Lattice instability induced by 3<Emphasis Type="Italic">d</Emphasis> impurities in II–VI compound semiconductors

Nickel-impurity-induced transverse displacements of ions in a Zn_1?xNi_xSe lattice (x = 0.0025) were detected. This type of displacement correlates with macroscopic distortions of a crystal associated with transverse ultrasonic waves that are propagated along the 〈110〉 direction. The shear instability is assumed to be due to the hybridization of the sp³ bonds with the 3d states of the impurity centers.     

Anomalous hall effect in a diluted <Emphasis Type="Italic">p</Emphasis>-InAs〈Mn〉 magnetic semiconductor

The dependences of the electrical resistivity and the Hall coefficient of single-crystal p-InAs〈Mn〉 bulk samples with an acceptor concentration of about 10¹⁸ cm^–3 on uniform pressure P = 4–6 GPa at T = 300 K in the region of impurity conduction are quantitatively analyzed. The anomalous Hall effect is shown to occur in p-InAs〈Mn〉. Its contribution is negative and correlates with the deionization of acceptors and an increase in the magnetic susceptibility.     

Partial virial theorems for atomic-molecular systems

New virial relations for three-and four-particle atomic-molecular systems are proposed. Using operators of extension or squeezing of interparticle distances, it is shown that, for all pairs of j and k particles in S states of these systems, the following partial virial relations are valid: 〈2T _jk 〉+〈 V _jk 〉=0, where 〈V _jk 〉 is the average Coulomb interaction energy for a pair of particles and 〈T _jk 〉 is a part of the average kinetic energy of the system. There are three and six such relations for three-and four-particle systems, respectively. The conventional virial theorem (〈 2T〉+〈V〉=0) for the average total kinetic and potential energies of the system (〈 T〉 and 〈V〉, respectively) corresponds to the summation of partial virial relations over all pairs of particles. It is shown by an example of variational calculations of the helium atom ⁴He²⁺ e ^? e ^? and the helium muon-electron mesoatom ⁴He²⁺μ^? e ^? that partial virial relations are a highly sensitive indicator of the accuracy of wave functions.     

Gottfried Sum Rule in QCD Nonsinglet Analysis of DIS Fixed-Target Data

Deep-inelastic-scattering data from fixed-target experiments on the structure function F₂ were analyzed in the valence-quark approximation at the next-to-next-to-leading-order accuracy level in the strong-coupling constant. In this analysis, parton distributions were parametrized by employing information from the Gottfried sum rule. The strong-coupling constant was found to be α _s (M²_Z) = 0.1180 ± 0.0020 (total expt. error), which is in perfect agreement with the world-averaged value from an updated Particle Data Group (PDG) report, α^PDG _s (M²_Z) = 0.1181 ± 0.0011. Also, the value of 〈x〉_u?d = 0.187 ± 0.021 found for the second moment of the difference in the u- and d-quark distributions complies very well with the most recent lattice result 〈x〉^LATTICE_u?d = 0.208 ± 0.024.     

Dependence of the Daily <Emphasis Type="Italic">N</Emphasis><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript>F2 Values over Mid-Latitude Stations on the Solar and Geomagnetic Activity

The results of studies of the dependence of the daily electron concentration at maximum of the F2 ionospheric layer in January 2008–2015 on the solar and geomagnetic activity are presented. The solar radio emission flux density indices F_10.7 and geomagnetic activity indices A _p were averaged over 27 days, and 〈F_10.7〉₂₇ and 〈A _p 〉₂₇, respectively, were obtained. Based on the data of three stations, 27-day median (with the middle of January 15) daily N _m F2 variations were obtained for 2008–2015. Based on these data, the following paradox was discovered: in January 2014, when the values of the solar activity index F_10.7 were larger than in 2015, the dailyN _m F2 values were smaller. Averaging over four hours of local daytime (10:00–14:00 LT) gave the daily average January 〈N _m F2〉 values for each selected station for each year. To solve this paradox, a double linear regression of 〈N _m F2〉 on 〈F_10.7〉₂₇ and 〈A _p 〉₂₇ was constructed. Due to this, it was concluded that the contribution of geomagnetic activity to daily January 〈N _m F2〉 values is positive. A comparison of the mean square errors of the linear and double linear regressions for 〈F_10.7〉₂₇ and 〈F_10.7〉₈₁ showed that the use of 〈F_10.7〉₂₇ led to smaller errors than the use of 〈F_10.7〉₈₁.     

