The short-range nucleon-nucleon repulsion

The short-range repulsion (0.2–0.4 fm) between nucleons is investigated. The opposing effects of ω-meson exchange and ε-meson (J^p = 0⁺) exchange are investigated, and the relation to Regge behaviour is demonstrated using fixed-s dispersion relations. The energy dependence of the short-range interaction is emphasized, and experimental data on polarization in elastic NN scattering at high energy are used to give the necessary coupling constant.     

Unconventional spin-charge phase separation in a model 2D cuprate

In this work, we address a challenging problem of a competition of charge and spin orders for high-T _c cuprates within a simplified 2D spin-pseudospin model which takes into account both conventional Heisenberg Cu²⁺?Cu²⁺ antiferromagnetic spin exchange coupling (J) and the on-site (U) and intersite (V) charge correlations in the CuO₂ planes with the on-site Hilbert space reduced to only three effective charge states (nominally Cu^1+;2+;3+). We performed classical Monte Carlo calculations for large square lattices implying the mobile doped charges and focusing on a case of a small intersite repulsion V ? J. The on-site attraction (U < 0) does suppress the antiferromagnetic ordering and gives rise to a checkerboard charge order with the doped charge distributed randomly over a system in the whole temperature range. However, under the on-site repulsion (U > 0) the homogeneous ground state antiferromagnetic solutions of the doped system found in a mean-field approximation are shown to be unstable with respect to a phase separation with the charge and spin subsystems behaving like immiscible quantum liquids. Puzzlingly, with lowering the temperature one can observe two sequential phase transitions: first, an antiferromagnetic ordering in the spin subsystem diluted by randomly distributed charges, then, a charge condensation in the charge droplets. The effects are illustrated by the Monte Carlo calculations of the specific heat and longitudinal magnetic susceptibility.     

Glass composition dependence of Eu ion red fluorescence

Eu³⁺ ion-doped B₂O₃-, SiO₂-, and P₂O₅-based glasses were prepared by the melt-quenching method, and their absorption, fluorescence, and excitation spectra were recorded and assigned. The glass composition dependence of the fluorescence was investigated to obtain the high brightness of the red fluorescence due to the ⁵D₀→⁷F₂ transition of the Eu³⁺ ion. The integrated intensity of the red fluorescence was the strongest at the Eu₂O₃ concentration of 3.5 mol% because the cross-relaxation (CR) processes, (⁵L₆→⁵D_J^′)→(⁷F_J^*←⁷F_J^#) and (⁵D_J→⁵D_J^′)→(⁷F_J^*←⁷F_J^#) (3≧J>J′≧0, 6≧J^*>J^#≧0) between the Eu³⁺ ions were promoted, but the CR processes, (⁵D₀→⁷F_J^′)→∑_m(⁷F_J^*←⁷F_J^″)_m (6≧J′≧0, 6≧J^*>J^″≧0), between the excited Eu³⁺ ion at the ⁵D₀ level and m ions of Eu³⁺ in the ⁷F_J^″ levels were depressed. The former CR processes, (⁵L₆→⁵D_J^′)→(⁷F_J^*←⁷F_J^#) and (⁵D_J→⁵D_J^′)→(⁷F_J^*←⁷F_J^#) were enhanced in the host glasses consisted of the cations with small ionic radius. In this study, a 70B₂O₃-30CaO-3.5Eu₂O₃ glass showed the strongest red fluorescence.     

Line-mixing between rotational Stark components of CH3F self-perturbed and perturbed by helium: Experimental results and IOS analysis

Self- and He-broadening coefficients of microwave transitions of CH₃F have been measured with and without the presence of an external electric field. This provides values for the J, K → J + 1, K (K = 0 − J) transitions for J = 1 and J = 3 as well as for the various J, K, M → J + 1, K, M′ (|M| = 0 − K, |M - M′| = 0, 1) Stark components. The results and those of a previous experimental study for pure CH₃F, which show significant line-mixing effects, are analyzed with a model based on the Infinite Order Sudden approximation. It is shown that the latter leads to very satisfactory modeling of observed values even though no parameter was adjusted since previously and independently determined basic cross-sections are used. The quality of the present predictions is comparable with that obtained previously with a semi-classical approach. Furthermore, it is shown that the previously stated inaccuracy of the IOS model was due to an oversimplified use of this approach.     

