Laboratoire Léon Brillouin

UMR12 CEA-CNRS, Bât. 563 CEA Saclay

91191 Gif sur Yvette Cedex, France

+33-169085241 llb-sec@cea.fr

BD diffusons les neutrons

Faits marquants scientifiques 2017

11 septembre 2017

Neutron experiments conducted by the Institut Laue-Langevin (ILL) and CNRS researchers, and performed on the neutron time-of-flight spectrometer (IN5@ILL) and 2T triple axis spectrometer at the Laboratoire Léon Brillouin (LLB), provide a direct quantitative measurement of phonon lifetimes in polymeric cage molecules, giving a novel picture of thermal conductivity in complex materials.

This study highlights the importance of neutron techniques in overcoming the challenging task of accessing and therefore successfully measuring phonon lifetimes.

 

06 septembre 2017

Stehane Longeville et Laura-Roxana Stingaciu

Translational diffusion of macromolecules in cell is generally assumed to be anomalous due high macromolecular crowding of the milieu. Red blood cells are a special case of cells filled quasi exclusively (95% of the dry weight of the cell) with an almost spherical protein: hemoglobin. Hemoglobin diffusion has since a long time been recognized as facilitating the rate of oxygen diffusion through a solution. We address in this paper the question on how hemoglobin diffusion in the red blood cells can help the oxygen capture at the cell level and hence to improve oxygen transport. We report a measurement by neutron spin echo spectroscopy of the diffusion of hemoglobin in solutions with increasing protein concentration. We show that hemoglobin diffusion in solution can be described as Brownian motion up to physiological concentration and that hemoglobin diffusion in the red blood cells and in solutions at similar concentration are the same. Finally, using a simple model and the concentration dependence of the diffusion of the protein reported here, we show that hemoglobin concentration observed in human red blood cells (≃≃330 g.L−1) corresponds to an optimum for oxygen transport for individuals under strong activity.

24 août 2017

Crystal-electric-field excitations and spin dynamics in Ce3Co4Sn13 semimetallic chiral-lattice phase
Kazuaki Iwasa, Yuka Otomo, Kazuya Suyama, Keisuke Tomiyasu, Seiko Ohira-Kawamura, Kenji Nakajima, and Jean-Michel Mignot

Inelastic neutron scattering experiments have been conducted to investigate the spin dynamics and crystal-electric-field level scheme of the Ce 4f electrons in Ce3Co4Sn13 . This compound exhibits a large specific heat at low temperatures and anomalous semimetallic transport in the chiral crystallographic phase below 160 K. Distinctly observed magnetic excitations at approximately 6 and 29 meV are asymmetric in spectral shape and are reproduced by two inequivalent crystal-electric-field splitting schemes, which are deduced from the chiral structure. We have also observed the spin dynamics reflecting antiferromagnetic correlations below 1 meV, which is enhanced with an upturn in the electrical resistivity below 15 K and which yields a low-energy density of state relevant to the large specific heat. We discuss the possibility of a three-dimensional Weyl semimetal state, considering the chiral-lattice symmetry, electronic hybridization, and magnetic correlation.

21 décembre 2017

D. Bounoua, R. Saint-Martin, S. Petit, P. Berthet, F. Damay, Y. Sidis, F. Bourdarot, and L. Pinsard-Gaudart, Phys. Rev. B 95, 224429

The low energy magnetic excitations spectra of the pristine and doped quasi-one-dimensional spin chains cuprates SrCuO2 have been investigated by inelastic neutron scattering. The momentum-integrated magnetic dynamical structure factor yields a constant integrated intensity with regard to energy in the pure compound, while it shows a strong decay, at low energies, in the compounds doped with nonmagnetic impurities, namely, SrCu0.99M0.01O2 (with M=Zn or Mg) and Sr0.99La0.01CuO2 (Cu+ carrying S=0 created within the chains). These results evidence the opening of a spin pseudogap in the two-spinon continuum of SrCuO2 upon doping, stemming from disruptions of the spin chains by quantum impurities.

01 juin 2017

La richesse de la structure électronique de certains matériaux, dits "à électrons fortement corrélés", leur confère de nombreuses propriétés de nature intrinsèquement quantique, telles que la supraconductivité, ou encore l'état d'isolant de Mott (localisation des électrons de conduction) ou de liquide de spin (état magnétique frustré) [1]. Plusieurs interactions électroniques sont responsables de ces fortes corrélations : au-delà de la simple interaction électrostatique, attractive avec les noyaux des atomes et répulsive entre électrons, on trouve l'interaction résultant du principe d'exclusion de Pauli, qui interdit l'occupation d'un même état par deux électrons, et l'interaction spin-orbite (interaction relativiste entre la vitesse d'un électron et son spin).

