Normal-metal hot-electron bolometer with Andreev reflection from superconductor boundaries

This paper describes the design and experimental testing of a high-sensitivity hot-electron bolometer based a film of normal metal, exploiting the Andreev reflection from superconductor boundaries, and cooled with the help of a superconductor-insulator-normal metal junction. At the measured thermal conductivity, G≈6×10⁻¹² W/K, and a time constant of τ=0.2 μs, and a temperature of 300 mK, the estimated noise-equivalent power NEP=5×10⁻¹⁸ W/Hz^1/2, assuming that temperature fluctuations are the major source of noise. At a temperature of 100 mK, the thermal conductivity drops to G≈7×10⁻¹⁴ W/K, which yields NEP=2×10⁻¹⁹ W/Hz^1/2 at a time constant of τ=5 μs. The microbolometer has been designed to serve as a detector of millimeter and FIR waves in space-based radio telescopes. Zh. éksp. Teor. Fiz. 115, 1085–1092 (March 1999)     

Perturbation of atomic energy levels by a metal surface

The energy level shifts of one-electron atomic particles H, He⁺, Li⁺⁺, etc. which interact with a metal surface have been investigated. In the approximation of image charges, an operator describing perturbations of atomic levels has been obtained. By numerically solving the Schro dinger equation, we have calculated energy levels of H(1s), H*(n=2), and C⁵⁺(n) as functions of the distance between an atom and surface. Asymptotic behavior of atomic levels at large distances from the surface has been studied. The linear Stark effect for excited states, which was earlier mentioned by A. V. Chaplik, has been found and investigated in detail. Zh. éksp. Teor. Fiz. 116, 236–256 (July 1999)     

Matrix element of the anomalously low-energy (3.5±0.5 eV) transition in 229Th and the isomer lifetime

The matrix element of the anomalously low-energy (3.5±0.5 eV) nuclear M1 transition between the first excited state and the ground state of the ²²⁹Th nucleus is determined with allowance for the Coriolis mixing of the rotational bands. The upper and lower limits on the lifetime of the level with respect to an isomeric transition are given. A method is proposed for measuring the half-life of the low-lying isomer ^229m Th directly in a ²³³U sample. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 4, 233–238 (25 February 1998)     

Alpha decay of the first excited state of the Th-229 nucleus

The α decay of the anomalously low-lying isomeric level 3/2⁺ (3.5±1.0 eV) of the ²²⁹Th nucleus is studied. The lifetime of the isomer with respect to a decay is predicted and the spectrum of the emitted a particles is calculated. It is noted that the complete α spectrum of the isomer and accelerated α decay of ²²⁹Th can be observed by exciting the nuclei with laser radiation. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 319–323 (10 September 1996)     

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)     

Spin exchange and chemi-ionization during collisions of polarized metastable helium atoms with ground-state cesium atoms

The kinetics of the optical orientation of atoms in a helium-cesium gas-discharge plasma are considered, and kinetic equations describing the optical orientation of atoms in the case of two simultaneously occurring processes, viz., an elastic process (spin exchange) and an inelastic process (chemi-ionization), are derived. The rate constants of these processes are determined experimentally: C _se=(2.8±0.8)×10⁻⁹ cm³s⁻¹, C _ci=(1.0±0.3)×10⁻⁹ cm³s⁻¹. Zh. Tekh. Fiz. 69, 36–40 (September 1999)     

Fine structure of splitting of the separatrix of a nonlinear resonance

This report is a continuation of an analysis, initiated elsewhere V.V. Vecheslavov and B. V. Chirikov, Zh. éksp. Teor. Fiz. 114, 1516 (1998) [JETP 86, 823 (1998)], of the effect of splitting of the separatrix of a nonlinear resonance for the model of standard mapping, based on results of direct measurements of the splitting angle α(K), where K is the system parameter. Measurements were made in the previously used wide range 0.1≳α≳10⁻²⁰⁸ (1⩾K⩾0.0004), but with significantly higher relative (better than 10⁵⁰) and average (∼10⁻⁵⁵) accuracy. This procedure made it possible to substantially refine the effects observed in Ref. 1 and construct qualitatively new empirical dependences providing reliable extrapolation of the data obtained for the angle and the invariant in the intermediate asymptotic limit K≲10⁻² beyond the limits of the investigated region. The results obtained by us can be useful for further development of the theory of separatrix splitting and formation of the stochastic layer of a nonlinear resonance. Zh. éksp. Teor. Fiz. 116, 336–346 (July 1999)     

