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Neutron scattering from high-quality YBa_2Cu_3O_(6.33) (YBCO6.33) single crystals with a T_c of 8.4 K shows no evidence of a coexistence of superconductivity with long-range antiferromagnetic order at this very low, near-critical ...
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Neutron scattering from high-quality YBa_2Cu_3O_(6.33) (YBCO6.33) single crystals with a T_c of 8.4 K shows no evidence of a coexistence of superconductivity with long-range antiferromagnetic order at this very low, near-critical doping of p ～ 0.055. However, we find short-range three-dimensional spin correlations that develop at temperatures much higher than T_c. Their intensity increases smoothly on cooling and shows no anomaly that might signify a Neel transition. The system remains subcritical with spins correlated over only one and a half unit cells normal to the planes. At low energies, the short-range spin response is static on the microvolt scale. The excitations out of this ground state give rise to an overdamped spectrum with a relaxation rate of 3 meV. The transition to the superconducting state below T_c has no effect on the spin correlations. The elastic interplanar spin response extends over a length that grows weakly but fails to diverge as doping is moved towards the superconducting critical point. Any antiferromagnetic critical point likely lies outside the superconducting dome. The observations suggest that conversion from Neel long-range order to a spin-glass texture is a prerequisite to formation of paired superconducting charges. We show that while p_c = 0.052 is a critical doping for superconducting pairing, it is not for spin order.
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Background: Resolution Elastic Neutron Scattering (RENS) method involves performing elastic scattering intensity scans as a function of the instrumental energy resolution and as a function of temperature.
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The present work aims to characterize the dynamical behavior of proteins immersed in bio-preserving liquids and glasses. For this purpose, the protein dUTPase was chosen, while the selected solvents were glycerol, a triol, and som...
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The present work aims to characterize the dynamical behavior of proteins immersed in bio-preserving liquids and glasses. For this purpose, the protein dUTPase was chosen, while the selected solvents were glycerol, a triol, and some homologous disaccharides, i.e., trehalose, maltose, and sucrose, which are known to be very effective bio-preserving agents. The results highlight that the disaccharides show a slowing down effect on the water dynamics, which is stronger for trehalose than in the case of the other disaccharides. Furthermore, a characterization of the medium which hosts the protein is performed by using an operative definition of fragility based on the mean square displacement extracted by elastic incoherent neutron scattering, which is directly connected to Angell’s kinetic fragility based on the viscosity. Finally, a study of the dynamics of the protein sequestered within the solvents is performed. The result shows that the protein dynamics is coupled with that of the surrounding matrix.
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We present comprehensive investigations on a pyrochlore antiferromagnet Na_3Co(CO_3)_2Cl. Performed dc magnetization indicates a broad maximum at around 4 K. The field dependence of the peak temperature of this maximum follows the...
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We present comprehensive investigations on a pyrochlore antiferromagnet Na_3Co(CO_3)_2Cl. Performed dc magnetization indicates a broad maximum at around 4 K. The field dependence of the peak temperature of this maximum follows the de Almeida-Thouless line, suggesting a spin-glass-like phase transition. The ac susceptibility measurements determine the glassy transition temperature to be 4.5 K and reveal a frequency-independent peak at 17 K. The temperature dependence of the specific heat shows a sharp peak at 1.5 K and a broad hump at around 5 K, which are attributed to a long-range magnetic phase transition and a spin-glass-like freezing process, respectively. The average crystallographic structure of Na_3Co(CO_3)_2Cl has been determined using neutron-powder diffraction. No obvious site disorder has been detected within the experimental resolution. The diffuse neutron scattering with polarization analysis indicates short-range spin correlations characterized by dominating antiferromagnetic coupling between nearest neighbors and weak ferromagnetic coupling between next-nearest neighbors. The long-range magnetic order below 1.5 K is evidenced by the magnetic reflections observed at 50 mK and can be well explained with an all-in-all-out spin configuration. Inelastic neutron scattering of Na_3Co(CO_3)_2Cl exhibits collective magnetic excitations at 3.5 K, suggesting that the spin-glass-like transition temperature T_g = 4.5 K does not correspond to a complete spin-glass freezing as expected in canonical spin glasses. The peak observed in magnetic susceptibility at 17 K is attributed to the onset of an intermediate partially ordered phase transition, qualitatively consistent with the theoretical predictions for pyrochlore antiferromagnets with weak ferromagnetic next-nearest-neighbor interactions.
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We have measured neutron-diffraction patterns in a single-crystal sample of the pyrochlore compound Er_2Ti_2O_7 in the antiferromagnetic phase (T=0.3 K), as a function of the magnetic field, up to 6 T, applied along the [110] dire...
