Mn<Subscript>4</Subscript>Si<Subscript>7</Subscript>-Si〈Mn〉-Mn<Subscript>4</Subscript>Si<Subscript>7</Subscript> and Mn<Subscript>4</Subscript>Si<Subscript>7</Subscript>-Si〈Mn〉-<Emphasis Type="Italic">M</Emphasis> photodiodes

The current-voltage characteristics of Mn₄Si₇-Si〈Mn〉-Mn₄Si₇ and Mn₄Si₇-Si〈Mn〉-M photodiodes are studied experimentally. The current passage mechanism under illumination with hν ≥ E _g is considered. The role of a contact to Mn₄Si₇ in the provision of high photosensitivity under illumination of the base by light with hν ≥ 1.14 eV at low temperatures, 77–220 K, is analyzed. From electrical measurements, electron microscopic data for the Mn₄Si₇-Si〈Mn〉 interface, and photocurrent-voltage characteristics, a band diagram under the conditions of photocurrent passage is constructed. The high low-temperature photosensitivity of the diodes (I _ph/I _d ≥ 10⁹) is explained by the impact-ionization-induced modulation of the base conductivity and injection amplification of holes in the transition layer.     

Orientation dependence of electrical properties of 0.96Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-0.04BaTiO<Subscript>3</Subscript> lead-free piezoelectric single crystal

In this paper, a single crystal of 0.96Na_0.5Bi_0.5TiO₃-0.04BaTiO₃ with dimensions of Φ 30×10 mm was grown by the top-seeded-solution growth method. X-ray powder diffraction results show that the as-grown crystal possesses the rhombohedral perovskite-type structure. The dielectric, piezoelectric and electrical conductivity properties were systematically investigated with 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples. The room-temperature dielectric constants for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples are found to be 650, 740 and 400 at 1 kHz. The (T _m, ε _m) values of the dielectric temperature spectra are almost independent of the crystal orientations; they are (306°C, 3718), (305°C, 3613) and (307°C, 3600) at 1 kHz for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal. The optimum poling conditions were obtained by investigating the piezoelectric constants d ₃₃ as a function of poling temperature and poling electric field. For the 〈001〉 and 〈110〉 crystal samples, the maximum d ₃₃ values of 146 and 117 pC/N are obtained when a poling electric field of 3.5 kV/mm and a poling temperature of 80°C were applied during the poling process. The as-grown 0.96Na_0.5Bi_0.5TiO₃-0.04BaTiO₃ crystal possesses a relatively large dc electrical conductivity, especially at higher temperature, having a value of 1.98×10⁻¹¹ Ω⁻¹⋅m⁻¹ and 3.95×10⁻⁹ Ω⁻¹⋅m⁻¹ at 25°C and 150°C for the 〈001〉 oriented crystal sample.     

Anisotropy of the upper critical field and specific heat in V3Si — a superconductor with cubic symmetry

The specific heat of a V₃Si single crystal (T _c=17 K, H _c2=20 T) in magnetic fields up to 8 T isinvestigated experimentally for three orientations of the field relative to the crystallographic directions — H∥〈001〉, H∥〈110〉, and H∥〈111〉. Both the upper critical magnetic field and the specific heat of the mixed state are observed to depend on the orientation of the magnetic field relative to the crystallographic directions (anisotropy): The critical field reaches its maximum value and the specific heat its minimum value in a field along the 〈001〉 direction. The anisotropy scale in both phenomena increases as the magnetic field and reaches 3% in a 6 T field. The interrelationship of the upper critical field anisotropy and the specific-heat anisotropy in type-II superconductors is studied. It is shown that the anisotropy of the specific heat in the mixed state in weak fields can serve as a criterion for nontrivial pairing. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 1, 26–29 (10 January 1999)     

Mean square number fluctuation for a fermion source and its dependence on neutrino mass for the universal cosmic neutrino background

