Astrophysical <Emphasis Type=Italic>S</Emphasis>-factor of radiative <Emphasis Type=Italic>p</Emphasis><Superscript>6</Superscript>Li capture at low energies

A possibility of describing experimental data for the astrophysical S-factor of p⁶Li capture at low energies is discussed within the potential cluster model with forbidden states.     

Anisotropic distributions of electrical currents in high-<Emphasis Type=Italic>T</Emphasis><Subscript><Emphasis Type=Italic>c</Emphasis></Subscript> grain-boundary junctions

We developed a self-consistent method for the calculation of spatial current distributions in high-T _c grain-boundary junctions. It is found that crystallographic anisotropy of high-T _c superconducting electrodes results in the effects, which previously were not taken into account for interpretations of experimental data. Among them is a significant redistribution of electrical currents in superconducting electrodes in the vicinity of a grain boundary. In particular in the case of [100]-tilt bicrystal junctions, this current redistribution results in a substantial focusing to the top or bottom part of a thickness of the grain boundary, depending on “roof”- or “valley”-type of the grain boundary. This redistribution is accompanied by generation of vortex currents around the grain boundary, which leads to self-biasing of grain-boundary junctions by magnetic field nucleated by these vortex currents. It is shown that twinning or variation of geometrical shape of the high-T _c electrode may also result in intensive redistribution of electrical currents and nucleation of local magnetic fields inside a high-T _c superconducting electrodes.     

An ARPES view on the high-<Emphasis Type=Italic>T</Emphasis><Subscript>c</Subscript> problem: Phonons <Emphasis Type=Italic>vs.</Emphasis> spin-fluctuations

We review the search for a mediator of high-T _c superconductivity focusing on ARPES experiment. In case of HTSC cuprates, we summarize and discuss a consistent view of electronic interactions that provides natural explanation of both the origin of the pseudogap state and the mechanism for high temperature superconductivity. Within this scenario, the spin-fluctuations play a decisive role in formation of the fermionic excitation spectrum in the normal state and are sufficient to explain the high transition temperatures to the superconducting state while the pseudogap phenomenon is a consequence of a Peierls-type intrinsic instability of electronic system to formation of an incommensurate density wave. On the other hand, a similar analysis being applied to the iron pnictides reveals especially strong electron-phonon coupling that suggests important role of phonons for high-T _c superconductivity in pnictides.     

GaSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript><Emphasis Type="Italic">S</Emphasis><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solutions

The most probable parameters of the pure, doped, and mixed GaSe_1−xS_x (x ≤ 0.4) crystals (solid solutions) are presented together with the results of investigations of their crystal structure and defects, optical and mechanical properties, and damage thresholds. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 35–40, June, 2007.     

<Emphasis Type=Italic>Y</Emphasis> and <Emphasis Type=Italic>Z</Emphasis> luminescence of polycrystalline cadmium telluride

The properties of polycrystalline CdTe with a grain size of 5–30 μm have been investigated using the microphotoluminescence methods of spectral analysis and topography. This material has been prepared by direct synthesis in a vapor flow of components at a low temperature. The dominance of the Y and Z bands in the spectra reflects a nonequilibrium character of the crystallization processes. The superlinear dependences of the luminescence intensity on the level of the band-to-band excitation indicate the exciton nature of the corresponding transitions. The activation energies for temperature quenching of luminescence in the temperature range T = 100–150 K are found to be 120 meV for the Y luminescence and 180 meV for the Z luminescence, which correspond to the dissociation of excitons bound to defects with the transition of charge carriers to the conduction and valence bands. The monochromatic topography data indicate that Y and Z defects have different material bases.     

The determination of <Emphasis Type="Italic">α</Emphasis><Subscript><Emphasis Type="Italic">S</Emphasis></Subscript> from <Emphasis Type="Italic">τ</Emphasis> decays revisited

We revisit the determination of α _S (m _τ ²) using a fit to inclusive τ hadronic spectral moments in light of (1) the recent calculation of the fourth-order perturbative coefficient K ₄ in the expansion of the Adler function, (2) new precision measurements from BABAR of e⁺e⁻ annihilation cross sections, which decrease the uncertainty in the separation of vector and axial-vector spectral functions, and (3) improved results from BABAR and Belle on τ branching fractions involving kaons. We estimate that the fourth-order perturbative prediction reduces the theoretical uncertainty, introduced by the truncation of the series, by 20% with respect to earlier determinations. We discuss to some detail the perturbative prediction of two different methods: fixed-order perturbation theory (FOPT) and contour-improved perturbative theory (CIPT). The corresponding theoretical uncertainties are studied at the τ and Z mass scales. The CIPT method is found to be more stable with respect to the missing higher order contributions and to renormalization scale variations. It is also shown that FOPT suffers from convergence problems along the complex integration contour. Nonperturbative contributions extracted from the most inclusive fit are small, in agreement with earlier determinations. Systematic effects from quark-hadron duality violation are estimated with simple models and found to be within the quoted systematic errors. The fit based on CIPT gives α _S (m _τ ²)=0.344±0.005±0.007, where the first error is experimental and the second theoretical. After evolution to M _Z we obtain α _S (M _Z ²)=0.1212±0.0005±0.0008±0.0005, where the errors are respectively experimental, theoretical and due to the evolution. The result is in agreement with the corresponding N³LO value derived from essentially the Z width in the global electroweak fit. The α _S (M _Z ²) determination from τ decays is the most precise one to date.     

Unitarity of the tree approximation to the Glauber <Emphasis Type=Italic>AA</Emphasis> amplitude for large <Emphasis Type=Italic>A</Emphasis>

The nucleus-nucleus Glauber amplitude in the tree approximation is studied for heavy participant nuclei. It is shown that, contrary to previous published results, it is not unitary for realistic values of nucleon-nucleon cross sections.     

Structure and spectral properties of truxene dye <Emphasis Type=Italic>S</Emphasis>5

On the ground of functional theory with the B3LYP and BMK functionals, we have studied the structure and optical properties of a truxene dye sensitizer S5 for photoelectric transducers. Based on the calculations of the vertical excitations energy of the dye molecule and accounting the influence of the solvent, we have revealed a positive solvatochromic effect that is weak compared to results obtained in the vacuum approximation. We have studied new features describing stabilization of the planar structure of the cyanothiophene-acrylic fragment of the S5 dye.