Combining high pressure and coherent diffraction: a first feasibility test

We present a first experiment combining high pression and coherent X-ray diffraction. By using a dedicated diamond anvil cell, we show that the degree of coherence of the X-ray beam is preserved when the X-ray beam passes through the diamond cell. This observation opens the possibility of studying the dynamics of slow fluctuations under high pressure.Comment: 3 pages, 2 figures, GHPR 2009 conferenc

Charge and Spin Density Waves observed through their spatial fluctuations by coherent and simultaneous X-ray diffraction

Spatial uctuations of spin density wave (SDW) and charge density wave (CDW) in chromium have been compared by combining coherent and simultaneous X-ray diffraction experiments. Despite their close relationship, spatial fluctuations of the spin and of the charge density waves display a very different behavior: the satellite reflection associated to the charge density displays speckles while the spin one displays an impressive long-range order. This observation is hardly compatible with the commonly accepted magneto-elastic origin of CDW in chromium and is more consistent with a purely electronic scenario where CDW is the second harmonic of SDW. A BCS model taking into account a second order nesting predicts correctly the existence of a CDW and explains why the CDW is more sensitive to punctual defects.Comment: 4 pages, 4 figures; Accepted in Phys. Rev.

The SrTiO3_3 displacive transition revisited by Coherent X-ray Diffraction

We present a Coherent X-ray Diffraction study of the antiferrodistortive displacive transition of SrTiO$_3$, a prototypical example of a phase transition for which the critical fluctuations exhibit two length scales and two time scales. From the microbeam x-ray coherent diffraction patterns, we show that the broad (short-length scale) and the narrow (long-length scale) components can be spatially disentangled, due to 100 $\mu$m-scale spatial variations of the latter. Moreover, both components exhibit a speckle pattern, which is static on a $\sim$10 mn time-scale. This gives evidence that the narrow component corresponds to static ordered domains. We interpret the speckles in the broad component as due to a very slow dynamical process, corresponding to the well-known \emph{central} peak seen in inelastic neutron scattering.Comment: 4 pages, 3 figures, accepted in PR

The essential role of surface pinning in the dynamics of charge density waves submitted to external dc fields

A Charge Density Wave (CDW) submitted to an electric field displays a strong shear deformation because of pinning at the lateral surfaces of the sample. This CDW transverse pinning was recently observed but has received little attention from a theoretical point of view until now despite important consequences on electrical conductivity properties. Here, we provide a description of this phenomenon by considering a CDW submitted to an external dc electric field and constrained by boundary conditions including both longitudinal pinning due to electrical contacts and transverse surface pinning. A simple formula for the CDW phase is obtained in 3D by using the Green function and image charges method. In addition, an analytical expression of the threshold field dependence on both length and sample cross section is obtained by considering the phase slip process. We show that the experimental data are well reproduced with this model and that bulk pinning can be neglected. This study shows that the dynamical properties of CDW systems could be mainly driven by boundary effects, despite the comparatively huge sample volumes.Comment: 7 pages of main text, 7 pages of appendices 15 figure

Origin of the anomaly in diffuse scattering from disordered Pt-V alloys

An explanation of the anomalous concentration dependence of diffuse scattering from the Pt-V alloy system (splitting of the (100) short-range order intensity peak with increasing Pt content) is proposed. The effect is attributed to the competition between the interaction and self-energy curvatures. A similar temperature behaviour is predicted.Comment: 5 pages, 5 EPS figures, RevTeX; minor editorial corrections, text as publishe

Using virtual reality and 3D industrial numerical models for immersive interactive checklists

At the different stages of the PLM, companies develop numerous checklist-based procedures involving prototype inspection and testing. Besides, techniques from CAD, 3D imaging, animation and virtual reality now form a mature set of tools for industrial applications. The work presented in this article develops a unique framework for immersive checklist-based project reviews that applies to all steps of the PLM. It combines immersive navigation in the checklist, virtual experiments when needed and multimedia update of the checklist. It provides a generic tool, independent of the considered checklist, relies on the integration of various VR tools and concepts, in a modular way, and uses an original gesture recognition. Feasibility experiments are presented, validating the benefits of the approach

Carbon Nanotubes Synthesized in Channels of Alpo4-5 Single Crystals : First X-Ray Scattering Investigations

Following the synthesis of aligned single-wall carbon nanotubes in the channels of AlPO4-5 zeolite single crystals, we present the first X-ray diffraction and diffuse scattering results. They can be analysed in terms of a partial filling of the zeolite channels by nanotubes with diameter around 4A. The possible selection of only one type of nanotube during the synthesis, due to the constraints imposed by the zeolite host, is discussed.Comment: to appear in Solid State Com