Using the general formulation for obtaining chemical potentialμ of an ideal Fermi gas of particles at temperature T, with particle rest mass m₀ and average density 〈N〉/V, the dependence of the mean square number fluctuation 〈ΔN ²〉/V on the particle mass m₀ has been calculated explicitly. The numerical calculations are exact in all cases whether rest mass energym ₀c² is very large (non-relativistic case), very small (ultra-relativistic case) or of the same order as the thermal energy k_BT. Application of our results to the detection of the universal very low energy cosmic neutrino background (CNB), from any of the three species of neutrinos, shows that it is possible to estimate the neutrino mass of these species if from approximate experimental measurements of their momentum distribution one can extract, someday, not only the density 〈N _v〉/V but also the mean square fluctuation 〈Δ _v ² 〉/V. If at the present epoch, the universe is expanding much faster than thermalization rate for CNB, it is shown that our analysis leads to a scaled neutrino massm _v instead of the actual massm _0v .     

Theory of melting,vacancy model

A theory of melting based on vacancy model is formulated. The polymer solution theory is used for derivation of the melting equation for a two-species model of melting solid. Under simplifying assumptions the analysis leads to a simple correlation betweenT _m and 〈v〉, the average energy of interaction between the vibrating atoms. Pseudopotential method is used for calculating 〈v〉 for the alkali metals lithium, sodium, potassium and rubidium at temperatureT _m. The calculated values ofT _m〈v〉 are in accord with those expected from our model. Application to the high pressure melting curves of solids is also discussed.     

Lattice mechanical properties of noble and transition metals

A model pseudopotential depending on an effective core radius but otherwise parameter free is used to study the interatomic interactions, phonon dispersion curves (inq and r-space analysis), phonon density of states, mode Grüneisen parameters, dynamical elastic constants (C ₁₁,C ₁₂ andC ₄₄), bulk modulus (B), shear modulus (C′), deviation from Cauchy relation (C ₁₂–C ₄₄), Poisson’s ratio (σ), Young’s modulus (Y), behavior of phonon frequencies in the elastic limit independent of the direction (Y ₁), limiting value in the [110] direction (Y ₂), degree of elastic anisotropy (A), maximum frequencyω _max, mean frequency 〈ω〉, 〈ω ²〉^1/2=(〈ω〉/〈ω ⁻¹〉)^1/2, fundamental frequency 〈ω ²〉, and propagation velocities of the elastic constants in Cu, Ag, Au, Ni, Pd, and Pt. The contribution of s-like electrons is calculated in the second-order perturbation theory for the model potential while that of d-like electrons is taken into account by introducing repulsive short-range Born-Mayer like term. Very recently proposed screening function due to Sarkar et al. has been used to obtain the screened form factor. The theoretical results are compared with experimental findings wherever possible. A good agreement between theoretical investigations and experimental findings has proved the ability of our model potential for predicting a large number of physical properties of transition metals.     

Statistical mechanics of braided Markov chains: I. Analytic methods and numerical simulations

We investigate numerically and analytically the statistics of Markov chains on so-called braid (B _n ) and locally free (ℒℱ _n ) groups. Namely, we compute the mean length 〈μ〉 and the variance 〈μ²〉−〈μ〉² of the shortest word which remains after applying of all group relations to the randomly generatedN-letter word (Markov chain). We express the conjecture (numerically justified) that the mean value 〈μ〉 for the random walk on the groupB _n (n≫1) coincides with high accuracy with the same value for the random walk on the “locally free group weth errors” if the number of errors is of order of 20%.     

