592 research outputs found
Plasmons in Sodium under Pressure: Increasing Departure from Nearly-Free-Electron Behavior
We have measured plasmon energies in Na under high pressure up to 43 GPa
using inelastic x-ray scattering (IXS). The momentum-resolved results show
clear deviations, growing with increasing pressure, from the predictions for a
nearly-free electron metal. Plasmon energy calculations based on
first-principles electronic band structures and a quasi-classical plasmon model
allow us to identify a pressure-induced increase in the electron-ion
interaction and associated changes in the electronic band structure as the
origin of these deviations, rather than effects of exchange and correlation.
Additional IXS results obtained for K and Rb are addressed briefly.Comment: 5 pages, 4 figure
Liquid-like behavior of supercritical fluids
The high frequency dynamics of fluid oxygen have been investigated by
Inelastic X-ray Scattering. In spite of the markedly supercritical conditions
(, ), the sound velocity exceeds the hydrodynamic
value of about 20%, a feature which is the fingerprint of liquid-like dynamics.
The comparison of the present results with literature data obtained in several
fluids allow us to identify the extrapolation of the liquid vapor-coexistence
line in the (, ) plane as the relevant edge between liquid- and
gas-like dynamics. More interestingly, this extrapolation is very close to the
non metal-metal transition in hot dense fluids, at pressure and temperature
values as obtained by shock wave experiments. This result points to the
existence of a connection between structural modifications and transport
properties in dense fluids.Comment: 4 pages, 3 figures, accepted by Phys. Rev. Let
Thin Shell Dynamics and Equations of State
A relation between stress-energy and motion is derived for accelerated Israel
layers. The relation, for layers between two Schwarzschild manifolds,
generalizes the equation of state for geodesic collapse. A set of linked layers
is discussed
Electron-phonon interaction in n-doped cuprates: an Inelastic X-ray Scattering study
Inelastic x-ray scattering (IXS) with very high (meV) energy resolution has
become a valuable spectroscopic tool, complementing the well established
coherent inelastic neutron scattering (INS) technique for phonon dispersion
investigations. In the study of crystalline systems IXS is a viable alternative
to INS, especially in cases where only small samples are available. Using IXS,
we have measured the phonon dispersion of Nd_{1.86}Ce_{0.14}CuO_{4+\delta}
along the [x,0,0] and [x,x,0] in-plane directions. Compared to the undoped
parent compound, the two highest longitudinal optical (LO) phonon branches are
shifted to lower energies because of Coulomb-screening effects brought about by
the doped charge carriers. An additional anomalous softening of the highest
branch is observed around q=(0.2,0,0). This anomalous softening, akin to what
has been observed in other compounds, provides evidence for a strong
electron-phonon coupling in the electron-doped high-temperature
superconductors.Comment: Proceedings of the SATT11 conference, Vietri sul Mare - Italy (March
2002); accepted for publication on Int. J. Mod. Phys.
Bond stretching phonon softening and angle-resolved photoemission kinks in optimally doped Bi2Sr1.6La0.4Cu2O6 superconductors
We report the first measurement of the optical phonon dispersion in optimally
doped single layer Bi2Sr1.6La0.4Cu2O6+delta using inelastic x-ray scattering.
We found a strong softening of the Cu-O bond stretching phonon at about
q=(0.25,0,0) from 76 to 60 meV, similar to the one reported in other cuprates.
A direct comparison with angle-resolved photoemission spectroscopy measurements
taken on the same sample, revealed an excellent agreement in terms of energy
and momentum between the ARPES nodal kink and the soft part of the bond
stretching phonon. Indeed, we find that the momentum space where a 63 meV kink
is observed can be connected with a vector q=(xi,0,0) with xi~0.22, which
corresponds exactly to the soft part of the bond stretching phonon mode. This
result supports an interpretation of the ARPES kink in terms of electron-phonon
coupling.Comment: submited to PR
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