Raman scattering in a near-surface n-GaAs layer implanted with boron ions

Structure in the Raman scattering spectra of near-surface n-GaAs layers (n=2×10¹⁸ cm⁻³) implanted with 100 keV B⁺ ions in the dose range 3.1×10¹¹–1.2×10¹⁴ cm⁻² is investigated. The qualitative and quantitative data on the carrier density and mobility and on the degree of amorphization of the crystal lattice and the parameters of the nanocrystalline phase as a result of ion implantation are obtained using a method proposed for analyzing room-temperature Raman spectra. Fiz. Tverd. Tela (St. Petersburg) 41, 1495–1498 (August 1999)     

Design and Synthesis of Highly Photostable Yellow–Green Emitting 1,8-Naphthalimides as Fluorescent Sensors for Metal Cations and Protons

Two highly photostable yellow–green emitting 1,8-naphthalimides 5 and 6, containing both N-linked hindered amine moiety and a secondary or tertiary cation receptor, were synthesized for the first time. Novel compounds were configured as “fluorophore–spacer–receptor” systems based on photoinduced electron transfer. Photophysical characteristics of the dyes were investigated in DMF and water/DMF (4:1, v/v) solution. The ability of the new compounds to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions (Cu²⁺, Pb²⁺, Zn²⁺, Ni²⁺, Co²⁺) and protons. The presence of metal ions and protons was found to disallow a photoinduced electron transfer leading to an enhancement in the dye fluorescence intensity. Compound 5, containing secondary amine receptor, displayed a good sensor activity towards metal ions and protons. However the sensor activity of dye 6, containing a tertiary amine receptor and a shorter hydrocarbon spacer, was substantially higher. The results obtained indicate the potential of the novel compounds as highly photostable and efficient “off–on” pH switchers and fluorescent detectors for metal ions with pronounced selectivity towards Cu²⁺ ions.     

Feasibility of measuring the average sizes of diamagnetic domains by the μSR 2 method

Abtract One of the simplest examples of possible application of the μSR ² method for estimating the sizes of diamagnetic domains is analyzed in detail. The domains have been observed for the first time by means of the μ SR method in beryllium [G. Solt, C. Baines, V. S. Egorov et al., Hyperfine Interactions 104, 257 (1997)]. Results are given from a computer simulation of a μSR ² experiment to measure domain sizes in Be. An algorithm is described for processing the experimental results. It is graphically demonstrated that domain sizes can be estimated within the accelerator operating time allocated for an ordinary μSR experiment. Zh. éksp. Teor. Fiz. 115, 2133–2142 (June 1999)     

Carrier mobility contribution to the piezoresistive effect in SmS

A study is reported of the contribution to the piezoresistive effect in samarium-monosulfide-based materials by pressure-induced variation of carrier mobility. As follows from calculations and experimental data, the piezoresistance coefficient for hydrostatic pressure cannot exceed 7×10⁻³ MPa⁻¹ at T=300 K. Fiz. Tverd. Tela (St. Petersburg) 41, 1963–1964 (November 1999)     

Induced emission from a sodium Rydberg atom in a microwave cavity

Results are presented from an experiment on the observation of an induced microwave transition 37P-37S in sodium Rydberg atoms under the action of 30 thermal photons in a microwave cavity. The measured value of the transition rate (4±1.5)×10⁴ s⁻¹ agrees with the calculated value. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 6, 413–416 (25 March 1999)     

The aγγγ vertex and three-photon axion decay in an external magnetic field

The axion vertex aγγγ, the probability of three-photon axion decay in an external magnetic field, and the cross section of the crossing process aγ→2γ, which CP invariance forbids in vacuum, are calculated for the first time. It is shown that in superstrong magnetic fields B≫F ₀=m ²/|e|=4.41·10¹³ G the probability of three-photon decay is greater than the probability of two-photon decay. The astrophysical aspects of the questions examined are discussed. Zh. éksp. Teor. Fiz. 116, 26–34 (July 1999)     

Predicted existence of H 3 ++ molecular ions in strong magnetic fields

It is shown by a variational method that the molecular ion H ₃ ⁺⁺ can exist for magnetic fields B< 10¹¹ G. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 800–805 (10 June 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Logarithmic temperature dependence of the conductivity of the two-dimensional metal