Parmi ces matériaux, les chercheurs du LLB, en collaboration avec le Laboratoire de Physique du Solide d'Orsay, montrent que des composés iridates (anion d'iridium) à structure pérovskite présentent à basse température un nouvel état magnétique [2], généré, selon un modèle similaire à celui proposé pour les supraconducteurs à haut Tc, par des boucles de courant de la taille de la maille cristalline [3]. Les similitudes structurales et de propriétés électroniques entre les deux familles de composés éclairent d'un jour nouveau les différents états des solides à électrons fortement corrélés, aux nombeuses applications (électronique de spin, capteurs magnétiques, supraconducteurs, ...) .

14 mars 2017

Liquide et solide désordonné se distinguent en premier lieu par leur viscosité : l'un coule, l'autre pas. Mais existe-t-il de réelles différences de structure entre ces deux états de la matière et quelle est la nature exacte la transition "vitreuse" qui les sépare ? Si des réponses ont pu être apportées pour des liquides composés d'atomes ou de petites molécules, ces questions se posent aussi pour les polymères fondus, constitués de longues chaines de molécules. Cette question est technologiquement d'importance, puisque la solidification de liquides polymères est au cœur de beaucoup de procédés, tel que le façonnage de la matière plastique.

Une collaboration de spécialistes du domaine, incluant des chercheurs du LLB, montre toute la spécificité du problème de la transition vitreuse pour les polymères, qui font apparaitre une dimension caractéristique supplémentaire : leur longueur de chaine. Si pour les courtes longueurs de chaine, un comportement générique est bien observé à la température de transition vitreuse, des déviations significatives apparaissent pour les longues chaines. Il est alors montré que l'accord peut être rétabli en considérant une propriété dynamique plus macroscopique, telle que la viscosité du polymère.

 

26 octobre 2017

Raphael Dos Santos Morais, Olivier Delalande, Javier Pérez, Liza Mouret, Arnaud Bondon, Anne Martel, Marie-Sousai Appavou, Elisabeth Le Rumeur, Jean-François Hubert, and Sophie Combet

Obtaining structural information on integral or peripheral membrane proteins is currently arduous due to the difficulty of their solubilization, purification, and crystallization (for X-ray crystallography (XRC) application). To overcome this challenge, bicelles are known to be a versatile tool for high-resolution structure determination, especially when using solution and/or solid state nuclear magnetic resonance (NMR) and, to a lesser extent, XRC. For proteins not compatible with these high-resolution methods, small-angle X-ray and neutron scattering (SAXS and SANS, respectively) are powerful alternatives to obtain structural information directly in solution. In particular, the SANS-based approach is a unique technique to obtain low-resolution structures of proteins in interactions with partners by contrast-matching the signal coming from the latter. In the present study, isotropic bicelles are used as a membrane mimic model for SANS-based structural studies of bound peripheral membrane proteins. We emphasize that the SANS signal coming from the deuterated isotropic bicelles can be contrast-matched in 100% D2O-based buffer, allowing us to separately and specifically focus on the signal coming from the protein in interaction with membrane lipids. We applied this method to the DYS-R11–15 protein, a fragment of the central domain of human dystrophin known to interact with lipids, and we were able to recover the signal from the protein alone. This approach gives rise to new perspectives to determine the solution structure of peripheral membrane proteins interacting with lipid membranes and might be extended to integral membrane proteins.

06 septembre 2017

Stehane Longeville et Laura-Roxana Stingaciu

Translational diffusion of macromolecules in cell is generally assumed to be anomalous due high macromolecular crowding of the milieu. Red blood cells are a special case of cells filled quasi exclusively (95% of the dry weight of the cell) with an almost spherical protein: hemoglobin. Hemoglobin diffusion has since a long time been recognized as facilitating the rate of oxygen diffusion through a solution. We address in this paper the question on how hemoglobin diffusion in the red blood cells can help the oxygen capture at the cell level and hence to improve oxygen transport. We report a measurement by neutron spin echo spectroscopy of the diffusion of hemoglobin in solutions with increasing protein concentration. We show that hemoglobin diffusion in solution can be described as Brownian motion up to physiological concentration and that hemoglobin diffusion in the red blood cells and in solutions at similar concentration are the same. Finally, using a simple model and the concentration dependence of the diffusion of the protein reported here, we show that hemoglobin concentration observed in human red blood cells (≃≃330 g.L−1) corresponds to an optimum for oxygen transport for individuals under strong activity.

