de Haas-van Alphen oscillations and angular magnetoresistance oscillations in the organic metal κ-(BETS)2GaCl4

Quantum de Haas-van Alphen oscillations and semiclassical angular magnetoresistance oscillations are observed in the quasi-two-dimensional organic metal κ-(BETS)₂GaCl₄. The behavior of these oscillations attests to the existence of two cylindrical Fermi surface sheets with axes perpendicular to the conducting plane. The cross-sectional areas of these cylinders in the conducting plane are equal to about 20 and 100% of the corresponding cross section of the Brillouin zone. It is shown that the many-particle interaction can be suppressed significantly in this compound. Zh. éksp. Teor. Fiz. 115, 205–210 (January 1999)     

Oscillations of the magnetoresistance in an inclined magnetic field for MIS structures on (100) silicon with a high electron density

At electron densities N _S>6×10⁻² cm⁻²² a second series of oscillations, which are tentatively attributed to population of the second energy subband, is observed in addition to the main series of Shubnikov-de Haas oscillations. A change in phase of the oscillations of the second series is observed at some angle of inclination α_e of the field. The measured value of α_e is used to calculate the ratio of the cyclotron mass to the effective g factor. The maximum possible cyclotron mass is also determined as m _H< 0.32m _e. On this basis it is concluded that the second series of oscillations is due to electrons which have an in-plane effective mass m*≈0.2m _e and which belong to the same valleys of the Fermi surface as in the case of the main oscillations. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 136–140 (25 January 1998)     

Investigation of the reaction D(e, pp)e′ π − on a tensorpolarized deuterium target at high proton momenta

The differential cross section of the reaction D(e,pp)e′ π ⁻ is measured in the range of proton momenta 300–720 MeV/c and proton emergence angles 64–83° for invariant masses of the pp system ranging from 2m _p to 2220 MeV/c ². The measured values of the cross section are found to differ substantially from single-particle model calculations. The components of the analyzing power for this reaction are measured. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 730–736 (25 May 1998) Deceased.     

Cyclotron resonance in the organic conductor (BEDO-TTF)2ReO4(H2O) in the millimeter wavelength band

Resonant microwave absorption in a (BEDO-TTF)₂ReO₄(H₂O) organic conductor single crystal at a temperature of 1.9 K, a magnetic field of up to 70 kOe, and in the frequency band between 30 and 120 GHz has been studied. A spectral component due to the cyclotron resonance (CR) of two-dimensional charge carriers has been identified for ν⩾80 GHz and H⩾10 kOe. The effective mass m(ω) increases with the frequency from m≈0.8m ₀ at ν=80 GHz to m≈0.95m ₀ at ν=120 GHz. Measurements of the CR line position and FWHM as functions of frequency yield an independently determined imaginary part of the memory function M(ω), which controls the dynamic magnetoconductivity, and the relaxation time τ(ν=100 GHz)≈2.9×10⁻¹¹ s, which is more than thirty times the value of this parameter in the low-frequency limit τ(ν→0). The anomalous behavior of the CR line position and FWHM is caused by the dispersion of both real and imaginary parts of M(ω), which are probably due to strong Fermi-liquid effects. Zh. éksp. Teor. Fiz. 111, 979–987 (March 1997)     

Magnetic quantum oscillations in the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

The interlayer magnetoresistance of the organic superconductor κ-(BEDT-TTF)₂Cu[N(CN)₂)Br is measured at ambient pressure and under pressures of up to 12.5 kbar. In addition to the slow Shubnikov-de Haas oscillations with a frequency of ≃150 T observed at P⩾5 kbar, rapid oscillations attributed to the magnetic breakdown orbit enveloping an area equal to 100% of the area of the Brillouin zone are found to emerge above B=20 T. The latter oscillations are observed at ambient pressure as well as under pressures of up to 9 kbar. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 190–194 (10 August 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Internal friction in directed-crystallization (Cu-Sn)-Nb alloys

