Magnetization fluctuation analysis and superconducting parameters of , Sm, Gd, Dy, Ho, Yb) superconductor

In this work we report the analysis of magnetization experimental data of the , Sm, Gd, Dy, Ho, Yb) superconducting system. The data are analyzed in terms of thermal fluctuations on the magnetization excess ΔM(T) for different values of temperature in each one of the samples. We describe a procedure for extracting the penetration depth and the coherence length parameters from the magnetization, as a function of the applied magnetic field. This procedure was performed for polycrystalline samples of La_0.5RE_0.5BaCaCu₃O_7-δ by using the theory of Bulaevskii, Ledvij and Kogan, which analyzes the vortex fluctuation in superconducting materials within the Lawrence–Doniach framework. These data allowed to determine the characteristic temperature value T^* (73, 58, 48, 57, 56, 71 K, for RE=Y, Sm, Gd, Dy, Ho, Yb, respectively) in the magnetization curves for several magnetic fields. We calculated the data of magnetization excess from the curves of magnetization as a function of logarithm of applied field. We notice that the values for these superconducting parameters are in agreement with the reports for high temperature superconductors. The obtained value of superconducting volumetric fraction is compared with that obtained through the measure of the Meissner effect.     

Three equations of state for solids considering thermal effect

 The Einstein model to consider thermal effect in universal equations of state (UEOS) is modified. It is proposed that the zero-point vibration term should be deleted in a thermal UEOS, and the parameters cannot be directly taken as experimental data at a reference temperature, V_R, B_R, and , but their values at absolute zero temperature, V₀, B₀, and . An approach is proposed to solve V₀, B₀, and from V_R, B_R, and . The approaches are applied to three typical universal EOSs, including the Baonza, mGLJ and Morse EOSs. The numerical results show that the solved values of parameters are almost identical for different EOSs. And the thermo-physical properties predicted through different EOSs are almost identical at zero- and low-pressure conditions, once the same approach and input experimental data are used to solve the parameters. It is concluded that the prediction of thermo-physical properties at zero- and low-pressure conditions cannot be taken as the criteria to judge the applicability of a universal EOS.     

Photoproduction of and of high mass in ultra-peripheral Au + Au collisions at

We present the first measurement of photoproduction of J/ψ and of two-photon production of high-mass e⁺e⁻ pairs in electromagnetic (or ultra-peripheral) nucleus–nucleus interactions, using Au + Au data at . The events are tagged with forward neutrons emitted following Coulomb excitation of one or both Au nuclei. The event sample consists of 28 events with m_e⁺e⁻>2 GeV/c² with zero like-sign background. The measured cross sections at midrapidity of and for m_e⁺e⁻[2.0,2.8] GeV/c² have been compared and found to be consistent with models for photoproduction of J/ψ and QED based calculations of two-photon production of e⁺e⁻ pairs.     

Symmetry-adapted tight-binding calculations of the totally symmetric A1 phonons of single-walled carbon nanotubes and their resonant Raman intensity

The atomistic calculations of the physical properties of perfect single-walled carbon nanotubes based on the use of the translational symmetry of the nanotubes face increasing computational difficulties for most of the presently synthesized nanotubes with up to a few thousand atoms in the unit cell. This difficulty can be circumvented by use of the helical symmetry of the nanotubes and a two-atom unit cell. We present the results of such symmetry-adapted tight-binding calculations of the totally symmetric A₁ phonons (the RBM and the G-band modes) and their resonant Raman intensity for several hundred nanotubes.In particular, we show that (1) the frequencies and the resonant Raman intensity of the RBM and the G-band modes show diameter and chirality dependence and family patterns, (2) the strong electron– phonon interactions in metallic nanotubes lead to Kohn anomalies at the zone center, (3) the G-band consists of a subband due to phonons of semiconducting tubes centered at 1593 cm⁻¹, a subband of phonons at 1570 cm⁻¹, and a subband of phonons of metallic tubes at 1540 cm⁻¹. The latter prediction confirms previous theoretical results but disagrees with the commonly adopted assignment of the G-band features.     