A study of the nuclear-medium influence on transverse momentum of hadrons produced in deep-inelastic neutrino scattering

The influence of nuclear effects on the transverse momentum (p_T) of neutrino-produced hadrons is investigated using the data obtained with the SKAT propane-freon bubble chamber irradiated in the neutrino beam (with E _v =3–30 GeV) at the Serpukhov accelerator. It has been observed that the nuclear effects cause an enhancement of 〈p _T ² 〉 of hadrons produced in the target fragmentation region at low invariant mass of the hadronic system (2 < W < 4 GeV) and at low energies transferred to the hadrons (2 < ν < 9 GeV). At higher W and ν, no influence of nuclear effects on 〈p _T ² 〉 is observed. Measurement results are compared with predictions of a simple model, incorporating secondary intranuclear interactions of hadrons, which qualitatively reproduces the main features of the data.     

Mechanism of charge transfer in <Emphasis Type="Italic">n</Emphasis>-CdS/<Emphasis Type="Italic">p</Emphasis>-CdTe heterojunctions

The capacitance-voltage and current-voltage characteristics of the n-CdS/p-CdTe heterosystem are investigated. Analysis of these characteristics demonstrates that the CdTe_1?x S _x solid solution formed at the n-CdS/p-CdTe heterointerface is inhomogeneous in both the conductivity and composition. The thickness of solid solutions is estimated from the capacitance-voltage characteristics. It is shown that, for the n-CdS/p-CdTe heterosystem, the current-voltage characteristic in the current density range 10^?8-10^?5 A cm^?2 is governed by the thermal electron emission, whereas the current in the heterostructure at current densities in the range 10^?4-10^?2 A cm^?2 is limited by recombination of charge carriers in the electroneutral region of the CdTe_1?x S _x solid solution. The lifetime and the diffusion length of minority charge carriers in the CdTe_1?x S _x solid solution and the surface recombination rate at the interface between the CdS layer and the CdTe_1?x S _x solid solution are determined. It is demonstrated that the n-CdS/p-CdTe heterostructure operates as a p-i-n structure in which CdTe is a p layer, CdTe_1?x S _x is an i layer, and CdS is an n layer.     

On a Semiclassical Formula for Non-Diagonal Matrix Elements

Let H(?)=?? ²d²/dx ²+V(x) be a Schrödinger operator on the real line, W(x) be a bounded observable depending only on the coordinate and k be a fixed integer. Suppose that an energy level E intersects the potential V(x) in exactly two turning points and lies below V _∞=lim?inf?_|x|→∞ V(x). We consider the semiclassical limit n→∞, ?=? _n →0 and E _n =E where E _n is the nth eigenenergy of H(?). An asymptotic formula for 〈n|W(x)|n+k〉, the non-diagonal matrix elements of W(x) in the eigenbasis of H(?), has been known in the theoretical physics for a long time. Here it is proved in a mathematically rigorous manner.     

Non-extensivity of the chemical potential of polymer melts

Following Flory’s ideality hypothesis, the chemical potential of a test chain of length n immersed into a dense solution of chemically identical polymers of length distribution P(N) is extensive in n . We argue that an additional contribution \( \delta\) \( \mu_{{{\rm c}}}^{}\)(n) ～ +1/\( \rho\) \( \sqrt{{n}}\) arises (\( \rho\) being the monomer density) for all P(N) if n ? 〈N〉 which can be traced back to the overall incompressibility of the solution leading to a long-range repulsion between monomers. Focusing on Flory-distributed melts, we obtain \( \delta\) \( \mu_{{{\rm c}}}^{}\)(n) \( \approx\) (1 - 2n/〈N〉)/\( \rho\) \( \sqrt{{n}}\) for n ? 〈N〉² , hence, \( \delta\) \( \mu_{{{\rm c}}}^{}\)(n) \( \approx\) -1/\( \rho\) \( \sqrt{{n}}\) if n is similar to the typical length of the bath 〈N〉 . Similar results are obtained for monodisperse solutions. Our perturbation calculations are checked numerically by analyzing the annealed length distribution P(N) of linear equilibrium polymers generated by Monte Carlo simulation of the bond fluctuation model. As predicted we find, e.g., the non-exponentiality parameter K _p \( \equiv\) 1 - 〈N ^p〉/p!〈N〉^p to decay as K _p \( \approx\) 1/\( \sqrt{{\langle N \rangle }}\) for all moments p of the distribution.     