The distinctive features of the low-frequency internal friction Q ⁻¹(T) of (Cu-Sn)-Nb composites at high temperatures (up to 400°C) are investigated for strains in the range 10⁻⁵–10⁻⁴. Considerable hysteresis of Q ⁻¹(T) in the heating-cooling cycle is recorded, including the presence of a minimum at ∼175°C when the sample is heated to 400°C and two peaks P ₂ (at 280°C) and P ₁ (at ∼100°C) when the sample is cooled from 400°C. The activation energy of the anomalous internal friction background (up to 175°C), the oxygen diffusion parameters, and the oxygen concentration in the niobium fibers (all of which govern the peak P ₂) are calculated, and the value and temperature dependence of the yield point of the bronze matrix (which govern the peak P ₁) are estimated. Zh. Tekh. Fiz. 68, 114–117 (November 1998)     

e -μ+→e +μ- process in a model with theSU(2)L×SU(2)R×U(1)B−L gauge group

A model based on theSU(2)_L×SU(2)_R×U(1)_B−L gauge group is used to study the lepton recharging processe ^-μ⁺→e ⁺μ^-. It should be possible to observe this process on a muon collider in the fixed-electron-target regime or the electron-beam regime. It is shown that the given process can be used to measure not only the characteristics of physical Higgs bosons, but also the parameters of neutrino oscillations. Grodno University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 83–88, November, 1998.     

Thermal lensing study and athermal directions in flashlamp-pumped Nd:KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> laser crystal

Thermal lensing has been studied by a probe beam technique in flashlamp-pumped Nd:KGdW laser rods with rod axes positioned in the N _p–N _g plane and making different angles with the N _g optical indicatrix axis. It was found that the orientation of principal meridional planes of the astigmatic thermal lens in Nd:KGdW corresponds to the directions with maximum and minimum values of thermal-expansion coefficient in the plane perpendicular to the rod axis. The athermal Nd:KGdW laser crystal orientation defined as orientation with weak positive near spherical thermal lens has been determined to make an angle of 30^○–40^○ with the N _g axis for light polarization E∥N _m.     

229m Th(3/2+, 3.5 eV) and a check of the exponentiality of the decay law

A new object is proposed for checking the exponentiality of the decay law of an isolated metastable state at long times — the anomalously low-lying level 3/2⁺ (3.5±0.5 eV) in ²²⁹Th. Highly efficient excitation of this level by laser radiation in combination with optimal collection of optical photons emitted in an isomeric transition make it possible to achieve measurement times longer than 50T _1/2. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 521–525 (25 April 1998)     

Determination of the neutron electric form factor from the reaction 3 He(e,e'n) at medium momentum transfer

The electric form factor of the neutron G_En has been determined in double polarized exclusive ³ He(e,e'n) scattering in quasi–elastic kinematics by measuring asymmetries A _⊥, A _∥ of the cross section with respect to helicity reversal of the electron, with the nuclear spin being oriented perpendicular to the momentum transfer q in case of A_⊥ and parallel in case of A_∥. The experiment was performed at the 855 MeV c. w. microtron MAMI at Mainz. The degree of polarization of the electron beam and of the gaseous ³ He target were each about 50%. Scattered electrons and neutrons were detected in coincidence by detector arrays covering large solid angles. Quasi–elastic scattering events were reconstructed from the measured electron scattering angles ϑ_e, φ_e and the neutron momentum vector p _n ^′ in the plane wave impulse approximation. We obtain the result <G _En>_{(0.27 < Q2c2/GeV2 < 0.5)}= 0.0334 ± 0.0033_stat± 0.0028_syst which is averaged over the indicated range of Q ², the squared momentum transfer. This G _En value is significantly smaller than measured from the D(e,e'n) reaction under similar kinematical conditions. To what extent final state interactions in ³He quench the G _En result is subject of calculations currently in progress elsewhere. Received: 29 April 1999     

Contribution of the massive photon decay channel to neutrino cooling of neutron stars