21 décembre 2017

D. Bounoua, R. Saint-Martin, S. Petit, P. Berthet, F. Damay, Y. Sidis, F. Bourdarot, and L. Pinsard-Gaudart, Phys. Rev. B 95, 224429

The low energy magnetic excitations spectra of the pristine and doped quasi-one-dimensional spin chains cuprates SrCuO2 have been investigated by inelastic neutron scattering. The momentum-integrated magnetic dynamical structure factor yields a constant integrated intensity with regard to energy in the pure compound, while it shows a strong decay, at low energies, in the compounds doped with nonmagnetic impurities, namely, SrCu0.99M0.01O2 (with M=Zn or Mg) and Sr0.99La0.01CuO2 (Cu+ carrying S=0 created within the chains). These results evidence the opening of a spin pseudogap in the two-spinon continuum of SrCuO2 upon doping, stemming from disruptions of the spin chains by quantum impurities.

17 novembre 2017

A. K. Nayak, V. Kumar, T. Ma, P. Werner, E. Pippel, R. Sahoo, F. Damay, U. K. Rößler, C. Felser and S. S. P. Parkin,  Nature 548, 561566.

Magnetic skyrmions are topologically stable, vortex-like objects surrounded by chiral boundaries that separate a region of reversed magnetization from the surrounding magnetized material. They are closely related to nanoscopic chiral magnetic domain walls, which could be used as memory and logic elements for conventional and neuromorphic computing applications that go beyond Moore’s law. Of particular interest is ‘racetrack memory’, which is composed of vertical magnetic nanowires, each accommodating of the order of 100 domain walls, and that shows promise as a solid state, non-volatile memory with exceptional capacity and performance. Its performance is derived from the very high speeds (up to one kilometre per second) at which chiral domain walls can be moved with nanosecond current pulses in synthetic antiferromagnet racetracks. Because skyrmions are essentially composed of a pair of chiral domain walls closed in on themselves, but are, in principle, more stable to perturbations than the component domain walls themselves, they are attractive for use in spintronic applications, notably racetrack memory. Stabilization of skyrmions has generally been achieved in systems with broken inversion symmetry, in which the asymmetric Dzyaloshinskii–Moriya interaction modifies the uniform magnetic state to a swirling state. Depending on the crystal symmetry, two distinct types of skyrmions have been observed experimentally, namely, Bloch and Néel skyrmions. Here we present the experimental manifestation of another type of skyrmion—the magnetic antiskyrmion—in acentric tetragonal Heusler compounds with D2d crystal symmetry. Antiskyrmions are characterized by boundary walls that have alternating Bloch and Néel type as one traces around the boundary. A spiral magnetic ground-state, which propagates in the tetragonal basal plane, is transformed into an antiskyrmion lattice state under magnetic fields applied along the tetragonal axis over a wide range of temperatures. Direct imaging by Lorentz transmission electron microscopy shows field-stabilized antiskyrmion lattices and isolated antiskyrmions from 100 kelvin to well beyond room temperature, and zero-field metastable antiskyrmions at low temperatures. These results enlarge the family of magnetic skyrmions and pave the way to the engineering of complex bespoke designed skyrmionic structures.

31 juillet 2017

Three-legged 2,2′-bipyridine monomer at the air/water interface: monolayer structure and reactions with Ni(II) ions from the subphase,
Wenyang Dai, Lay-Theng Lee, Andri Schütz, Benjamin Zelenay, Zhikun Zheng, Andreas Borgschulte, Max Döbeli, Wasim Abuillan, Oleg V. Konovalov, Motomu Tanaka and A. Dieter Schlüter, Langmuir, 2017, 33 (7),  1646

The behavior of compound 2 [1,3,5-tri(2,2′-bipyridin-5-yl)benzene] with three bipyridine units arranged in a star geometry is investigated in the presence and absence of Ni(ClO4)2. Its properties at the air–water interface as well as after transfer onto a solid substrate are studied by several techniques including Brewster angle microscopy, X-ray reflectivity, neutron reflectivity, X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and atomic force microscopy combined with optical microscopy. It is found that compound 2 within the monolayers formed stays almost vertical at the interface and that at high Ni2+/2 (Ni2+/2 = 4000, 20′000) ratios two of the three bipyridine units of 2 are complexed, resulting in supramolecular sheets that are likely composed of arrays of linear metal–organic complexation polymers.


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