A study of the neutrino production of <Emphasis Type="Italic">φ</Emphasis> and <Emphasis Type="Italic">D</Emphasis><Stack><Subscript><Emphasis Type="Italic">s</Emphasis></Subscript><Superscript>+</Superscript></Stack> mesons

The charged current neutrino production of φ and D _s ⁺ mesons is studied, using the data obtained with the SKAT bubble chamber exposed to the Serpukhov accelerator neutrino beam. It is found that the φ production occurs predominantly in the forward hemisphere of the hadronic c.m.s. (at x _F > 0, x _F being the Feynman variable), with the mean yield strongly exceeding the expected yield of directly produced φ mesons and varying from 〈n _φ(x _F s 0)〉 = (0.92 ± 0.34) × 10^?2 at W > 2 GeV up to (1.23 ± 0.53) × 10^?2 at W > 2.6 GeV and (1.44 ± 0.69) × 10^?2 at W > 2.9 GeV, W being the invariant mass of the hadronic system. For the first time, the inclusive yield of leading D _s ⁺ mesons carrying more than z = 0.85 of the current c-quark energy is estimated: 〈n _{D s} ⁺ (z > 0.85, W > 2.9 GeV)〉 = (6.64 ± 1.91) × 10^?2. It is shown that the shape of measured φ meson differential spectrum on xF is reproduced by that expected from the D _s ⁺ → φX decays. An indication was obtained that this expected spectrum underestimates the measured φ yield.     

Josephson effects in unconventional heavy fermion superconductors

We discuss the Josephson effect for pairing states which break crystal symmetries in addition to gauge symmetry. We consider theE _1g andE _2u models for the low-temperature phase ofUPt ₃, with order parameters Δ(E _1g )～p _z (p _x +ip _y ) and Δ(E _2u )～p _z (p _x +ip _y )². We report calculations of Josephson critical currents, taking into account the effects of depairing at the interface. For singlet-triplet junctions the critical current is non-zero only for spin-orbit, spin-flip tunneling, and is found to be much smaller than the Ambegaokar-Baratoff value even when the spin-orbit tunneling amplitude is comparable to the spin-independent amplitude.     

Magnetization and Static Magnetic Susceptibility of Fine-Crystalline High-Temperature YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Superconductors Synthesized by the Sol–Gel Method

A comparative study of the magnetization and static magnetic susceptibility of high-temperature superconductors (HTSC) YBa₂Cu₃O_y synthesized by two variants of the sol–gel method with different average sizes of crystallites 〈 D〉 ranging 0.4–2 μm has been performed in constant magnetic fields (Н ≤ 6 kOe). It has been shown that the different annealing temperatures and times, at which their crystal structure is formed, change both the average sizes of crystallites 〈D〉 and the sizes of the structural homogeneity regions 〈l〉 and, at the same time, the magnetic field penetration depth (λ) and the coherence length (ξ). As a result, such parameters as 〈D〉 ~ λ and 〈l〉 ~ ξ become comparable, leading to a change in the physical characteristics of HTSCs. It has also been shown that the superconducting transition temperature T_c determined from the measurements of magnetic characteristics in constant magnetic fields remains within values optimal for superconductivity (T_c ≈ 92 K) in the case of an optimal number (y) of oxygen atoms, which determine the levels of charge doping for a given compound.     

Properties of proton clusters in inelastic CC interactions accompanied by the production of Λ and <Emphasis Type="Italic">K</Emphasis><Superscript>0</Superscript> particles at <Emphasis Type="Italic">p</Emphasis> = 4.2 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon

Within a new relativistically invariant approach, the properties of proton clusters that are formed together with Λ and K⁰ particles in inelastic CC interactions at p=4.2 GeV/c per nucleon are investigated in the space of relative 4-velocities. The observed proton clusters are shown to be characterized by high values of the mean kinetic energy of the protons in the cluster rest frame: 〈T _p 〉=100±2 MeV.     

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〉).     

Structural and magnetic phase transformations in the BiFeO<Subscript>3</Subscript>-CaFe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> system

The crystal structure and magnetic properties of the Bi_{1 ? x} Ca _x Fe_{1 ? x/2}Nb _x/2O₃ system were studied. It is shown that, at x ≤ 0.15, the unit-cell symmetry of solid solutions is rhombohedral (space group R3c). Solid solutions with x ≥ 0.3 have an orthorhombic unit cell (space group Pbnm). The rhombohedral compositions are antiferromagnetic, while the orthorhombic compositions exhibit a small spontaneous magnetization due to Dzyaloshinski?-Moriya interaction. In CaFe_0.5Nb_0.5O₃, the Fe³⁺ and Nb⁵⁺ ions are partially ordered and the unit cell is monoclinic (space group P2₁/n). In the concentration range 0.15 < x < 0.30, a two-phase state (R3c + Pbnm) is revealed.     