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We have measured neutron-diffraction patterns in a single-crystal sample of the pyrochlore compound Er_2Ti_2O_7 in the antiferromagnetic phase (T=0.3 K), as a function of the magnetic field, up to 6 T, applied along the [110] direction. We determine all the characteristics of the magnetic structure throughout the critical point at H_c=1 T. As a main result, all Er moments align along the field at H_c and their values reach a minimum. Using a four-sublattice self-consistent calculation, we show that the evolution of the magnetic structure and the value of the critical field are rather well reproduced using the same anisotropic exchange tensor as that accounting for the local paramagnetic susceptibility. In contrast, an isotropic exchange tensor does not yield the correct moment variations through the critical point. The model also accounts semiquanti-tatively for other experimental data obtained in previous works, such as the field dependence of the heat capacity, energy of the dispersionless inelastic modes and transition temperature.
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Quasielastic neutron scattering measurements are combined with molecular dynamics simulations to extract the self-diffusion coefficient of hydrogen in the metal organic frameworks MIL-47(V) and MIL-53(Cr). We find that the diffusi...
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Quasielastic neutron scattering measurements are combined with molecular dynamics simulations to extract the self-diffusion coefficient of hydrogen in the metal organic frameworks MIL-47(V) and MIL-53(Cr). We find that the diffusivity of hydrogen at low loading is about 2 orders of magnitude higher than in zeolites. Such a high mobility has never been experimentally observed before in any nanoporous materials, although it was predicted in carbon nanotubes. Either 1D or 3D diffusion mechanisms are elucidated depending on the chemical features of the MIL framework.
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We report the formulation of the number of elastic scatterings required to slow down a neutron. By establishing its analytical expression, we show that this number displays a discontinuity and an oscillatory transient that progres...
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We report the formulation of the number of elastic scatterings required to slow down a neutron. By establishing its analytical expression, we show that this number displays a discontinuity and an oscillatory transient that progressively dampens when the neutron energy decreases. This result does not apply to neutrons with energies lower than a few eV, as we restrict our study to scatterings on free stationary nuclei.
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We introduce the use of a higher-order reflection, Si(333), of the silicon analyzer crystals at a backscattering spectrometer to implement analysis of the relaxation dynamics in the samples. This is achieved by monitoring the temp...
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We introduce the use of a higher-order reflection, Si(333), of the silicon analyzer crystals at a backscattering spectrometer to implement analysis of the relaxation dynamics in the samples. This is achieved by monitoring the temperature dependence of the neutron scattering intensity perceived as elastic when measured using Si(111), Si(311), and Si(333) reflections. As a test case, we use a sample with well-characterized, but complex, relaxation pattern, where the non-Lorentzian relaxation function is known to exhibit a set of parameters specific to each temperature point and scattering momentum transfer (Q) value. Even for this very general relaxation pattern, characterized by no constrains on the relaxation function parameters, we successfully map the relaxation times measured using the present approach onto those previously obtained from the full analysis of the quasielastic neutron scattering signal. Analysis of the Q-specific activation energies becomes possible for the Q values accessible simultaneously through Si(111), Si(311), and Si(333) reflections (in the present case, 0.9 angstrom(-1) < Q < 1.9 angstrom(-1)). While the dedicated neutron spectrometers for this type of analysis are yet to be constructed, we show that the present-day backscattering spectrometers can be employed, under certain conditions, to analyze temperature dependence of the relaxation time in the samples not amenable to traditional full analysis of the quasielastic neutron scattering signal.
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We review the current state of the field of neutron scattering as applied to studies of mineral behaviour. Neutron scattering is a particularly versatile tool because it is able to measure both structure (diffraction) and dynamics...
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We review the current state of the field of neutron scattering as applied to studies of mineral behaviour. Neutron scattering is a particularly versatile tool because it is able to measure both structure (diffraction) and dynamics (spectroscopy) of materials at an atomic level, and because it is able to measure both coherent and incoherent scattering processes. As a result, there is a wide range of phenomena that can be studied using neutron scattering. The versatility of the tool is shown to arise within a general theoretical framework. Applications of neutron scattering in the Earth and Mineral Sciences are described.
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Small momentum transfer elastic pion-proton cross-section at high energies is calculated assuming the proton is composed of two constituents, a quark and a diquark. We find that it is possible to fit very precisely the data when (...
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Small momentum transfer elastic pion-proton cross-section at high energies is calculated assuming the proton is composed of two constituents, a quark and a diquark. We find that it is possible to fit very precisely the data when (i) the pion acts as a single entity (no constituent quark structure) and (ii) the diquark is rather large, comparable to the size of the proton.
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