Improved calculation of the structure functions of the nucleon in the O(4, 2)-infinite multiplet model

A new investigation of the inelastic electon scattering from proton in the O(4, 2) models is presented. The resultant explicit structure functions in the limit satisfy scaling, F₁(ξ) ≠ 0 (σ_T ≠ 0), the Drell-Yan relation F₂(ξ) ～ (1?ξ)³ and, approximately, the Callan-Gross relation F₂(ξ) ≈ 2ξF₁(ξ).     

Magnetic field investigation of the acoustic impedance resonance near 2Δ(T) in 3He-A

The acoustic impedance resonance near 2Δ(T) in ³He-A has been studied in magnetic fields up to H = 0.72 T with H?q?. It now appears that the resonance reported by Meisel et al. is independent of ?, q? orientation and satisfies ω(T) = a_ξΔ(T), where Δ(T) is the maximum in the weak coupling axial state gap and a_ξ = 1.8.     

Hopping conduction in disordered carbon nanotubes

We report electrical transport measurements on individual disordered multiwalled carbon nanotubes, grown catalytically in a nanoporous anodic aluminum oxide template. In both as-grown and annealed types of nanotubes, the low-field conductance shows an exp[−(T₀/T)^1/2] dependence on temperature T, suggesting that hopping conduction is the dominant transport mechanism, albeit with different disorder-related coefficients T₀. The electric field dependence of low-temperature conductance behaves as exp[−(ξ₀/ξ)^1/2] at high electric field ξ at sufficiently low T. Finally, both annealed and unannealed nanotubes exhibit weak positive magnetoresistance at . Comparison with theory indicates that our data are best explained by Coulomb-gap variable-range hopping conduction and permits the extraction of disorder-dependent localization length and dielectric constant.     

The physical properties of borocarbide superconductor Y1−xSmxNi2B2C (x≦0.25) and Y1−xSmxPd5B3C0.4 (x≦0.4)

We have investigated the magnetic and transport properties of borocarbide superconductors YNi₂B₂C and YPd₅B₃C_0.4 with Yttrium partially substituted by Samarium. The upper critical fields H_C2 are determined by the scaling analysis of the thermal fluctuation magnetoconductivity. Around the transition region, the thermal fluctuation magnetoconductivity can be scaled by a universal function for all applied magnetic fields. The formula H_C2(T)=H_C2(0)[1−(T/T_C)^3/2]^3/2 of a narrow-band pairing mechanism gives an excellent fit to the value of upper critical field H_C2(0)=7.6 T in the Y_0.8Sm_0.2Pd₅B₃C_0.4 compound. The superconducting coherence length ξ is determined to be 6.58 nm, the Ginzburg-Landau parameter κ is 29 and the penetration depth λ is 191 nm.     

Hyperfine magnetic interactions of 57Fe nuclei in NaFeAs arsenide

The results of the Mössbauer effect studies of layered NaFeAs arsenide in a wide temperature range are presented. The measurements at T > T _N demonstrate that the main part (～90%) of iron atoms are in the low-spin state Fe²⁺. The other atoms can be attributed to the impurity NaFe₂As₂ phase or to the extended defects in NaFeAs. The structural phase transition (at T _S ≈ 55 K) does not produce any effect on hyperfine parameters (δ, Δ) of iron atoms. At T < T _N, the spectra exhibit the existence of a certain distribution of the hyperfine magnetic field (H _Fe) at ⁵⁷Fe nuclei, indicating the inhomogeneity of the magnetic environment around iron cations. The analysis of the temperature behavior of the distribution function p(H _Fe) allows us to determine the temperature of the magnetic phase transition (T _N = 46 ± 2 K). It has been found that the magnetic ordering in the iron sublattice has a two-dimensional type. The analysis of the H _Fe(T) dependence in the framework of the Bean-Rodbell model reveals a first-order magnetic phase transition accompanied by a drastic change in the electron contributions to the main component (V _ZZ ) and the asymmetry parameter (η) of the tensor describing the electric field gradient at ⁵⁷Fe nuclei.     

Courants critiques d'alliages supraconducteurs a concentration modulee spatialement II. — Effet de la temperature

The peak effect observed in the variation of the critical current as a function of the magnetic field H of periodically inhomogeneous films is observed only below a characteristic temperature T¹ given approximately by $\text{2ξ(T}{}^1\text{,}\text{C}\text{) = 2a}$ where 2a is the period of the modulation and C? the mean concentration. We describe the variation of the field values at peak J_c(H) as a function of temperature.     

