41 research outputs found
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
The SrTiO displacive transition revisited by Coherent X-ray Diffraction
We present a Coherent X-ray Diffraction study of the antiferrodistortive
displacive transition of SrTiO, 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 m-scale spatial
variations of the latter. Moreover, both components exhibit a speckle pattern,
which is static on a 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
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
Theory of temperature dependence of the Fermi surface-induced splitting of the alloy diffuse-scattering intensity peak
The explanation is presented for the temperature dependence of the fourfold
intensity peak splitting found recently in diffuse scattering from the
disordered Cu3Au alloy. The wavevector and temperature dependence of the
self-energy is identified as the origin of the observed behaviour. Two
approaches for the calculation of the self-energy, the high-temperature
expansion and the alpha-expansion, are proposed. Applied to the Cu3Au alloy,
both methods predict the increase of the splitting with temperature, in
agreement with the experimental results.Comment: 4 pages, 3 EPS figures, RevTeX, submitted to J. Phys. Condens. Matter
(Letter to the Editor
Charge-Density-Waves Tuned by Crystal Symmetry
The electronic orders appearing in condensed matter systems are originating
from the precise arrangement of atoms constituting the crystal as well as their
nature. This teneous relationship can lead to highly different phases in
condensed matter, and drive electronic phase transitions. Here, we show that a
very slight deformation of the crystal structure of TbTe can have a
dramatic influence on the electronic order that is stabilized. In particular,
we show that the Charge Density Wave (CDW) developping along the axis
in the pristine state, switches to an orientation along when the
naturally orthorhombic system is turned into a tetragonal system. This is
achieved by performing true biaxial mechanical deformation of a TbTe sample
from 250K to 375K, and by measuring both structural and electronic parameters
with x-ray diffraction and transport measurements. We show that this switching
transition is driven by the tetragonality parameter , and that the
transition occurs for , with a coexistence region for . The CDW transition temperature is found to have a linear
dependence with , with no saturation in the deformed states investigated
here, while the gap saturates out of the coexistence region. The linear
dependence of is accounted for within a tight-binding model. Our results
question the relationship between the gap and in RTe systems. More
generally, our method of applying true biaxial deformation at cryogenic
temperatures can be applied to many systems displaying electronic phase
transitions, and opens a new route towards the study of coexisting or competing
electronic orders in condensed matter