2 $ \hat \partial _x^2 + α²]^1/2 u _x = 0 (Smith’s equation) for the slow evolution of a traveling wave.     

How the recent BABAR data for P → γγ* affect the Standard Model predictions for the rare decays P → l+l?

Measuring the lepton anomalous magnetic moments (g − 2) and the rare decays of light pseudoscalar mesons into lepton pairs P → l ⁺ l ⁻, serve as important tests of the Standard Model. To reduce the theoretical uncertainty in the standard model predictions, the data on the charge and transition form factors of the light pseudoscalar mesons play a significant role. Recently, new data on the behavior of the transition form factors P → γγ* at large momentum transfer were supplied by the BABAR collaboration. There are several problems with the theoretical interpretation of these data: (1) An unexpectedly slow decrease of the pion transition form factor at high momenta, (2) the qualitative difference in the behavior of the pion form factor and the η and η′ form factors at high momenta, (3) the inconsistency of the measured ratio of the η and η′ form factors with the predicted one. We comment on the influence of the new BABAR data on the rare decay branchings.     

Di-pion emission in heavy quarkonia decays

The dipion spectrum for the ϒ(nS) → ϒ(n′S) transition with n < 4 has the form dw/dq ∼ (phase space) |η − x|², with x = q ² − 4m _π² / (ΔM)² − 4m _π² < q ² ≡ M _ππ², and ΔM = M(nS) − M(n′S). The parameter η is calculated and the spectrum is shown to reproduce the experimental data for all three types of decays: 3 → 1, 2 → 1, and 3 → 2 with η ≈ 0.5, 0, and −3, respectively. The text was submitted by the author in English.     

Magnetically induced spatial dispersion in the cubic magnetic semiconductors Cd1−x MnxTe

In the transverse geometry we have detected birefringence that is linear in the magnetic field B and the light wave vector k in the cubic magnetic semiconductors Cd_1−x Mn_xTe (0⩽x⩽0.52). The effect was found to be large, ∼1 (deg cm⁻¹ T⁻¹), and highly anisotropic, in contrast to the Faraday and Voigt effects. The phenomenon is represented by terms of type γ _ijklB_kk_l in the permittivity tensor ε _ij and can be described by two parameters, A and g. Spectral studies have shown that the normalized parameters A/x and g/x are independent of x, i.e., the effect can be related to the Mn²⁺ ions. Below the edge E _g of the forbidden band, the dispersion of A is described by a (E _g−E)^−1.4-dependence, while the dispersion of g is nil. Theoretical analysis has shown that the spectral curves for A and g can be explained by the special features of the dispersion laws for electrons and holes (features related to the fact that there is no inversion center) and by the dependence of the parameters of the exchange interaction on the electron wave vector. Zh. éksp. Teor. Fiz. 114, 1018–1033 (September 1998)     

One Dimensional Behavior of Singular N Dimensional Solutions of Semilinear Heat Equations

We consider u(x,t) a solution of u _t =Δu+|u| ^{p − 1} u that blows up at time T, where u:ℝ ^N ×[0, T)→ℝ, p>1, (N−2)p<N+2 and either u(0)≥ 0 or (3N−4)p<3N+8. We are concerned with the behavior of the solution near a non isolated blow-up point, as T−t→ 0. Under a non-degeneracy condition and assuming that the blow-up set is locally continuous and N−1 dimensional, we escape logarithmic scales of the variable T−t and give a sharper expansion of the solution with the much smaller error term (T−t)^{1, 1/2−η} for any η>0. In particular, if in addition p>3, then the solution is very close to a superposition of one dimensional solutions as functions of the distance to the blow-up set. Finally, we prove that the mere hypothesis that the blow-up set is continuous implies that it is C ^{1, 1/2−η} for any η>0. Received: 20 June 2001 / Accepted: 6 October 2001     

Electrical transport properties of CuWO4

The temperature dependence of the electrical conductivity, thermoelectric power and dielectric constant of the antiferromagnetic CuWO₄ have been studied in the temperature range 300–1000 K. The conductivity results can be summarised by the equations σ_I=6.31 × 10⁻³ exp (−0.29 eV/kT) ohm⁻¹ cm⁻¹ in the temperature range 300–600 K and σ_II=3.16 × 10⁵ exp (−1.48 eV/kT) ohm⁻¹ cm⁻¹ between 600 K and 1000 K. The thermoelectric power can be expressed byθ=[− 1.25 (10³/T) + 3.9] mV/K. Initially dielectric constant increases slowly but for high temperatures its increase is fast.     

