Tunneling radiative recombination in <Emphasis Type="Italic">p-n</Emphasis> heterostructures based on gallium nitride and other A<Superscript>III</Superscript>B<Superscript>V</Superscript> semiconductor compounds

We present summarized data on the tunneling emission in p-n heterostructures based on GaN and on a series of cubic A^IIIB^V semiconductors, including GaAs, InP, GaSb, and (Ga, In)Sb. The emission in p-n heterostructures of the InGaN/AlGaN/GaN type in a spectral interval from 1.9 to 2.7 eV predominates at small currents (J<0.2 mA). The position of maximum ?ω_max in the spectrum approximately corresponds to the applied potential difference U:?ω_max=eU. The tunneling emission is related to a high electric field strength in GaN-based heterostructures. The radiative recombination probability is higher in the structures with piezoelectric fields. The observed spectra are compared to the spectra of tunneling emission from light-emitting diodes based on GaAs, InP, and GaSb. The experimental results for various semiconductors emitting in a broad energy range (0.5–2.7 eV) are described by the equation ?ω_max=eU=0.5–2.7 eV.     

Absorption spectra of some radiation-doped A<Subscript>3</Subscript>B<Subscript>5</Subscript> compounds

Temperature dependences of the absorption coefficient in A₃B₅ crystals before and after irradiation by electrons with an energy of 6 MeV and a dose of Ф = 2 × 10¹⁷ electron/cm² are studied. A low-lying E_v + 0.4 eV center of a nonimpurity origin is found in both undoped GaAs crystals and those doped with various impurities (Te, Zn, Sn, Ga_1–xIn_xAs, InP, and InP〈Fe〉).     

Fabrication and some properties of ZnO/<Emphasis Type="Italic">A</Emphasis><Superscript>III</Superscript>N heterojunctions

n-ZnO/p-A ^IIIN (A ^III = Ga, Al) heterojunctions have been fabricated, which exhibit relatively strong electroluminescence in the blue-violet spectral range under forward bias. It is shown that ZnO layers grown with rf-discharge activation have a less developed surface with a significant decrease in the sizes and number of zinc clusters. The current-voltage characteristics of the heterostructures obtained have rectifying properties with a cutoff voltage corresponding to the ZnO band gap.     

Mixing of <Emphasis Type="Italic">K</Emphasis><Superscript>0</Superscript> and <Emphasis Type="Italic">B</Emphasis><Superscript>0</Superscript> neutral mesons within the minimum supersymmetry model

Mixing of K ⁰ and B ⁰ mesons is studied in the scope of the minimum supersymmetry model (MSSM) with a type II Yukawa sector and explicit violation of CP invariance in the Higgs potential. The mixing parameters Δm _LS and ? are calculated in the limit of the low-energy four-fermion approximation with a charged Higgs boson exchange. It is shown that supersymmetric effects are very small for K ⁰ mesons and may be quite significant for B _s ⁰ and B _d ⁰ mesons, which imposes constraints on the MSSM parameter space.     

<Emphasis Type="Italic">B</Emphasis>-meson physics: <Emphasis Type="Italic">CP</Emphasis> violation and semileptonic decays

The paper represents a review of our present knowledge on the phenomenology of weak decays of quarks and their role in the determination of the parameters of the Standard Model. Specifically, we focus on CP violation in B decays and the determination of the Cabibbo-Kobayashi-Maskawa matrix element V_cb from exclusive and inclusive semileptonic B decays. We also briefly discuss phenomeno-logical applications concerning the electron energy spectra in inclusive semileptonic B and B_c decays.     

Optical characteristics of radiation from N<Stack><Subscript>2</Subscript><Superscript>*</Superscript></Stack> dimers in a barrier discharge

The spectral and power characteristics of radiation of the second positive system of nitrogen (C ³Π _u → B ³Π _g ) in Ar-N₂ and Ar-N₂-Cl₂ mixtures excited by barrier discharge have been studied experimentally. Addition of argon to N₂ increased the radiation power by sixfold. In the triple mixture Ar-N₂-Cl₂ = 210/0.5/0.005, minor chlorine additions increased the intensity of the C ³Π _u → _B ³Π _g transition by 26% compared to Ar-N₂ mixtures. Radiation power density of 2.7 mW/cm² has been achieved. In both binary and triple mixtures, the second positive system of nitrogen was the major contributor to radiation, while the contributions of the fourth positive system of N ₂ ^* (D ³Σ _u ⁺ → B ³Π _g ), the Vegard-Kaplan transition of N ₂ ^* (A ³Σ _u ⁺ → X ¹Σ _g ⁺ ), and the D′ → A′ band of Cl ₂ ^* were negligibly small.     

