2,644 research outputs found
Importance of interorbital charge transfers for the metal-to-insulator transition of BaVS
The underlying mechanism of the metal-to-insulator transition (MIT) in
BaVS is investigated, using dynamical mean-field theory in combination with
density functional theory. It is shown that correlation effects are responsible
for a strong charge redistribution, which lowers the occupancy of the broader
\a1g band in favor of the narrower bands. This resolves several
discrepancies between band theory and the experimental findings, such as the
observed value of the charge-density wave ordering vector associated with the
MIT, and the presence of local moments in the metallic phase.Comment: improved discussion, new figure, added reference
The alpha-gamma transition of Cerium is entropy-driven
We emphasize, on the basis of experimental data and theoretical calculations,
that the entropic stabilization of the gamma-phase is the main driving force of
the alpha-gamma transition of cerium in a wide temperature range below the
critical point. Using a formulation of the total energy as a functional of the
local density and of the f-orbital local Green's functions, we perform
dynamical mean-field theory calculations within a new implementation based on
the multiple LMTO method, which allows to include semi-core states. Our results
are consistent with the experimental energy differences and with the
qualitative picture of an entropy-driven transition, while also confirming the
appearance of a stabilization energy of the alpha phase as the quasiparticle
Kondo resonance develops.Comment: 5 pages, 6 figure
Is the Mott transition relevant to f-electron metals ?
We study how a finite hybridization between a narrow correlated band and a
wide conduction band affects the Mott transition. At zero temperature, the
hybridization is found to be a relevant perturbation, so that the Mott
transition is suppressed by Kondo screening. In contrast, a first-order
transition remains at finite temperature, separating a local moment phase and a
Kondo- screened phase. The first-order transition line terminates in two
critical endpoints. Implications for experiments on f-electron materials such
as the Cerium alloy CeLaTh are discussed.Comment: 5 pages, 3 figure
Thermal evolution of the primordial clouds in warm dark matter models with keV sterile neutrinos
We analyze the processes relevant for star formation in a model with dark
matter in the form of sterile neutrinos. Sterile neutrino decays produce an
X-ray background radiation that has a two-fold effect on the collapsing clouds
of hydrogen. First, the X-rays ionize the gas and cause an increase in the
fraction of molecular hydrogen, which makes it easier for the gas to cool and
to form stars. Second, the same X-rays deposit a certain amount of heat, which
could, in principle, thwart the cooling of gas. We find that, in all the cases
we have examined, the overall effect of sterile dark matter is to facilitate
the cooling of gas. Hence, we conclude that dark matter in the form of sterile
neutrinos can help the early collapse of gas clouds and the subsequent star
formation.Comment: aastex, 31 pages, 4 figures; one figure and some references added,
minor changes in the text; to appear in Astrophysical Journa
Orbital selective Mott transition in multi-band systems: slave-spin representation and dynamical mean-field theory
We examine whether the Mott transition of a half-filled, two-orbital Hubbard
model with unequal bandwidths occurs simultaneously for both bands or whether
it is a two-stage process in which the orbital with narrower bandwith localizes
first (giving rise to an intermediate `orbital-selective' Mott phase). This
question is addressed using both dynamical mean-field theory, and a
representation of fermion operators in terms of slave quantum spins, followed
by a mean-field approximation (similar in spirit to a Gutzwiller
approximation). In the latter approach, the Mott transition is found to be
orbital-selective for all values of the Coulomb exchange (Hund) coupling J when
the bandwidth ratio is small, and only beyond a critical value of J when the
bandwidth ratio is larger. Dynamical mean-field theory partially confirms these
findings, but the intermediate phase at J=0 is found to differ from a
conventional Mott insulator, with spectral weight extending down to arbitrary
low energy. Finally, the orbital-selective Mott phase is found, at
zero-temperature, to be unstable with respect to an inter-orbital
hybridization, and replaced by a state with a large effective mass (and a low
quasiparticle coherence scale) for the narrower band.Comment: Discussion on the effect of hybridization on the OSMT has been
extende
Modification of classical electron transport due to collisions between electrons and fast ions
A Fokker-Planck model for the interaction of fast ions with the thermal
electrons in a quasi-neutral plasma is developed. When the fast ion population
has a net flux (i.e. the distribution of the fast ions is anisotropic in
velocity space) the electron distribution function is significantly perturbed
from Maxwellian by collisions with the fast ions, even if the fast ion density
is orders of magnitude smaller than the electron density. The Fokker-Planck
model is used to derive classical electron transport equations (a generalized
Ohm's law and a heat flow equation) that include the effects of the
electron-fast ion collisions. It is found that these collisions result in a
current term in the transport equations which can be significant even when
total current is zero. The new transport equations are analyzed in the context
of a number of scenarios including particle heating in ICF and MIF
plasmas and ion beam heating of dense plasmas
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