Coercivity of homogenized ensembles of anisotropic γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

The influence of interaction between anisotropic γ-Fe₂O₃ nanoparticles on their coercive force H _c is studied. In samples where the degree of homogenization of anisotropic γ-Fe₂O₃ nanoparticles is high owing to mechanical, ultrasonic, and magnetic dispersion with subsequent filtering of resulting suspensions, H _c is almost independent of volume concentration η of the particles when η varies between 4 × 10⁻⁴ and 10⁻¹. In samples homogenized only mechanically, the H _c versus logη dependence is linear.     

On mass corrections to the decay <Emphasis Type="Italic">P</Emphasis> → <Emphasis Type="Italic">l</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">l</Emphasis><Superscript>−</Superscript>

The Mellin-Barnes representation is used to improve the theoretical estimate of mass corrections to the width of a light pseudoscalar meson decay into a lepton pair, P → l ⁺ l ⁻. The full resummation of the terms ln(m _l ²/Λ²)(m _l ²/Λ²) ⁿ and (m _l ²/Λ²) ⁿ to the decay amplitude is performed, where m _l is the lepton mass and Λ ≈ m _ρ is the characteristic scale of the P → γ*γ* form factor. The total effect of the mass corrections for the e ⁺ e ⁻ channel is negligible and, for the μ⁺μ⁻channel, its order is of a few percent. The text was submitted by the authors in English.     

Determination of hadronic partial widths for scalar-isoscalar resonances f0(980), f0(1300), f0(1500), f0(1750) and the broad state f0(1530 ?250+90 )

Recently [see V.V. Anisovich et al., Yad. Fiz. 63, 1489 (2000)], the K-matrix solutions for the wave IJ ^PC=00⁺⁺ were obtained in the mass region 450–1900 MeV, where four resonances f ₀(980), f ₀(1300), f ₀(1500), f ₀(1750) and the broad state f ₀(1530 ₋₂₅₀ ⁺⁹⁰ ) are located. Based on these solutions, partial widths are determined for scalar-isoscalar states decaying into the channels ππ, KK ηη, ηη′, ππππ and corresponding decay couplings. From Yadernaya Fizika, Vol. 65, No. 8, 2002, pp. 1583–1590. Original English Text Copyright ? 2002 by Anisovich, Nikonov, Sarantsev. This article was submitted by the authors in English.     

Magnetoplastic effect in LiF crystals and longitudinal spin relaxation

New features of the dependence of the average travel distance l of dislocations on the magnetic field B have been found in an investigation of the magnetostimulated dislocation mobility in LiF crystals: A transition has been found from ordinary proportionality l∝B ² to saturation l≈ const in high fields B. It is shown that the experimental points can be described satisfactorily by the theoretical dependence l∝ [(B ₀/B)²+1]⁻¹ (B ₀≈0.8 T), typical for the mechanism of longitudinal spin relaxation in a system of radical pairs, which are supposedly formed when dislocation nuclei interact with paramagnetic impurity centers. According to the theory, the level of the field B ₀ is determined by the characteristic frequency of the oscillations of the internal fields in the lattice, which for B ₀∼1 T is of the order of 10¹¹s⁻¹, which corresponds to the typical frequency of characteristic oscillations of dislocation segments between pinning centers, which, naturally, does not depend on temperature. This in turn explains the fact that the measured values of B ₀ are the same at 293 K and 77 K. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 11, 749–753 (10 December 1999)     

Analysis of the decays ψ′ → J/ψπ+π? and η′c → ηcπ+π? with the heavy-quark symmetry

In this article, we study the decays ψ′ → J/ψπ ⁺ π ⁻ and η′_c → η _c π ⁺ π ⁻ by taking into account the chiral symmetry breaking effects, the final-state interactions and the heavy-quark symmetry. We can confront the predictions of the η′_c → η _c π ⁺ π ⁻ decay width and differential decay width with the experimental data in the future, and obtain powerful constraints on the chiral breaking effects and the final-state interactions, and test the heavy-quark symmetry.     