Bell Inequalities as Constraints on Unmeasurable Correlations

The interpretation of the violation of Bell-Clauser-Horne inequalities is revisited, in relation with the notion of extension of QM predictions to unmeasurable correlations. Such extensions are compatible with QM predictions in many cases, in particular for observables with compatibility relations described by tree graphs. This implies classical representability of any set of correlations 〈A _i 〉, 〈B〉, 〈A _i B〉, and the equivalence of the Bell-Clauser-Horne inequalities to a non void intersection between the ranges of values for the unmeasurable correlation 〈A ₁ A ₂〉 associated to different choices for B. The same analysis applies to the Hardy model and to the “perfect correlations” discussed by Greenberger, Horne, Shimony and Zeilinger. In all the cases, the dependence of an unmeasurable correlation on a set of variables allowing for a classical representation is the only basis for arguments about violations of locality and causality.     

The total yields of K *(892)+, Σ+(1385), and Σ0 in neutrino-induced reactions at ? E v? ≈ 10 GeV

Using the data obtained with the SKAT bubble chamber, the total yields of K*(892)⁺, Σ⁺(1385), and Σ⁰ are estimated for the first time in neutrino-induced reactions at moderate energy 〈E _v〉 = 10.4 GeV. It is shown that the recently observed enhancement of the K ⁰ and Λ yields in vA interactions as compared to vN interactions is contributed only slightly by the K*(892)⁺ and Σ⁺(1385) production. The contribution of resonances to the K ⁰ and Λ yields is found to be in qualitative agreement with higher energy (〈E _v〉 ≳ 40 GeV) data. It is shown that the energy dependence of the K*(892)⁺ mean multiplicity in vN interactions is approximately linear in the range of 〈E _v〉 ≈ 10−60 GeV, while that for Σ⁰ in vA interactions (A = 20−21) is approximately logarithmic in the range of 〈E _v〉 ≈ = 10−150 GeV. The text was submitted by the authors in English.     

Long SiC nanowires synthesized from off-gases of the polycarbosilane-derived SiC preparation

In this communication, we report on the attempt to make full use of the off-gases from polycarbosilane-derived SiC preparation, and we successfully synthesized long SiC nanowires in large areas with Fe(NO₃)₃ as catalyst. The nanowires have diameters of about 80–300 nm and lengths of millimeters, and they are identified as single crystals β-SiC along the 〈111〉 direction. The VLS mechanism was employed to interpret the nanowire growth.     

Investigation of low-temperature quantum diffusion in α-iron byμ + SR experiments on a single-crystal sphereSR experiments on a single-crystal sphere

The longitudinalμ ⁺-spin relaxation rate has been measured on a high-purity spherical α-iron single crystal at temperaturesT down to 20 mK and in applied magnetic fieldsB _appl parallel to 〈111〉 up to 3 T. Only above 1 K can the data be satisfactorily described by one rate constantГ. At 1 T≤B _appl≤2 T and 50 mK≤T≤300 mK, oscillations (“wiggles”) were in addition superimposed on the longitudinal relaxation. A qualitative understanding of the measurements may be achieved in terms of the increasing influence of internal stresses onμ ⁺ diffusion as the temperature is lowered.     

Realization of a heavily doped and fully compensated semiconductor state in a crystalline semiconductor with a deep impurity band

We use the data on the pressure (up to P=1.5 GPa) and field (up to H=17 kOe) dependence of the Hall coefficient and the resistivity at 77.6 and 300 K in p-CdSnAs₂〈Cu〉 to calculate the effective kinetic characteristics of the charge carriers, the density and mobility of the conduction electrons and the holes of the deep acceptor and valence bands, in an interval of excess-acceptor densities N _ext ranging from 10¹⁰–10¹⁷ cm⁻³. We establish that in a heavily doped semiconductor with a deep impurity band at the tail of the density of states of the intrinsic band, with unequal donor and acceptor densities, a a heavily doped and fully compensated semiconductor state is realized under hydrostatic compression. The threshold value of the pressure that initiates the transition into such a state, P _c, depends on the extent to which the impurity band is populated. In p-CdSnAs₂〈Cu〉 at N _ext=N _A, where N _A is the density of deep acceptors, and T⩽77.6 K the value of P _c amounts to 10⁻⁴ GPa. As the population of the deep acceptor band grows, P _c increases and in the limit becomes infinite. We discuss the special features of the electrophysical properties of p-CdSnAs₂〈Cu〉 arising from the absence of an energy gap between the states of the conduction band and those of the deep acceptor band. Zh. éksp. Teor. Fiz. 111, 562–574 (February 1997)     

