103 research outputs found
Acoustic Nature of the Boson Peak in Vitreous Silica
New temperature dependent inelastic x-ray (IXS) and Raman (RS) scattering
data are compared to each other and with existing inelastic neutron scattering
data in vitreous silica (v-SiO_2), in the 300 - 1775 K region. The IXS data
show collective propagating excitations up to Q=3.5 nm^-1. The temperature
behaviour of the excitations at Q=1.6 nm^-1 matches that of the boson peak
found in INS and RS. This supports the acoustic origin of the excess of
vibrational states giving rise to the boson peak in this glass.Comment: 10 pages and 4 figure
High frequency longitudinal and transverse dynamics in water
High-resolution, inelastic x-ray scattering measurements of the dynamic
structure factor S(Q,\omega) of liquid water have been performed for wave
vectors Q between 4 and 30 nm^-1 in distinctly different thermodynamic
conditions (T= 263 - 420 K ; at, or close to, ambient pressure and at P = 2
kbar). In agreement with previous inelastic x-ray and neutron studies, the
presence of two inelastic contributions (one dispersing with Q and the other
almost non-dispersive) is confirmed. The study of their temperature- and
Q-dependence provides strong support for a dynamics of liquid water controlled
by the structural relaxation process. A viscoelastic analysis of the
Q-dispersing mode, associated with the longitudinal dynamics, reveals that the
sound velocity undergoes the complete transition from the adiabatic sound
velocity (c_0) (viscous limit) to the infinite frequency sound velocity
(c_\infinity) (elastic limit). On decreasing Q, as the transition regime is
approached from the elastic side, we observe a decrease of the intensity of the
second, weakly dispersing feature, which completely disappears when the viscous
regime is reached. These findings unambiguously identify the second excitation
to be a signature of the transverse dynamics with a longitudinal symmetry
component, which becomes visible in the S(Q,\omega) as soon as the purely
viscous regime is left.Comment: 28 pages, 12 figure
Radiative Ke3 decays revisited
Motivated by recent experimental results and ongoing measurements, we review
the chiral perturbation theory prediction for radiative Ke3 decays (neutral
kaons). Special emphasis is given on the stability of the inner
bremsstrahlung-dominated relative branching ratio vs. the Ke3 form factors, and
on the separation of the structure dependent amplitude in differential
distributions over the phase space. For the structure dependent terms, an
assessment of the order p^6 corrections is given. In particular, a full
next-to-leading order calculation of the axial component is performed. The
experimental analysis of the photon energy spectrum is discussed, and other
potentially useful distributions are introduced.Comment: Version published in Eur.Phys.J.C.: 23 pages (LaTeX), 10 figures.
Minor changes in text, typos removed, references updated, Springer style file
use
Aspects of Strangeness -1 Meson-Baryon Scattering
We consider meson-baryon interactions in S-wave with strangeness -1. This is
a sector populated by plenty of resonances interacting in several two-body
coupled channels. We consider a large set of experimental data, where the
recent experiments are remarkably accurate. This requires a sound theoretical
description to account for all the data and we employ Unitary Chiral
Perturbation Theory up to and including O(p^2). The spectroscopy of our
solutions is studied within this approach, discussing the rise from the pole
content of two \Lambda(1405) resonances and of the \Lambda(1670),
\Lambda(1800), \Sigma(1480), \Sigma(1620) and \Sigma(1750). We finally argue
about our preferred fit.Comment: 6 figures, 3 figures, talk given in the IVth International Conference
on Quarks and Nuclear Physics (QNP06), Madrid June 5th and 10th, 2006. One
reference is update
A large-solid-angle X-ray Raman scattering spectrometer at ID20 of the European Synchrotron Radiation Facility
An end-station for X-ray Raman scattering spectroscopy at beamline ID20 of the European Synchrotron Radiation Facility is described. This end-station is dedicated to the study of shallow core electronic excitations using non-resonant inelastic X-ray scattering. The spectrometer has 72 spherically bent analyzer crystals arranged in six modular groups of 12 analyzer crystals each for a combined maximum flexibility and large solid angle of detection. Each of the six analyzer modules houses one pixelated area detector allowing for X-ray Raman scattering based imaging and efficient separation of the desired signal from the sample and spurious scattering from the often used complicated sample environments. This new end-station provides an unprecedented instrument for X-ray Raman scattering, which is a spectroscopic tool of great interest for the study of low-energy X-ray absorption spectra in materials under insitu conditions, such as inoperando batteries and fuel cells, insitu catalytic reactions, and extreme pressure and temperature conditions.Peer reviewe