The spin-1 Blume–Capel model on the Bethe lattice in ± J distribution with an adjustable parameter between FM and AFM phases

The spin-1 Blume–Capel (BC) model is studied on the Bethe lattice (BL) for the ?±? J distribution with a competing adjustable parameter α which alters the strength of bilinear exchange interaction parameter for the ferromagnetic phase (J?>?0) with respect to antiferromagnetic phase (J?<?0). The J?>?0 and αJ?<?0 values are also distributed throughout the BL with probabilities p and $1?p,$ respectively. The order-parameters are obtained on the BL in terms of exact recursion relations (ERR’s) and their temperature (T) variations are studied to calculate the phase diagrams on the (α, T) planes for given values of p, crystal field (D) and coordination number $q=3$ corresponding to honeycomb lattice. It is found that the model gives both first- and second-order phase transitions and also tricritical points. In addition to the well known ordinary phases and TCP’s, the spin glass phase and two more special points are also observed.     

Observation by ICLAS VeCSEL technique, and rotational analysis, of the ΔvGeH=5 stretching vibrational overtone of H3GeD

The fourth GeH stretching overtone band of monoisotopic H₃⁷⁰GeD at 9877 cm⁻¹ has been recorded by ICLAS VeCSEL technique with a path length equivalent to 26 km. The (500 A₁/E) band has been observed and rotationally analyzed up to J^′=18. The band was shown to be essentially unperturbed except some high J states. The assigned transitions were fitted, with σ(Fit) ca. 6.5 × 10⁻³ cm⁻¹. While eight refined parameters were needed up to J^′_max=14, six quartic centrifugal distortion constants were refined in addition for the larger body of 829 data with J^′_max=18. The (500 A₁/E) parameters of H₃⁷⁰GeD perfectly fulfill the theoretical relations valid at the local mode limit, and they fit into the series for other (n00 A₁/E) levels (n=2, 3, 6, 7, and 8). A transition moment ratio M(A₁):M(E)=0.25 was found to be in best agreement with the observed spectrum, only high J (J^′?13) transitions being evidently sensitive to this ratio.     

Phase diagram of the two-dimensional Ising model with random competing interactions

An Ising model with ferromagnetic nearest-neighbor interactions J₁ (J₁>0) and random next-nearest-neighbor interactions [+J₂ with probability p and −J₂ with probability (1−p); J₂>0] is studied within the framework of an effective-field theory based on the differential-operator technique. The order parameters are calculated, considering finite clusters with n=1,2, and 4 spins, using the standard approximation of neglecting correlations. A phase diagram is obtained in the plane temperature versus p, for the particular case J₁=J₂, showing both superantiferromagnetic (low p) and ferromagnetic (higher values of p) orderings at low temperatures.     

Electrical conduction in a semicrystalline polyethylene terephthalate in high electric field

Measurements of conduction currents were carried out on polyethylene terephthalate semi crystalline PET in an electrical field region varying from 40 to 260 V/μm. Various mechanisms of conduction (Richardson-Schottky, Fowler-Nordheim, Poole-Frenkel, space charge limited current SCLC, Hopping), can cause non-linear characteristics. To highlight the mechanism responsible for conduction in the PET, we used the slope of the experimental curve Log(J)=f(E) in the region 150<E<260 V/μm, to calculate the value of the dielectric permittivity. The characteristic curve Log(J)=f(1/T) shows that the Poole-Frenkel mechanism of conduction is prevalent in the semi crystalline PET. The characteristic J=f(E) for various thicknesses shows that the field threshold increases with the thickness.     