We report on the first observation and studies of a weak delocalizing logarithmic temperature dependence of the conductivity, which causes the conductivity of the 2D metal to increase as T decreases down to 16 mK. The prefactor of the logarithmic dependence is found to decrease gradually with density, to vanish at a critical density n _c , 2∼2×10¹² cm⁻², and then to have the opposite sign at n>n _c ,2. The second critical density sets the upper limit on the existence region of the 2D metal, whereas the conductivity at the critical point, G _c ,2∼120e ²/h, sets an upper (low-temperature) limit on its conductivity. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 497–501 (25 September 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Spin-spin interaction of Ni2+ ions in ZnSiF6·6H2O

The angular dependences of the electron spin resonance spectrum of 1% Ni²⁺ ions in a ZnSiF₆·6H₂O matrix are investigated experimentally at 36 GHz and 4.2 K. Besides the main spectrum of the isolated ion, we observed a spectrum due to interacting pairs of Ni²⁺ ions, located in the first (nn) and second (2n) coordination spheres and coupled by, besides the magnetic dipole-dipole interaction, isotropic exchange: J _nn = (−197±1)×10⁻⁴, J _2nα = (−5±1)×10⁻⁴, and J _2nβ = (3±2)×10⁻⁴ cm⁻¹. Lines due to other isolated Ni²⁺ ions, which have a different initial splitting D, are also present in the spectrum with intensity comparable to the pair spectrum. Low-symmetry distortions of the crystal field are observed, caused by a pair of impurity ions located close to one another. It is shown that the previously proposed interpretation is incorrect. Fiz. Tverd. Tela (St. Petersburg) 41, 1602–1608 (September 1999)     

Anomalous Hall effect in granular Fe/SiO2 films in the tunneling-conduction regime

It is established that the Hall effect in Fe/SiO₂ nanocomposite films in the activational tunneling conduction range is anomalous, i.e., the Hall resistivity ρ_h is proportional to the magnetization and is due to the spin-orbit interaction. The parametric coupling of the Hall and longitudinal (ρ_xx) resistances ρ_h ∝ ρ _xx ^m (with temperature as the parameter) is characterized by a much lower value of the exponent m than in a uniform ferromagnetic metal. This circumstance is attributed to the characteristic features of the Hall effect mechanism in the hopping regime — in our case, the interference of the amplitudes of tunneling transitions in a set of three granules. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 87–92 (25 July 1999)     

Identification of extragalactic cosmic-ray sources using data from various detection facilities

Showers with energies E>3.2×10¹⁹ eV and E≥10²⁰ eV detected at the AGASA (Akeno, Japan), Haverah Park, and Yakutsk arrays are investigated. The question of how the identification of sources depends on the error in determining the shower arrival directions is analyzed. Confirmation is obtained for the conclusion in the author’s earlier work, that the principal sources of shower-driven particles are Seyfert galaxies with red shifts z≤0.0092, which are weak emitters in the x-ray and radio ranges. Zh. éksp. Teor. Fiz. 116, 1121–1130 (October 1999)     

Contribution to the theory of the ferromagnetism of metals with a hexagonal close-packed lattice

The possibility of the appearance of ferromagnetic instability in a hexagonal close-packed system is established on the basis of the idea of a strong interaction in the same unit cell. The conditions for the appearance of spin and orbital instability as a function of the degree of filling of the 2xy, x ²−y ² shell are obtained. The physical picture obtained has a direct relationship to ferromagnetism of hexagonal and cubic cobalt, which possesses the highest Curie temperature, 1396 K. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 7, 451–456 (10 October 1999)     

Donaldson Invariants of Product Ruled Surfaces¶and Two-Dimensional Gauge Theories

Using the u-plane integral of Moore and Witten, we derive a simple expression for the Donaldson invariants of product ruled surfaces Σ _g ×S ², where Σ _g is a Riemann surface of genus g. This expression generalizes a theorem of Morgan and Szabó for g=1 to any genus g. We give two applications of our results: (1) We derive Thaddeus' formulae for the intersection pairings on the moduli space of rank two stable bundles over a Riemann surface. (2) We derive the eigenvalue spectrum of the Fukaya–Floer cohomology of Σ _g ×S ¹. Received: 22 July 1999 / Accepted: 12 June 2000