Structural and electronic behavior of Sr2GdRuO6 complex perovskite

We report experimental and theoretical study of crystallographic lattice and electronic structure of Sr₂GdRuO₆ complex perovskite, which is used as precursor in the fabrication process of superconducting ruthenocuprate RuSr₂GdCu₂O₈. Samples were produced by the standard solid state reaction. Rietveld refinement of experimental X-ray diffraction patterns shows that material crystallizes in a monoclinic structure, which belongs to the P2₁/n (#14) space group, with lattice parameters , , , and tilt angle β=90.258. Calculations of electronic structure were performed by the density functional theory. The exchange and correlation potentials were included through the LDA+U approximation. Density of states (DOS) study was carried out considering the two spin polarizations. Results show Gd are majority responsible for the magnetic character in this material, but Ru contribution is also relevant because d-orbital is closer to Fermi level. Theoretical results evidence that Sr₂GdRuO₆ material behaves as a magnetic semiconductor, with 20μ_B effective magnetic moment.     

Magnetic and structural behavior of double perovskite

We report synthesis and characterization of new Sr₂ZrMnO₆ manganite-like material. Samples were produced by the solid state reaction method with sinterization temperatures up to 1400 °C. X-ray diffraction experiments reveal that structure belongs to the perovskite system, space group . Lattice parameter was obtained by means of Rietveld-type refinement, through the GSAS code. Magnetic properties were studied by using an MPMS Quantum Design SQUID. From measurements of magnetization as a function of temperature, we determine the occurrence of a paramagnetic–antiferromagnetic transition with Néel temperature 50 K. Curie–Weiss fitting permitted to obtain the magnetic characteristic parameters. At temperature regimes below the Néel temperature, strong evidences of frustration and an irreversibility temperature between zero field cooling (ZFC) and field cooling (FC) measurements were observed. Curves of magnetization as a function of applied field were performed at . Results show a hysteretic feature for Sr₂ZrMnO₆ magnetic material. This response is attributed to formation of magnetic clusters as a consequence of cationic (magnetic and no magnetic) disorder along the double perovskite structure.     

Structural, optical and thermal investigations on Dy doped NaF–Li2O–B2O3 glasses

Structural, optical and thermal properties of Dy³⁺ doped lithium fluoroborate glasses have been studied for various concentrations of Dy³⁺ from 0.5 to 5 wt%. The XRD studies confirm the amorphous nature of the glasses while the FTIR spectra reveal the presence of BO₃ and BO₄ local structural units. The UV–VIS–NIR absorption studies were carried out to calculate the bonding parameters ( and δ), to identify the ionic/covalent nature of the glasses. The JO parameters, experimental and theoretical oscillator strengths were also determined and reported. The luminescence spectra have been studied to determine the radiative transition probability (A), stimulated emission cross section () and the experimental and calculated branching ratios (β_R) for the excited levels that include ⁴F_9/2→⁶H_11/2, ⁶H_13/2, and ⁶H_15/2 transitions. The variation of optical properties with varying concentrations of dysprosium oxide content in the glasses are reported and discussed. The thermal behavior of Dy³⁺ doped lithium fluoroborate glasses have been reported by recording DSC thermograms.     

Effects of Co doping on antiferromagnetic structure in

We performed the elastic neutron scattering experiments on the mixed compounds CeRh_1-xCo_xIn₅, and found that doping Co into CeRhIn₅ dramatically changes the antiferromagnetic (AF) structure. The incommensurate AF state with the propagation vector of observed in pure CeRhIn₅ is suppressed with increasing x, and new AF states with an incommensurate and a commensurate modulations simultaneously develop near the AF quantum critical point: x_c0.8. These results suggest that the AF correlations with the q_c and q₁ modulations enhanced in the intermediate Co concentrations may play a crucial role in the evolution of the superconductivity observed above x0.4.     