Low-energy electronic excitations and band-gap renormalization in CuO
Combining nonresonant inelastic x-ray scattering experiments with state-of-the-art ab initio many-body calculations, we investigate the electronic screening mechanisms in strongly correlated CuO in a large range of energy and momentum transfers. The excellent agreement between theory and experiment, including the low-energy charge excitations, allows us to use the calculated dynamical screening as a safe building block for many-body perturbation theory and to elucidate the crucial role played by d-d excitations in renormalizing the band gap of CuO. In this way we can dissect the contributions of different excitations to the electronic self-energy which is illuminating concerning both the general theory and this prototypical material.Combining nonresonant inelastic x-ray scattering experiments with state-of-the-art ab initio many-body calculations, we investigate the electronic screening mechanisms in strongly correlated CuO in a large range of energy and momentum transfers. The excellent agreement between theory and experiment, including the low-energy charge excitations, allows us to use the calculated dynamical screening as a safe building block for many-body perturbation theory and to elucidate the crucial role played by d-d excitations in renormalizing the band gap of CuO. In this way we can dissect the contributions of different excitations to the electronic self-energy which is illuminating concerning both the general theory and this prototypical material.Combining nonresonant inelastic x-ray scattering experiments with state-of-the-art ab initio many-body calculations, we investigate the electronic screening mechanisms in strongly correlated CuO in a large range of energy and momentum transfers. The excellent agreement between theory and experiment, including the low-energy charge excitations, allows us to use the calculated dynamical screening as a safe building block for many-body perturbation theory and to elucidate the crucial role played by d-d excitations in renormalizing the band gap of CuO. In this way we can dissect the contributions of different excitations to the electronic self-energy which is illuminating concerning both the general theory and this prototypical material.Peer reviewe
Inelastic X-ray scattering study of the collective dynamics in liquid sodium
Inelastic X-ray scattering data have been collected for liquid sodium at
T=390 K, i.e. slightly above the melting point. Owing to the very high
instrumental resolution, pushed up to 1.5 meV, it has been possible to
determine accurately the dynamic structure factor, , in a wide
wavevector range, nm, and to investigate on the dynamical
processes underlying the collective dynamics. A detailed analysis of the
lineshape of , similarly to other liquid metals, reveals the
co-existence of two different relaxation processes with slow and fast
characteristic timescales respectively. The present data lead to the conclusion
that: i) the picture of the relaxation mechanism based on a simple viscoelastic
model fails; ii) although the comparison with other liquid metals reveals
similar behavior, the data do not exhibit an exact scaling law as the principle
of corresponding state would predict.Comment: RevTex, 7 pages, 6 eps figures. Accepted by Phys. Rev.
Evidence of short time dynamical correlations in simple liquids
We report a molecular dynamics (MD) study of the collective dynamics of a
simple monatomic liquid -interacting through a two body potential that mimics
that of lithium- across the liquid-glass transition. In the glassy phase we
find evidences of a fast relaxation process similar to that recently found in
Lennard-Jones glasses. The origin of this process is ascribed to the
topological disorder, i.e. to the dephasing of the different momentum
Fourier components of the actual normal modes of vibration of the disordered
structure. More important, we find that the fast relaxation persists in the
liquid phase with almost no temperature dependence of its characteristic
parameters (strength and relaxation time). We conclude, therefore, that in the
liquid phase well above the melting point, at variance with the usual
assumption of {\it un-correlated} binary collisions, the short time particles
motion is strongly {\it correlated} and can be described via a normal mode
expansion of the atomic dynamics.Comment: 7 pages, 7 .eps figs. To appear in Phys. Rev.
Anomalous Dispersion of Longitudinal Optical Phonons in Determined by Inelastic X-ray Scattering
The phonon dispersions of along
the direction have been determined by inelastic x-ray scattering.
Compared to the undoped parent compound, the two highest longitudinal phonon
branches, associated with the Cu-O bond-stretching and out-of-plane oxygen
vibration, are shifted to lower energies. Moreover, an anomalous softening of
the bond-stretching band is observed around . These
signatures provide evidence for strong electron-phonon coupling in this
electron-doped high-temperature superconductor.Comment: 4 pages, 4 figure
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