<Emphasis Type="Italic">Z</Emphasis><Superscript>0</Superscript>-boson decays in a strong electromagnetic field

The probability of Z ⁰-boson decay to a pair of charged fermions in a strong electromagnetic field, Z ⁰ → \(\bar f\) f, is calculated. On the basis of a method that employs exact solutions to relativistic wave equations for charged particles, an analytic expression for the partial decay width Γ(?) = Γ(Z ⁰ → \(\bar f\) f) is obtained at an arbitrary value of the parameter ? = \(eM_Z^{ - 3} \sqrt { - (F_{\mu \nu } q^\nu )^2 } \), which characterizes the external-field strength. The total Z ⁰-boson decay width in an intense electromagnetic field, Γ _Z (?), is calculated by summing these results over all known generations of charged leptons and quarks. It is found that, in the region of relatively weak fields (? < 0.06), the field-induced corrections to the standard Z ⁰-boson decay width in a vacuum do not exceed 2%. As ? increases, the total decay width Γ _Z (?) develops oscillations against the background of its gradual decrease to the absolute-minimum point. At ?_min = 0.445, the total Z ⁰-boson decay width reaches the minimum value of Γ _Z (?_min) = 2.164 GeV, which is smaller than the Z ⁰-boson decay width in a vacuum by more than 10%. In the region of superstrong fields (? > 1), Γ _Z (?) grows monotonically with increasing external-field strength. In the region ? > 5, the t-quark-production process Z ⁰ → \(\bar t\) t, which is forbidden in the absence of an external field, begins contributing significantly to the total decay width of the Z ⁰ boson.     

High-frequency EPR of Cr<Superscript>2+</Superscript> ions in CdGa<Subscript>2</Subscript>S<Subscript>4</Subscript>

High-frequency broad-band (65–240 GHz) EPR is used to study impurity centers of bivalent chromium in a CdGa₂S₄ crystal. It is found that the EPR spectra correspond to tetragonal symmetry. The spin Hamiltonian H = βB · g · S + B ₂ ⁰ O ₂ ⁰ + B ₄ ⁰ O ₄ ⁰ + B ₄ ⁴ O ₄ ⁴ with the parameters B ₂ ⁰ =23659±2 MHz, B ₄ ⁰ =1.9±1 MHz, |B ₄ ⁴ |=54.2±2 MHz, g_‖=1.93±0.02, and g_⊥=1.99±0.02 is used to describe the observed spectra. It is concluded that chromium ions occupy one of the tetrahedrally coordinated cation positions.     

On screening constants in X-ray spectra

Fresh calculations of the X-ray screening constantsσ ₂ forL _II L _III,M _II M _III andM _IV M _V have been made. It has been found thatσ ₂ is not absolutely constant for differentZ. Some regular variations inσ ₂ with electronic shell structure have been noted.     

Thermal property of binary tetrahedral semiconductors

In this paper we present an expression relating the lattice thermal expansion coefficient α_L (10⁻⁶ K⁻¹) for the A^IIIB^V and A^IIB^VI semiconductors with the product of ionic charges (Z₁Z₂), melting temperature (T_m) and nearest neighbor distance d (Å). The lattice thermal expansion coefficient of these compounds exhibit a linear relationship when plotted on a log–log scale against the melting temperature (T_m), but fall on different straight lines according to the ionic charge product of the compounds. A good agreement has been found between the experimental and calculated values of the lattice thermal expansion coefficient for A^IIIB^V and A^IIB^VI semiconductors.     

QRPA coordinate space calculations of 2<Superscript>+</Superscript> states in <Emphasis Type="Italic">N</Emphasis>=20 isotones

The first 2⁺ states in N=20 isotones are studied within the self-consistent quasiparticle random phase approximation based on the Green’s function method. The residual interaction between quasiparticles with full velocity dependence is consistently derived from the Skyrme interaction plus pairing interaction energy density functional. The B(E2, 0 ₁ ⁺ → 2 ₁ ⁺ ) transition probabilities and the excitation energies of the first 2⁺ states are well described within a single framework. We discuss mainly the microscopic origin of the anomalously large B(E2) value and the very low excitation energy in ³²Mg.     

Synthesis and electrical properties of new perovskite-like <Emphasis Type="Italic">A</Emphasis>Mn<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript> (A = Ca,Ce, and Sm) compounds

AMn₃V₄O₁₂ (A = Ca, Ce, and Sm) compounds with a perovskite structure are synthesized at high pressures and temperatures. The crystalline structure of these compounds (space group \(Im\bar 3\)Z = 2) is determined via X-ray analysis. If ions in the A sublattice are changed in the order Ca²⁺–Sm³⁺–Ce³⁺, the valence is redistributed from Ca²⁺Mn₃²⁺V₄⁴⁺O₁₂ to Sm³⁺Mn₃²⁺V₄^3.75+O₁₂, and to Ce³⁺Mn₃²⁺V₄^3.75+O₁₂. The temperature dependences of the electrical resistivity are studied.     

New measurements on physics of <Emphasis Type="Italic">B</Emphasis>-hadrons in ATLAS experiment

Recent results on B-hadron physics in ATLAS are reviewed. A new measurement of CP-violating parameters in B _s → J/ψφ decay is performed on full Run 1 statistics. Branching fraction BR(B _s → μ⁺μ^?) = (0.9 _?0.8 ^+1.1 )×10^?9 is measured, below the Standard Model (SM) prediction.     