Polarized neutron reflectometer SUIREN at JRR-3

Recent status of the neutron reflectometer SUIREN is presented. Since its startup in 2006, SUIREN has been the only neutron reflectometer in Japan for magnetic samples with high magnetic field sample environment, and used for investigations of magnetic films, solid-liquid interfaces and other solid thin films. SUIREN provides monochromatic neutron beam of 3.93 Å for vertically placed sample surface. Polarized beam is also available together with a 1 T electromagnet for sample. Beam intensity at the sample position in the unpolarized mode is for beam collimation of Δθ=0.08. Reflectivity can be explored down to 10^-6.     

Effect of In-content on the optical properties of a-Se films

The optical transmission spectra of amorphous (a-) Se_1−xIn_x films, with x = 0.0, 0.05, 0.18 and 0.35, that prepared by thermal evaporation from their corresponding bulk ingots, are recorded over the spectral region of 500–2500 nm. A simple straight forward procedure proposed by Swanepeol has been applied to determine the two components of the complex refractive index (). The dispersion of is examined in terms of the Wemple and DiDomenico model and is discussed in terms of In-content. An estimation of various optical parameters such as, the optical energy gap (E_g = 1.96–1.33 eV), single oscillator energy (E_o = 3.95–3.16 eV), oscillator dispersion energy (E_d = 22.6–31.6 eV), lattice oscillator strength (E_l = 0.38–0.61 eV) and wavelength at zero material dispersion (λ_c = 2.0569–2.0879 μm) have been given and discussed in relation to the coordination number, hydrostatic density and formed chemical bonds that are introduced in the network of a-Se with the introduction of up to 35 at.% In.     

Influence of spin on the activation energies at

The activation energy Δ of the fractional quantum Hall state at constant filling factor and also at and has been measured as a function of the perpendicular magnetic field B while modulating the electron density via a top gate. At small magnetic fields we observe a linear increase of Δ with the magnetic field. The slope of Δ vs. B allows us to directly extract the composite fermion g-factor.     

Polarized neutron scattering studies of the kagomé lattice antiferromagnet

We report polarized neutron scattering studies of spin-wave excitations and spin fluctuations in the lattice antiferromagnet KFe₃(OH)₆(SO₄)₂ (jarosite). Inelastic polarized neutron scattering measurements at 10 K on a single crystal sample reveal two spin gaps, associated with in-plane and out-of-plane excitations. The polarization analysis of quasi-elastic scattering at 67 K shows in-plane spin fluctuations with XY symmetry, consistent with the disappearance of the in-plane gap above the Néel temperature . Our results suggest that jarosite is a promising candidate for studying the 2D XY universality class in magnetic systems.     

Tunneling conductance in a gapped graphene-based superconducting structure: Case of massive Dirac electrons

The tunneling conductance in a NG/SG graphene junction in which the graphene was grown on a SiC substrate is simulated. The carriers in the normal graphene (NG) and the superconducting graphene (SG) are treated as massive relativistic particles. It is assumed that the Fermi energy in the NG and SG are E_FN400 meV and E_FS400 meV+U, respectively. Here U is the electrostatic potential from the superconducting gate electrode. It is seen that the Klein tunneling disappears in the case where a gap exist in the energy spectrum. As U→∞, the zero bias normalized conductance becomes persistent at a minimal value of G/G₀1.2. The normalized conductance G/G₀ is found to depend linearly on U with constant slope of , where is the size of the gap Δ opening up in the energy spectrum of the graphene grown on the SiC substrate. It is found that G/G₀2+αU for potentials in the range −270 meV<U<0 meV and G=0 for potentials U<−270 meV. As α→∞, the conductance for eV=Δ (V is the bias voltage placed across the NG/SG junction) can be approximated by a unit step function G(eV=Δ,U)/G₀2Θ(U). This last behavior indicates that a NG/SG junction made with gapped graphene could be used as a nano switch having excellent characteristics.     