Change of superdislocation splitting with strain in single crystals of the Ni3Fe ordered alloy

The method of transmission electron microscopy is used to study the dislocation structure in single crystals of the Ni ₃ Fe ordered alloy for different degrees of strain. The [1812], [011], [111] and [001] single crystal orientations are examined. The superdislocation splitting (r) is measured for different degrees of strain, distributions of r are constructed, and their average values 〈r〉 are estimated. The 〈r〉-ε curves are constructed. With the use of the experimental r values, the effective energy of antiphase boundaries ζ* is estimated. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 51–56, January, 2006.     

Model-independent analysis of the neutral-current interaction in the inclusive neutrino reactions

On the basis of some general assumptions on the deep inelastic structure functions, such as scaling and chiral symmetry we determine the values of {(H _V ³)²+(H _A ³)²}+η{(H _V ⁰)²+(H _A ⁰)²} andH _V ³ H _A ³+ηH _V ⁰ H _A ⁰ whereH _V ^3,0 andH _A ^3,0 are the four coupling constants characterizing the hadronic neutral current andη is the ratio of the isoscalar to isovector structure functions. General expressions are given for the kinematical averages 〈v〉 and 〈Q ²〉 for the neutral-current reactions in terms of the coupling constants. This analysis does not depend on the validity of the quark-parton model.     

New phase transition in an easy-axis “triangular” antiferromagnet

The NMR of ⁵⁵Mn in the quasi-one-dimensional noncollinear anti-ferromagnet CsMnI₃ is investigated at T=1.3 K in magnetic fields up to ∼80 kOe and angles between the field and C ₆ axis ϕ≈ 0.5° and ϕ=7°. A new reorientational magnetic phase transition is observed in a field H _c1≈39.0 kOe. The magnetic structure for H>H _c1 is determined. The average Mn²⁺ spins of the magnetic sublattices in the new phase are determined from an analysis of the NMR spectrum to be 〈 S _C 〉=1.63 and 〈S _D 〉=1.72. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 12, 988–993 (25 June 1998)     

Using the full Raman depolarisation in the determination of the order parameters in liquid crystal systems

The depolarisation ratio for the Raman-active phenyl stretching mode has been measured over the whole of the mesophase range, and the orientational order parameters deduced, in the uniaxial nematic liquid crystal octylcyanobiphenyl (8CB). Linearly polarised light was incident normally on a homogeneously aligned sample and a χ² minimisation routine performed on the 360^° depolarisation ratio profile. The order parameters 〈P ₂₀₀〉 and 〈P ₄₀₀〉 , together with the differential polarisability ratio, r , are used as fitting parameters and measured as a function of temperature. Interestingly, we show that the value for r , conventionally measured in the isotropic phase and assumed to remain constant, has a clear temperature dependence, ranging from -0.032±0.008 in the isotropic phase through to -0.245±0.015 at the nematic-to-smectic A phase transition. The measured order parameters 〈P ₂₀₀〉 and 〈P ₄₀₀〉 varied from 0.35- 0.55±0.02 and 0.180- 0.245±0.02 , respectively, across the 8 ^° C wide nematic phase range. The values of both 〈P ₂₀₀〉 and 〈P ₄₀₀〉 are in excellent agreement with theory, but it is noteworthy that 〈P ₄₀₀〉 shows a much better quantitative match than has been reported in previous work. Crucially the temperature dependence of r is shown to be a contributing factor in the low 〈P ₄₀₀〉 values that have been conventionally reported from Raman scattering measurements. The potential for fitting the entire angular depolarisation ratio distribution in liquid crystalline systems that are described by more order parameters, specifically biaxial materials, is discussed.     