Thermodynamic Study of Formamidinium Lead Iodide (CH5N2PbI3) from 5 to 357 K

In the present study, the molar heat capacity of solid formamidinium lead iodide (CH₅N₂PbI₃) was measured over the temperature range from 5 to 357 K using a precise automated adiabatic calorimeter. In the above temperature interval, three distinct phase transitions were found in ranges from 49 to 56 K, from 110 to 178 K, and from 264 to 277 K. The standard thermodynamic functions of the studied perovskite, namely the heat capacity C°_p(T), enthalpy [H⁰(T) − H⁰(0)], entropy S⁰(T), and [G°(T) − H°(0)]/T, were calculated for the temperature range from 0 to 345 K based on the experimental data. Herein, the results are discussed and compared with those available in the literature as measured by nonclassical methods.     

Antiferromagnetic Resonance in GdB<Subscript>6</Subscript>

The electron spin resonance has been measured for the first time both in the paramagnetic phase of the metallic GdB₆ antiferromagnet (T_N = 15.5K) and in the antiferromagnetic state (T < T_N). In the paramagnetic phase below T* ~ 70 K, the material is found to exhibit a pronounced increase in the resonance linewidth and a shift in the g-factor, which is proportional to the linewidth Δg(T) ~ ΔH(T). Such behavior is not characteristic of antiferromagnetic metals and seems to be due to the effects related to displacements of Gd³⁺ ions from the centrosymmetric positions in the boron cage. The transition to the antiferromagnetic phase is accompanied by an abrupt change in the position of resonance (from μ₀H₀ ≈ 1.9 T to μ₀H₀ ≈ 3.9 T at ν = 60 GHz), after which a smooth evolution of the spectrum occurs, resulting eventually in the formation of the spectrum consisting of four resonance lines. The magnetic field dependence of the frequency of the resonant modes ω₀(H₀) obtained in the range of 28–69 GHz is well interpreted within the model of ESR in an antiferromagnet with the easy anisotropy axis ω/γ = (H ₀ ² +2H_AH_E)^1/2, where H_E is the exchange field and H_A is the anisotropy field. This provides an estimate for the anisotropy field, H_A ≈ 800 Oe. This value can result from the dipole?dipole interaction related to the mutual displacement of Gd³⁺ ions, which occurs at the antiferromagnetic transition.     

Magnetic properties of tetragonal uranium compounds I. the U2N2Z-ternaries

In the present work we report the magnetic behaviour of the tetragonal ternaries of the U₂N₂Z-type (Z=Sb, Bi and Te). Magnetic susceptibility measurements performed in a wide temperature range (4.2–1000 K) have shown, that they are ferromagnetically ordered with Curie temperatures 166, 154 and 71 K for U₂N₂Sb, U₂N₂Bi and U₂N₂Te, respectively. For all the investigated compounds the κ^-1_M(T) function in the temperature range above T_C can be expressed as (A/T + B)^-1 - λ.Magnetization measurements were carried out up to magnetic field strengths of 140 kOe in the temperature range from 4.2 to the respective T_C. It follows from these measurements that σ(T)_H and σ(H)_T for U₂N₂Sb and U₂ N₂Bi are typical as for normal ferromagnets. On the other hand, U₂N₂Te exhibits, unexpectedly, two distinct maxima on the σ(T) curves up to fields of 4.5 kOe; one at 45 K and the other one at 71 K. Previous neutron diffraction studies of this compound have shown that the magnetic moments of uranium atoms at 4.2 K are titled by about 20° from the basal plane.The results obtained are interpreted in terms of the crystal-field interaction of the 5f² electrons of the U⁴ ion. In consequence a γ_5t doublet is expected to be the ground-state crystal field level in the U₂N₂Z-type as well as in many other ternary uranium tetragonal compounds. However, in the case U₂N₂Te, the singlet-singlet-doublet “band” as a ground system is postulated.     