Effect of the surface integral in the torque equation of the electromagnetic angular momentum on the Faraday rotation

A circularly polarized plane wave of infinite transverse extent (δ = ∞) has no spin angular momentum, while a realistic light does carry it. This paradox originates from the presence (δ = ∞) and absence (δ ≈ 0) of the surface integral in the total angular momentum J. The same holds for the torque equation of dJ/dt, so that δ is also connected with the relative Faraday rotation angle Θ_F/θ_F when a radius (a) of a cylindrical medium with optical activity is only a little larger than that (b) of light beam, where Θ_F is the Faraday rotation angle and θ_F is the intrinsic Faraday rotation angle of a medium. It is shown here that it is possible to estimate δ for a realistic light from the drastic variation in Θ_F/θ_F near b/a = 1.     

The pure rotational Raman spectrum of CS2 in the ground and 010 vibrational states

The pure rotational Raman spectra of CS₂ in the 00⁰0 and 01¹0 vibrational states have been observed using a low power HeNe laser (λ = 6328 Å) and a high resolution plane grating spectrograph. The ΔJ = 2 transitions with J = odd in the 01¹0 state are clearly resolved from the ground state transitions thus allowing the determination of some upper state rotational constants. The molecular constants determined in this work are for the 00⁰0 ground state, B_00⁰0 = 0.10912 ± 0.7 × 10⁻⁵ cm⁻¹, (D_J)_00⁰0 = (0.83 ± 0.18) × 10⁻⁸ cm⁻¹ and for the 01¹0 excited state B_01¹0^c = 0.10935 ± 0.00002 cm⁻¹ and (D_J)_01¹0^c = (1.5 ± 0.6) × 10⁻⁸ cm⁻¹.     

Relationship between crystallization process and superconducting properties of YBCO films by TFA–MOD method using starting solution with various compositions

We have investigated the influence of partial pressure of water vapor [P(H₂O)] in the crystallization process on the superconducting properties of YBa₂Cu₃O_7−y (YBCO) films fabricated by a trifluoroacetate–metal organic deposition (TFA–MOD) method. The starting solution with different compositions of Y: Ba:Cu = 1.0:2.0:3.0 and 1.0:1.5:2.0 were studied. The critical current density (J_c) values of YBCO films fabricated from Y:Ba:Cu = 1.0:2.0:3.0 starting solution significantly increase (1.71 → 2.55 MA/cm²) with increasing P(H₂O) from 12.3 to 47.4 kPa. In the YBCO films fabricated from Y:Ba:Cu = 1.0:1.5:2.0 starting solution, high J_c values of over 2.5 MA/cm² were recognized in a wide range of P(H₂O) (12.3–47.4 kPa). One of the reason for J_c improvement is the suppression of coarsening of the secondary phases grains such as Y₂Cu₂O₅ and CuO due to increase in growth rate of YBCO layer in the crystallization process. The J_c values of all YBCO films decreased as P(H₂O) increased up to 70.1 kPa. This degradation of J_c values may be caused by difference of crystal growth mechanism in high growth rate.     

Rotational spectra of gauche perfluoro-n-butane, C4F10; perfluoro-iso-butane, (CF3)3CF; and tris(trifluoromethyl)methane, (CF3)3CH

The microwave spectra of the gauche conformer of perfluoro-n-butane, n-C₄F₁₀, of perfluoro-iso-butane, (CF₃)₃CF, and of tris(trifluoromethyl)methane, (CF₃)₃CH, have been observed and assigned. The rotational and centrifugal distortion constants for gauche n-C₄F₁₀ are: A = 1058.11750(7) MHz, B = 617.6832(1) MHz, C = 552.18794(1) MHz, Δ_J = 0.0257(5) kHz, δ_J = 0.0052(3) kHz. A C-C-C-C dihedral angle, ω, of ∼55° has been determined. These values agree well with those obtained from a coupled cluster (CCSD/cc-PVTZ) calculation. The rotational and centrifugal distortion constants for iso-C₄F₁₀ and iso-C₄HF₉ are: B_o = 816.4519(4) MHz, D_J = 0.023(2) kHz, and B_o = 903.6985(25) MHz, D_J = 0.043(4) kHz, respectively. The dipole moment of iso-C₄F₁₀ and iso-C₄HF₉ have been measured and found to be 0.0338(8) and 1.69(9) D, respectively.     