Study of collective flow effects in CC collisions at a momentum of 4.2 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon

Directed (in-plane) flows of protons, pions, and projectile light fragments (d, t, ³He, ⁴He) have been observed by investigating the dependence of the mean transverse momentum in the reaction plane 〈p _x 〉 on the rapidity y in the c.m. system for CC collisions at a momentum of 4.2 GeV/c per nucleon. The comparison of our in-plane-flow results of protons with flow data for various projectile/target configurations was made using the scaled flow F _s = F/(A _P ^1/3 + A _T ^1/3 ). F _s demonstrates a common scaling behavior for flow values from different systems. From azimuthal distributions of protons and π^? mesons, out-of-plane (squeeze-out) flow effects have been observed and the parameter a₂ (the measure of the anisotropic emission strength) has been extracted. The quark-gluon string model reproduces the experimental results quite well.     

Scaling of semi-inclusive events in <Emphasis Type="Italic">pp</Emphasis> interactions

The normalized single-particle semi-inclusive double-differential spectrum of π^t- mesons from pp interactions at 6.6–400 GeV/c and the relative concentration of π⁰ and K _S ⁰ mesons in such events of fixed multiplicity of π^? mesons are completely determined by specifying any feature of this spectrum—for example, 〈y²〉 _n or 〈E〉 _n . Therefore, a two-parameter sample of semi-inclusive events that depends on the energy and the multiplicity reduces to a one-parameter sample.     

Raman scattering and optical normal vibrations of the Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript>x</Subscript>Se crystal lattice

The nonresonant spectra of the Raman scattering in Zn_1?xCd_xSe crystals (0≤ x≤1) are investigated. The mode doublet was found to gradually shift with increasing x from the longitudinal-transverse frequencies of ZnSe to the longitudinal-transverse frequencies of CdSe. Furthermore, an additional branch of weak modes was observed between the doublet components. The frequencies of this branch are shown to correspond to the frequencies of the cadmium impurity vibrations in the ZnSe lattice at x=0 and the zinc impurity vibrations in the CdSe lattice at x=1. The concentration dependences of the modes and atomic displacements are analyzed by using the isodisplacement model that includes the interaction between ZnSe-and CdSe-like vibrations. It is concluded that a one-mode behavior with the formation of an additional weak branch in the longitudinal-transverse splitting region is characteristic of this system.     

Electron localization during an electronic-topological transition in Mo-Re alloys

Oscillations in the superconducting transition temperature ΔT _c (P), in the critical magnetic field ΔH _c (P), in the thermopower α / T (T ²), and in electrical resistivity ρ(T) (P is pressure) of Mo_1?x -Re _x alloys are observed at low temperatures against the background of specific features related to an electronic-topological transition (ETT) in these alloys. The oscillations are sensitive to the impurity concentration: they increase when the Re impurity concentration is close to the critical concentration C _c at which the ETT occurs. Oscillations are also detected in the concentration dependences of the temperature coefficient of resistivity (?ρ / ?T (C)) and the thermopower derivative (?(α/T) / ?T ² (C)) of Mo_1?x -Re _x alloys at low temperatures. The former and latter oscillations are shown to correlate with each other. These specific features are assumed to result from the ETT and to be related to the localization of the part of the electrons that fill a new cavity in the Fermi surface during this transition.     

Electron paramagnetic resonance in mixed crystals (BaF<Subscript>2</Subscript>)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(LaF<Subscript>3</Subscript>)<Subscript>x</Subscript> activated by Ce<Superscript>3+</Superscript> ions

The electron paramagnetic resonance (EPR) spectra of mixed crystals (BaF₂)_{1?x? y}(LaF₃)_x(CeF₃)_y (y = 0.001 = 0.1%, x = 0–0.02) are investigated in a magnetic field H‖C₄ at a frequency of 9.5 GHz. The angular dependence of the EPR spectrum is measured for the sample with x = 0.02. The lines attributed to Ce³⁺ impurity centers with tetragonal symmetry and g factors (g_‖ = 0.75, g_⊥ = 2.4) close to those measured for the KY₃F₁₀: Ce³⁺ compound are separated in the complex EPR spectrum. The assumption is made that the aforementioned impurity centers are cubooctahedral clusters of the La₆F₃₇ type in which one of the La³⁺ ions is replaced by the Ce³⁺ ion.