We consider massive photon decay reactions via intermediate states of electron-electron-holes and proton-proton-holes into neutrino-antineutrino pairs in the course of neutron star cooling. These reactions may become operative in hot neutron stars in the region of proton pairing where the photon due to the Higgs-Meissner effect acquires an effective mass m _γ that is small compared to the corresponding plasma frequency. The contribution of these reactions to neutrino emissivity is calculated; it varies with the temperature and the photon mass as T ^3/2 m _γ ^7/2 exp(−m _γ /T) for T<m ^γ . Estimates show that these processes appear as extra efficient cooling channels of neutron stars at temperatures T≅10⁹–10¹⁰ K. Zh. éksp. Teor. Fiz. 114, 385–397 (August 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Oscillation phenomena in polyacetylene: R 1×S 1 Gross-Neveu model with a chemical potential

The phase structure of the two-dimensional Gross-Neveu model in a spacetime of the form R ¹×S ¹ and in the presence of a chemical potential μ is investigated. The phase portrait of the model is constructed in the parameter plane (μ, γ), where γ=1/L and L is the length of the circle S ¹. In the portrait there exist two massive phases, with spontaneously broken chiral invariance, as well as infinitely many massless symmetric phases. Such a vacuum structure leads to oscillations of the critical curve μ _c (γ) of chiral phase transitions. In addition, the particle number density in the vacuum state of the model oscillates if μ<μ _c (γl). Pis’ma Zh. éksp. Teor. Fiz. 68, No. 5, 431–436 (10 September 1998)     

Final results on the search for νμ→νe oscillations in the NOMAD experiment

The results of the search for ν _μ →ν _e oscillations in the NOMAD experiment at CERN are presented. The experiment looked for the appearance of ν _e in a predominantly ν _μ wideband neutrino beam at the CERN SPS. No evidence for oscillations was found. The 90% confidence limits obtained are Δm ²<0.4 eV² for maximal mixing and sin²(2θ)<1.4×10⁻³ for large Δm ². This result excludes the LSND allowed region of oscillation parameters with Δm ²≳10 eV². From Yadernaya Fizika, Vol. 67, No. 11, 2004, pp. 1967–1972. Original English Text Copyright ? 2004 by Popov. This article was submitted by the author in English. The author represents the NOMAD Collaboration     

De Rham complex with ternary differential on the quantum group SL h (2)

In this work, we construct the de Rham complex with the differential operator d satisfying theQ-Leibniz rule, whereQ is a complex number, and the condition d³=0 (ternary differential) on theh-deformed quantum plane in dimension two following the general formalism elaborated in [Bazunova et al.: Czech. J. Phys.51 (2001) 1226]. Then we construct the de Rham complex on the group SL _h (2) which preserves theh-deformed quantum plane by the differentiation of RTT-relations, and, introducing the Maurer-Cartan forms, get an analog of the Maurer-Cartan equation. Presented at the 11th Colloquium “Quantum Groups and Integrable Systems”, Prague, 20–22 June 2002.     

Search for solar axions produced in the p + d → <Superscript>3</Superscript>He + A reaction

A search for the axioelectric absorption of 5.5-MeV solar axions produced in the p + d → ³He + γ (5.5 MeV) reaction was performed with two BGO detectors placed inside a low-background setup. Constraints on the axion-electron coupling constant were obtained for axions with masses in the (0.1–1.0)-MeV range: g _Ae ≤ (1.8–9.0) × 10⁻⁷. The solar positron flux from A → e⁻ + e⁺ decay was determined for axions with masses m _A > 2m _e. Using the existing experimental data on the interplanetary positron flux, a new constraint on the axion-electron coupling constant for axions with masses in the (1.2–5.4)-MeV range was obtained: g _Ae ≤ (1–5) × 10⁻¹⁷.     