Phase structure of a U(1) lattice gauge theory with dual gauge fields

We introduce a U(1) lattice gauge theory with dual gauge fields and study its phase structure. This system is partly motivated by unconventional superconductors like extended s-wave and d  -wave superconductors in the strongly-correlated electron systems and also studies of the t–J$t\text{–}J$ model in the slave-particle representation. In this theory, the “Cooper-pair” (or RVB spinon-pair) field is put on links of a cubic lattice due to strong on-site repulsion between original electrons in contrast to the ordinary s  -wave pair field on sites. This pair field behaves as a gauge field dual to the U(1) gauge field coupled with the hopping of electrons or quasi-particles of the t–J$t\text{–}J$ model, holons and spinons. By Monte Carlo simulations we study this lattice gauge model and find a first-order phase transition from the normal state to the Higgs (superconducting) phase. Each gauge field works as a Higgs field for the other gauge field. This mechanism requires no scalar fields in contrast to the ordinary Higgs mechanism. An explicit microscopic model is introduced, the low-energy effective theory of which is viewed as a special case of the present model.     

Non-planar spin texture driven dissipation in a ferromagnet-superconductor bilayer

We report the observation of a pronounced dip in the in-plane magnetic field (H_∥) dependence of the critical current density J_c(H) and a peak in resistance R(H) of a NbN-HoNi₅ bilayer at temperatures below the magnetic ordering temperature (T_Curie ≈ 3.5 K) of HoNi₅, which is lower than the onset temperature (≈9 K) of superconductivity in the NbN layer. The extrema in J_c(H) and R(H) appear at fields much below the upper critical field of NbN. We attribute these features to a coupling between localized out-of-plane moments present in the magnetic film and Pearl vortices of the superconducting layer. A spin re-orientation transition of the localized moments by H_∥ breaks this coupling, leading to the observed excess dissipation.     

The magnetic state of diamagnetically diluted antiferromagnetic cobalt and nickel monoxide

The nearest neighbour J₁(x) and the next-neighbour super-exchange J₂(x) interactions are evaluated by using the mean field theory for Mg1−xBxO (B=Co and Ni) systems. The magnetic energy E(x) is obtained. A magnetic phase diagram of the Mg1−xBxO (B=Co and Ni) solid solutions with 0?x?1 is drawn by high-temperature series expansions (HTSE) combined with the Padé approximants method (PA). The critical exponents associated with the magnetic susceptibility (γ) and with the correlation length (ν) are deduced in order phase.     

Pressure-induced H2 opacity in the 5-μm region

The H₂ opacity arising from the pure-rotational hexadecapole-induced U₀(J) transitions occurring during H₂H₂ and H₂He collisions, and from the hexadecapole-induced U₀(J) + S₀(J′) and the quadrupole-induced S₀(J) + S₀(J′) transitions in H₂He collisions, has been calculated. The U₀(J) and S₀(J) + S₀(J′) contributions from H₂H₂ collisions are important H₂ opacities in the frequency range from 700–3000 cm^?1 for temperatures appropriate to the outer planets. It is concluded that this opacity is needed in addition to the opacity from the extrapolation of the 0-0 and 1-0 H₂H₂ collisionally induced bands to interpret the spectrum at 5 μm for the outer planets.     

Device and performance parameters of Cu(In,Ga)(Se,S)2-based solar cells with varying i-ZnO layer thickness

In pursuit of low-cost and highly efficient thin film solar cells, Cu(In,Ga)(Se,S)₂/CdS/i-ZnO/ZnO:Al (CIGSS) solar cells were fabricated using a two-step process. The thickness of i-ZnO layer was varied from 0 to 454 nm. The current density-voltage (J-V) characteristics of the devices were measured, and the device and performance parameters of the solar cells were obtained from the J-V curves to analyze the effect of varying i-ZnO layer thickness. The device parameters were determined using a parameter extraction method that utilized particle swarm optimization. The method is a curve-fitting routine that employed the two-diode model. The J-V curves of the solar cells were fitted with the model and the parameters were determined. Results show that as the thickness of i-ZnO was increased, the average efficiency and the fill factor (FF) of the solar cells increase. Device parameters reveal that although the series resistance increased with thicker i-ZnO layer, the solar cells absorbed more photons resulting in higher short-circuit current density (J_sc) and, consequently, higher photo-generated current density (J_L). For solar cells with 303-454 nm-thick i-ZnO layer, the best devices achieved efficiency between 15.24% and 15.73% and the fill factor varied between 0.65 and 0.67.     