<Emphasis Type="Italic">B</Emphasis>-meson decays into charmonium states in the ATLAS experiment

The paper presents several recent ATLAS results on the analyses of B-meson decays into charmonium states. These include the measurements of B⁺ mass and the fractions of J/ψ mesons produced in b-hadron decays in pp collisions at \(\sqrt s\) = 13 TeV in the center of mass system. The measured partial widths and polarizations in B _c ⁺ → J/ψD _s ^(*)+ decays and CP-violation parameters in B _s ⁰ → J/ψ? decays in pp collisions at 7 and 8 TeV in the center of mass system are also presented.     

Nonstoichiometric high-pressure phase of Tm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

Tm _x Cu₃V₄O₁₂, a perovskite-like oxide (space group, Im-3; Z = 2; a = 7.279–7.293 Å) containing vacancies in its cationic sublattice, was obtained barothermally (P = 7.0–9.0 GPa, t = 1000–1100°C) for the first time. The temperature dependences on the electrical resistivity (10–300 K) and the magnetic susceptibility (0–300 K) were investigated. It was shown that the oxide Tm _x Cu₃V₄O₁₂ is characterized by metal-type conductivity and paramagnetic properties.     

Excitons and Biexcitons in Spheroidal Quantum Dots A<Subscript>2</Subscript>B<Subscript>6</Subscript>

In the limit of strong quantum confinement the lower energy states of excitons and biexcitons in spheroidal quantum dots of semiconductors with a fourfold degenerate vertex of the valence band, which are active in the dipole approximation at one- and two-photon excitation, have been considered. The comparative analysis of the order of energy levels of the hole in the potentials of the infinitely deep quantum well and a three-dimensional harmonic oscillator taking into account the axial anisotropy of the quantum dot (QD) shape is carried out. It is shown that the anisotropy of the QD shape can lead to the opposite sign of splitting with respect to angular momentum projection ±3/2, ±1/2 for spatially odd (1P_3/2) and even (1S_3/2) levels of the hole. At the same time, in the case of the potential of an infinitely deep quantum well, an inversion of the order of 1S_3/2 and 1P_3/2 levels can be observed at values of the ratio of the effective masses of the light and heavy holes β = m_lh/m_hh ≈ 0.14. The type of the trial wave functions of the hole for the state 1P_3/2 in the potential of an isotropic three-dimensional harmonic oscillator depending on β is proposed. The dependence of the binding energy of excitons in the considered potentials on β is presented and the possibility of formation of various biexcitonic states is considered.     

Neutron single-particle structure of <Superscript>48</Superscript>Ca, <Superscript>50</Superscript>Ti, <Superscript>52</Superscript>Cr, <Superscript>54</Superscript>Fe,and <Superscript>56</Superscript>Ni nuclei

The change in the neutron single-particle structure of (1f?2p)-shell magic nuclei near the Fermi energy with an increase in the number of protons in the 1f _7/2 subshell from 0 for ⁴⁸Ca to 8 for ⁵⁶Ni has been investigated. Good agreement of the experimental and estimated values of the single-particle energies E _nlj of the bound states of neutrons in these nuclei with the results of calculations within the dispersive optical model is obtained.     

Exotic molecular states in a strong magnetic field: H<Stack><Subscript>3</Subscript><Superscript>(2+)</Superscript></Stack> ion

The existence of the molecular ion H ₃ ⁽²⁺⁾ in a magnetic field in a triangular and a linear configuration is discussed. A variational method (with an optimization of the form of the vector potential) is used. It is shown that, in the range of magnetic fields 10⁸<B<10¹¹ G, the system (pppe), with the protons forming an equilateral triangle perpendicular to the magnetic line, has a well-pronounced minimum in the total energy. Also, for B?10¹⁰ G, if the protons are situated along a magnetic line (linear configuration), a well-pronounced minimum in the total energy appears. Both configurations are unstable under the decays H(atom) + p + p and H ₂ ⁽⁺⁾ + p. A possible connection between the H ₃ ⁽²⁺⁾ molecular ion and a recently discovered absorption feature in a neutron-star atmosphere is discussed.     

Adiabatic elastic moduli in ZnSe : Mn<Superscript>2+</Superscript> and ZnSe : V<Superscript>2+</Superscript> crystals

The temperature dependences of the elastic moduli C ₄₄ (C ₁₁ ? C ₁₂)/2 and C _l = (C ₁₁ + C ₁₂ + 2C ₄₄)/2 of ZnSe : V²⁺ (impurity concentration, 6 × 10¹⁸ cm^?3) and ZnSe : Mn²⁺ (9.4 × 10²⁰ cm^?3) are measured in the temperature range 1.4–100.0 K at frequencies of 52 and 156 MHz. The temperature dependences of the adiabatic elastic moduli are derived. It is established that softening of the symmetry modules is observed only in the crystal with an impurity having orbitally degenerate states.