The effect of neutron and gamma irradiation on the dislocation relaxation peak in silver

Summary The internal-friction spectrum has been determined in extremely pure polycrystalline silver crystals after being subjected to neutron and gamma irradiation. The spectra obtained for an applied frequency of 10 MHz show that the mechanical losses due to dislocation relaxation decrease as the doses of neutron and gamma radiation increase. The effect of gamma radiation was found to be more significant than that of neutron irradiation. The relationship between damping neutron and gamma dose was found to be of the formQ _max ⁻¹ α ΛD ^η, where η is equal to −1.2 for neutron and −1.45 for gamma irradiation. The variations of the peak height and width, and temperature of the dislocation relaxation peak as functions of neutron and gamma doses are explained in terms of the pair-kink formation model.     

On the high-statistics investigation of the <Emphasis Type="Italic">a</Emphasis><Subscript>0</Subscript>(980) resonance in the γγ → π<Superscript>0</Superscript>η reaction

High-statistics data on the γγ → π⁰η reaction will make it possible to conclude whether the K ⁺ K ⁻-loop rescattering mechanism, γγ → K ⁺ K ⁻ → a ₀(980) → π⁰η, is the main mechanism of the production of a ₀(980) isovector resonance. This mechanism provides a reasonable value of 20–30 nb at the maximum for the manifestation of a ₀(980) in the γγ → π⁰η cross section. It also gives rise to a noticeable narrowing of the a ₀(980) peak to its effective (observed) width ≈20–30 MeV in the γγ → π⁰η channel. The decay width averaged over the resonance mass distribution is 〈Γ_{α 0} → K ⁺ K ⁻ → γγ〉_πη ≈ 0.13 keV. The experimental confirmation of this scenario would be important evidence in favor of the q ² $ \bar q $ \bar q ² nature of light scalar mesons.     

Effect of magnetic field on the sound velocity of a dilute Kramers-ion glass at low temperature

Recent results on the effect of magnetic field on the sound velocity V in aluminosilicate glasses doped with dysprosium are analyzed on the basis of a minimal model for the ground state of Dy³⁺ (Kramers ion with J=15/2) described by a wave function ϕ _± = ϕ _± J _m + ηϕ _{± 1/2}. The first term represents a state with a large J projection on the local crystal field axis and the random parameter η(〈η〉=0, 〈η ²〉≪1) introduces a small admixture of the state ϕ _±1/2 into the ground state. The relative variation of V due to the resonance interaction of sound waves with this state split by H is determined as a function of H and T. It possesses a universal asymptotic behavior. Our results are in reasonable agreement with the experiment. A possible structure of the crystal fields that can induce this state is discussed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 4, 341–346 (25 February 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Effect of constant-energy surface anisotropy on the thermoelectric figure-of-merit of the n-Bi2 (Te,Se,S)3 solid solutions

A study is reported of the thermoelectric and galvanomagnetic properties of n-Bi₂Te_3−x−y Se_xSe_y solid solutions for 0.12⩽x⩽0.36 and 0.12⩽y⩽0.21 within the 80–300 K temperature region. The thermoelectric figure-of-merit Z has been found to correlate with the parameters of the many-valley energy-band model including anisotropic carrier scattering. It is shown that a decrease in the constant-energy surface anisotropy and scattering anisotropy results in a growth of Z for optimum carrier concentrations in the solid solution. Fiz. Tverd. Tela (St. Petersburg) 41, 187–192 (February 1999)