The nature of the rectilinear diameter singularity

The rigorous explanation for the term |t|^2β in the rectilinear diameter equation is given (t=(T_c−T)/T_c, β is the critical exponent for the asymptotic form of the equation of state). The optimal order parameter, for which the branches of binodal are symmetric, is constructed within the canonical formalism. It is shown that the ratio of the amplitudes for the diameter singularity of the order parameter before |t|^1−α and |t|^2β, where α determines the behavior of the heat capacity and β is the critical exponent of the order parameter, takes the universal character modulo non-universal factor which depends on the thermodynamic class of the corresponding states. The analysis of entropy for argon and water leads to β=0.33 and the corresponding amplitude ratio .     

The polarised valence quark distribution from semi-inclusive DIS

The semi-inclusive difference asymmetry A^h+−h− for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002–2004 using a 160 GeV polarised muon beam scattered off a large polarised ⁶LiD target in the kinematic range 0.006<x<0.7 and 1<Q²<100 (GeV/c)². In leading order QCD (LO) the deuteron asymmetry A^h+−h− measures the valence quark polarisation and provides an evaluation of the first moment of Δu_v+Δd_v which is found to be equal to 0.40±0.07(stat.)±0.06(syst.) over the measured range of x at Q²=10 (GeV/c)². When combined with the first moment of previously measured on the same data, this result favours a non-symmetric polarisation of light quarks at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario .     

Vortex penetration depth of κ-(ET)2Cu[N(CN)2]Br

The magnetic field dependence of the in-plane penetration depth λ_|(H) for single crystal κ-(ET)₂Cu[N(CN)₂]Br has been measured at 3, 9.6, and 36 MHz. Over a limited range, λ_| scales with a characteristic field that coincides with a shoulder in the λ_| vs. H curves. Above that field, λ_| increases sharply toward a second inflection point at that coincides with is close to the irreversibility line measured by magnetization. For fields larger than the penetration depth diverges, suggesting that the vortex lattice has melted. The field dependence at one frequency agrees qualitatively with a model of pinned vortices at low fields giving way to flux flow at higher fields. However, the observed frequency dependence deviates significantly from the predictions of this model, suggesting that collective effects play a major role. Our technique also yields a new measurement for the interplane penetration depth λ_⊥ ∼ 300 μm, implying an anisotropy .     

The observation of hot bands in the 288 nm system of the FeCl2 radical

The 288 nm band system of FeCl₂ has been recorded with a sample produced in a warmed, free-jet expansion at moderately high resolution (with a linewidth of 0.28 cm⁻¹). Under these conditions, several hot bands are observed involving excitation of the symmetric and anti-symmetric stretching vibrations. The wavenumbers determined as a result for FeCl₂ in its ground ⁵Δ_g,4 state are and . No hot, sequence bands in the bending vibration were observed. The most likely explanation is that the wavenumber for ν₂ is essentially the same in both the electronic states involved (88 cm⁻¹). Additional strong hot bands are observed that are unrelated to the previously assigned electronic transitions; they appear to emanate from a low-lying electronic state of FeCl₂.     

New observation of the , 1Δg, and 2Πg states and molecular constants with all Li2, Li2, and LiLi data

This paper reports our new observation of the , 1³Δ_g (v = 2–4), and 2³Π_g (v = 2–8) states of ⁶Li⁷Li by continuous wave perturbation facilitated optical–optical double resonance spectroscopy. Combining our new experimental term values of ⁶Li⁷Li with the available experimental data of ⁶Li₂ and ⁷Li₂, molecular constants and potential energy curves by Rydberg–Klein–Rees and direct-potential-fit techniques have been determined. Born-Oppenheimer breakdown parameters of the Li₂ 1³Δ_g and 2³Π_g states are calculated.