The effects of C substitution and disorder on the field dependent critical current density in MgB2 with nano-SiC additions

In this work, nano sized SiC powders were mixed with Mg and B and reacted by either a one-step insitu or two-step method resulted in different level of C substitution. X-ray diffraction shows the presence of Mg₂Si signifying that the reaction between SiC and Mg occurred leading to the release of C in samples reacted in one-step method. Moreover, the much reduced value of a-axis indicates C substitution took place. Resistivity measurements showed higher intragrain scattering owing to a higher density of defects and/or impurities. These samples also show higher H_irr and H_c2 at 20 K in comparison to samples with mainly unreacted SiC (hence lower C substitution). More importantly, their J_c’s are more insensitive to high magnetic field (>4 T) at 6 K. However, at 20 K the effect of C content on J_c(H) is less pronounced. Finally, the order of magnitude of J_c(H) at both 6 K and 20 K is rather dominated by pinning.     

Spin-orbit coupling of the NaK 3Π and 3Π states: Determination of the coupling constant and observation of quantum interference effects

We have studied the mutually perturbing 3³Π_Ω=0(v = 32, J = 19) ∼ 3¹Π_Ω=1(v = 6, J = 19) levels of NaK that are coupled together by the spin-orbit interaction. We note that this coupling is nominally forbidden by the ΔΩ = 0 selection rule for spin-orbit perturbations. However 3³Π levels labeled by different values of Ω are mixed by rotational coupling; i.e. the 3³Π_Ω levels are best described by a coupling scheme intermediate between Hund’s cases (a) and (b). Thus the 3¹Π_Ω=1 level couples to the 3³Π_Ω=0 level via the small admixture of 3³Π_Ω=1 character in the latter. The 3³Π_Ω=0(v = 32, J = 19) ∼ 3¹Π_Ω=1(v = 6, J = 19) f symmetry pair is of particular interest since it appears to be very close to a 50-50 mixture of triplet and singlet character, and the splitting between these levels provides a direct measure of the 3³Π ∼ 3¹Π spin-orbit coupling constant. On the other hand, excitation spectra of the 3³Π_Ω=0(v = 32, J = 19) ∼ 3¹Π_Ω=1(v = 6, J = 19) e symmetry pair through the mixed “window” levels 1(b)³Π_Ω=0(v = 17, J = 18, 20) ∼ 2(A)¹Σ⁺(v = 18, J = 18, 20) display dramatic quantum interference effects associated with “singlet” and “triplet” excitation channels. Almost complete cancellation for populating one or the other of the two upper states is observed for excitation from the predominantly triplet members of the window level pairs.     

New types of short-range orientational ordering in ortho-para hydrogen monolayers

Orientational ordering in monolayers of solid hydrogen is discussed in view of recent experimental findings in NMR studies of (ortho)_c-(para)_1−c-hydrogen mixtures on boron nitride substrate reported for ortho-H₂ concentrations 0.35≤c≤0.92 and temperatures 0.14≤T≤1.80 K. Analysis of the temperature-concentration behavior for the observed NMR frequency splitting is given on the basis of a two-dimension (J=1)_c-(J=0)_1−c-rotor model for which the fundamental parameters, quadrupolar coupling constant Γ₀=0.50±0.03 K and the crystal-field amplitude V₀=0.70±0.10 K, are derived from experiment. The two distinct para-rotational (PR) short-range ordered structures driven by positive and negative crystalline fields are described in terms of the local alignment and orientation of the polar principal axis. It is shown that they are rather different from the ferromagnetic-type ordering suggested earlier by Harris and Berlinsky as a unique PR structure. The common quadrupolar glass and a new hindered rotor phases found below the 2D site percolation threshold c_p=0.72 are also discussed.