Ion transport in the anion-deficient nonstoichiometric phases La0.95(Ba1−x Srx)0.05F2.95 (0⩽x⩽1)

The fluoride-ion conductivity of the nonstoichiometric tysonite phases La_0.95(Ba_1−x Sr_x)_0.05Fe_2.95 (0⩽x⩽1) is investigated by impedance spectroscopy. Electrophysical measurements are performed in the frequency range 5–5×10⁵ Hz and temperature range 300–700 K. A discontinuity is observed in the temperature dependence of the conductivity at T _c=410–430 K. The behavior of the temperature dependence of the electrical conductivity is explained within a transport model taking into account the migration of fluoride ions between different inequivalent structural sites. The maximum value of the conductivity at room temperature (293 K) is 2×10⁻⁴ Ω⁻¹ cm⁻¹ for the solid solution La_0.95Sr_0.05F_2.95. The fluorine-ion conductivity in La_0.95(Ba_1−x Sr_x)_0.05F_2.95 single crystals is almost an order of magnitude larger than the value for the commercial solid electrolyte La_0.992Eu_0.008F_2.992 (a fluorine-selective membrane) having a tysonite structure. Fiz. Tverd. Tela (St. Petersburg) 40, 658–661 (April 1998)     

Quasi-long-range order in the random anisotropy Heisenberg model

The random field and random anisotropy N-vector models are studied with the functional renormalization group in 4−ε dimensions. The random anisotropy Heisenberg (N=3) model has a phase with an infinite correlation length at low temperatures and weak disorder. The correlation function of the magnetization obeys a power law 〈m(r ₁)m(r ₂)〉∼|r ₁−r ₂|^{− 0.62ε}. The magnetic susceptibility diverges at low fields as χ∼H ^−1+0.15ε. In the random field N-vector model the correlation length is finite at arbitrarily weak disorder for any N>3. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 130–135 (25 July 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Distribution of 90° domain reorientations in lead titanate zirconate piezoceramic under longitudinal compression

A static model of a critically polarized ceramic is used to analyze the behavior of the piezocoefficient d ₃₃ of lead titanate zirconate ceramic exposed to a longitudinal compressive stress σ and a quantitative analysis is made of the 90° and 180° domain reorientations. It is shown that for TsTG-83G ceramic a 180° antiparallel domain structure forms at compressive stresses σ>10⁸ N/m². Zh. Tekh. Fiz. 69, 46–49 (June 1999)     

Two-dimensional weak localization effects in high temperature superconductor Nd2−x CexCuO4−δ

A systematic study of the resistivity and Hall effect in single-crystal films Nd_2−x Ce_xCuO_4−δ (0.12⩽x⩽0.20) is presented, with special emphasis on the low-temperature dependence of the normal state conductance. Two-dimensional weak localization effects are found both in a normally conducting underdoped sample (x=0.12) and in situ superconducting optimally doped (x=0.15) or overdoped (x=0.18) samples in a high magnetic field B>B _c2. The phase coherence time τ _ϒ (5.4 · 10⁻¹¹ s at 2 K) and the effective thickness of a CuO₂ conducting layer d (≃1.5Å) have been estimated by fitting 2D weak localization theory expressions to magnetoresistivity data for magnetic fields perpendicular to the ab plane and in plane. Estimates of the parameter d ensure strong carrier confinement and justify a model consisting of almost decoupled 2D metallic sheets for the Nd_2−x Ce_xCuO_4−δ single crystal. Zh. éksp. Teor. Fiz. 116, 1723–1734 (November 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Abelian dyons in the maximal Abelian projection of SU(2) gluodynamics

Correlations of the topological charge Q, the electric current J ^e, and the magnetic current J ^m in SU(2) lattice gauge theory in the maximal Abelian projection are investigated. It is found that the correlator 〈〈QJ ^eJ^m〉〉 is nonzero for a wide range of values of the bare charge. It is shown that: (i) the Abelian monopoles in the maximal Abelian projection are dyons which carry fluctuating electric charge; (ii) the sign of the electric charge e(x) coincides with that of the product of the monopole charge m(x) and the topological charge density Q(x). Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 161–165 (10 February 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.