Evidence of an intermediate phase in ternary Ge<Subscript>7</Subscript>Se<Subscript>93-x</Subscript>Sb<Subscript>x</Subscript> glasses

The compositional dependence of thermal properties, such as glass transition temperature (T_g), non-reversing enthalpy change (ΔH_NR) and the specific heat capacity change (ΔC_p) of melt quenched Ge₇Se_93-xSb_x (21 ≤ x ≤ 31) glasses, has been studied using alternating differential scanning calorimetry (ADSC) which is analogous to modulated differential scanning calorimetry (MDSC). The glass transition temperature, T_g, which is a measure of global connectivity of the glass, has been found to increase with the addition of Sb. In addition, a change in slope has been observed in the composition dependence of T_g at an average coordination 〈r〉 = 2.40. The experimentally observed compositional variation of glass transition temperature, has been compared with the theoretical predictions from the stochastic agglomeration theory (SAT) and has been found to be consistent. Further, a narrow thermally reversing window is seen in the compositional variation of the relaxation enthalpy (ΔH_NR), which is centered around 〈r〉 = 2.40. The change in specific heat capacity (ΔC_p) at T_g is also found to exhibit a distinct minima at 〈r〉 = 2.40, suggesting that the structural rearrangements for the liquid in the glass transition region are minimized around 〈r〉 = 2.4.     

Wave mechanics of two hard core quantum particles in A 1-D box

The wave mechanics of two impenetrable hard core particles in a 1-D box is analyzed. Each particle in the box behaves like an independent entity represented by a macro-orbital (a kind of pair waveform). While the expectation value of their interaction, 〈 V _HC (x) 〉, vanishes for every state of two particles, the expectation value of their relative separation, 〈 x 〉, satisfies 〈 x 〉≥λ/2 (or q ≥ π/d, with 2d=L being the size of the box). The particles in their ground state define a close-packed arrangement of their wave packets (with 〈 x 〉= λ/2, phase position separation Δϕ = 2π and momentum |q _o| = π/d) and experience a mutual repulsive force (zero point repulsion) f _o =h ²/2md ³ which also tries to expand the box. While the relative dynamics of two particles in their excited states represents usual collisional motion, the same in their ground state becomes collisionless. These results have great significance in determining a correct microscopic understanding of widely different many-body systems.     

PAC study on111Cd in antiferromagnetic CuO

400 keV¹¹¹In⁺ ions were implanted into CuO powder. After annealing at 570 K, more than 50% of the implants were found on substitutional sites in the monoclinic CuO lattice. PAC-spectra taken below the Néel temperatureT _N≈230 K revealed a broadening of the quadrupole spectrum and additional satellite frequencies caused by combined electric and magnetic hyperfine interaction. Assuming that the orientation of the electric field gradient is given by the point charge model and taking the 〈010〉 direction of the supertransferred fieldB _tr in CuO from neutron diffraction, we find a Larmor frequency of ω_L≈40 MHz corresponding toB _tr≈2.7 T at 60 K. Supported in part by BMFT under contract FK213N54930.     

X-ray dosimetric characteristics of CdIn2S4〈Cu〉 single crystals

The effect of doping CdIn₂S₄ single crystals by copper (3 mol %) on their X-ray dosimetric characteristics is investigated. It is found that the characteristic X-ray conductivity of CdIn₂S₄〈Cu〉 single crystals increases 3–16 times compared with undoped CdIn₂S₄ at effective radiation hardness V _a = 25−50 keV and dose rate E = 0.75−78.05 R/min. Moreover, the persistence of the crystal characteristics completely disappears and the supply voltage of a CdIn₂S₄〈Cu〉 X-ray detector decreases fivefold. The dependence of the steady X-ray-induced current in CdIn₂S₄〈Cu〉 on the X-ray dose is described as ΔI _{E, 0} ∝ E ^α, where 0.6 ≤ α ≤ 1.8.