Magnetic properties of the compounds N(CH3)4MnIIMIII(CN)6 ·8 H2O(MIII = Mn,Fe)

In the isostructural cyanobridged chain compounds N(CH₃)₄Mn^IIM^III(CN)₆ · 8H₂O high spin Mn(II) ions couple antiferromagnetically to low spin Mn(III) of Fe(III) ions. The Mn^II–Mn^III compound orders ferrimagnetically below T_N = 28.5 ± 1 K. The tetragonal a and b axes are easy ones for the magnetic moments. In the Mn^II–Fe^III compound antiferromagnetic order occurs below T_N = 9.3 K, with spins aligned along the tetragonal c axis. The compound undergoes a meta-magnetic transition from the antiferromagnetic to a ferrimagnetic phase. This occurs at 2 K for a field H_crit ≈ 1.2 T. The temperature dependence of H_crit, which vanishes at T_N, is followed. The tricritical temperature T¹ is ～ 5 K.     

Non-perturbative gravitational corrections in a class of N = 2 string duals

We investigate the non-perturbative equivalence of some heterotic/type II dual pairs with N = 2 supersymmetry. The perturbative heterotic scalar manifolds are respectively SU(1, 1)/U(1) × SO(2,2+N_V)/SO(2) × SO(2+N_V) and SO(4,4+N_H)/SO(4) × SO(4+N_H) for moduli in the vector multiplets and hypermultiplets. The models under consideration correspond, on the type II side, to self-mirror Calabi-Yau threefolds with Hodge numbers h^1,1 = N_V + 3 = h^2,1 = N_H + 3, which are K3 fibrations. We consider three classes of dual pairs, with N_V = N_H = 8, 4 and 2. The models with h^1,1 = 7 and 5 provide new constructions, while the h^1,1 = 11, already studied in the literature, is reconsidered here. Perturbative R²-like corrections are computed on the heterotic side by using a universal operator whose amplitude has no singularities in the (T, U) space, and can therefore be compared with the type II side result. We point out several properties connecting K3 fibrations and spontaneous breaking of the N = 4 supersymmetry to N = 2. As a consequence of the reduced S- and T- duality symmetries, the instanton numbers in these three classes are restricted to integers, which are multiples of 2, 2 and 4, for N_V = 8, 4 and 2, respectively.     

Scaling of magnetoresistance of carbon nanomaterials in Mott-type hopping conductivity region

A method for analyzing data on Mott hopping conduction in a magnetic field, ρ ～ exp[(T ₀/T)^α], based on scaling relation ln[ρ(H)/ρ(0)] = (T ₀/T)^α F(H/T) for the spin-polarized contribution to the magnetore-sistance is proposed. This general approach is tested for a carbon nanomaterial synthesized from single-wall carbon nanotubes under high pressure (up to 7 GPa). The experiments confirmed the theoretical predictions over the temperature range 1.8–12.0 K in a magnetic field of up to 70 kOe and made it possible to correctly determine all parameters of the localized states involved in the model. The experimental data obtained for carbon nanomaterials synthesized from single-wall carbon nanotubes and a mixture of C_2N fullerenes indicate the possible renormalization of the magnetic moment of electrons involved in hopping transport.     

Small Values of the Maximum for the Integral of Fractional Brownian Motion

We consider the integral of fractional Brownian motion (IFBM) and its functionals ξ _T on the intervals (0,T) and (?T,T) of the following types: the maximum M _T , the position of the maximum, the occupation time above zero etc. We show how the asymptotics of P(ξ _T <1)=p _T ,T→∞, is related to the Hausdorff dimension of Lagrangian regular points for the inviscid Burgers equation with FBM initial velocity. We produce computational evidence in favor of a power asymptotics for p _T . The data do not reject the hypothesis that the exponent θ of the power law is related to the similarity parameter H of fractional Brownian motion as follows: θ=?(1?H) for the interval (?T,T) and θ=?H(1?H) for (0,T). The point 0 is special in that IFBM and its derivative both vanish there.     

Thermodynamic study of compounds of the Nd-Ba-Cu-O system

Standard enthalpies of formation for solid solutions of composition Nd_{1 + x} Ba_{2 ? x} Cu₃O _y (x = 0–0.8, y = 6.65–7.24) from oxides were determined by solution calorimetry. The heat capacity of NdBa₂Cu₃O_6.87 phase was measured in the range 5–320 K by low-temperature adiabatic calorimetry. The absolute entropy S ^o(T), the difference of enthalpies H ^o(T)-H ^o(0 K), and the reduced Gibbs energy Φ^o(T) = S ^o(T)–[H ^o(T)–H ^o(0)]/T were calculated on the basis of smoothed dependence C _p (T) in the 0–320 K range. An assessment was made for the heat capacities and the absolute entropies of solid solutions Nd_1+x Ba_2?x Cu₃O _y . The obtained set of thermodynamic parameters can be used for the calculation of phase equilibria in the Nd-Ba-Cu-O system.     

Enhancement of the upper critical field of MgB2 by carbon-doping

We have measured the temperature dependence of the upper critical field, H_c2(T), of carbon-doped MgB₂. H_c2(T) does not follow the well-known Werthamer-Helfand-Hohenberg (WHH) result for a one-gap dirty superconductor but can be described well by the result of a recent theoretical calculation for a two-gap dirty superconductor. H_c2(0) of the carbon-doped material is determined to be between 29 and 38 T, substantially higher than that of pure MgB₂ (15-23 T).     

Scaling behavior of the Hall coefficient of Si:P at the metal-insulator transition

Measurements of the Hall coefficient R _H (T, B) of Si:P with P concentration N between 3.54 and 7.0·10¹⁸ cm^?3 are reported for the temperature range 0.04 K ≤ T ≤ 4K and in magnetic fields up to 7 T. Even far above the metal-insulator transition (MIT), a sign change of the temperature coefficient similar to the behavior of the conductivity σ(T) in moderate fields is not observed in R _H (T). Field and temperature dependence of R _H both increase as the MIT (at the critical concentration N _c = 3.52 · 10¹⁸ cm^?3) is approached. A careful extrapolation to T → 0 and B → 0 indicates that R _H ^?1 scales to zero as R _H ^?1 ～| N ? N _c ^μH with μ _H = (0.44 ± 0.04) in agreement with previous results.     

Nuclear magnetic resonance studies of CePd2In and LaPd2In at low temperatures

We report on In nuclear magnetic resonance (NMR) and nuclear quadrupolar resonance (NQR) measurements on the new heavy-electron compound CePdZIn over a wide temperature range, from 45 mK up to 30 K. CePd₂In undergoes an antiferromagnetic (AF) phase transition at T _N = 1.23 K involving small localised Ce moments of 0.11 μ_B. In zero field, the spin-lattice relaxation rate T ₁ ^?1 (T) shows remarkable changes in its temperature dependence. Above 3 K, T ₁ ^?1 is constant and 850 sec^?1. Between T _N and 2T _N, (T ₁ T)^?1 = 330 (Ksec)^?1, but rapidly decreases below T _N. A Korringatype relaxation, characteristic for simple metals at low temperatures, with (T ₂ T)^?1 = 17(Ksec)¹ is resumed below 0.6 K. This value is an order of magnitude larger than (T ₁ T)^?1 for LaPd₂In and therefore is associated with low-energy excitations of the itinerant charge carriers with 4f symmetry. The T ₁ ^?1 data at various non-zero magnetic fields fall on a single curve when plotted as a function of (T/H) if H exceeds 3.5 T. Thus the AF ordering, the 4f moment fluctuations and the Kondo screening are drastically suppressed by the application of fields H of the order of 3.5 T.     

NMR study on the quasi one-dimensional quantum spin magnet with ladder structure

The two-legged spin ladder Cu(CO₃)_0.5(ClO₄)(H₂O)_0.5(NH₃)_2.5 consists of a rung formed by two Cu(II)’s and of a spacing molecule CO\(_{3}^{2-}\) between each two rungs. The non-centrosymmetric shape of CO\(_{3}^{2-}\) molecule brings a slight bond alternation along the leg, and hence the system can be considered as an alternating spin chain, which is confirmed so far by the temperature dependence of magnetic susceptibility. In order to investigate its spin state at low temperatures, we have performed experiments of ¹H-NMR, magnetization and specific heat under wide range of magnetic field, and have found the critical diverging of longitudinal relaxation rate 1/T ₁, the spectral broadening and the lambda-type anomaly in specific heat at T _N? 3.4 K, indicating the existence of long range magnetic order. In paramagnetic state well above T _N, 1/T ₁ showed a power-law temperature dependence, suggesting the realization of Tomonaga Luttinger liquid state.     

Upper critical fields of Nb3Ge thin film superconductors

The upper critical field H_c2(T) of the highest T_c(～23K) Nb₃Ge superconducting films has been found to be ≈370kG at 4.2K. Measurements on lower T_c films show very broad transitions reflecting nonuniformity. The H_c2(T) characteristics are consistent with other Nb₃X type II superconductors.