6,745 research outputs found
Ultrafast demagnetization in bulk versus thin films: An ab initio study
We report on {\it ab-initio} simulations of the quantum dynamics of
electronic charge and spin when subjected to intense laser pulses. By
performing separate calculations for a Ni thin film and bulk Ni, we conclude
that surface effects have a dramatic influence on amplifying the laser induced
demagnetization. We show that the reason for this amplification is due to
increased spin-currents on the surface of the thin film. This enhancement is a
direct consequence of the broken symmetry originating from the surface
formation. We find that the underlying physics of demagnetization, during the
early femtoseconds, for both bulk and thin film is dominated by spin-flips
induced by spin-orbit coupling. After the first fs this changes in
that the dominant cause of demagnetization is the flow of spin-currents, which
leads to stronger demagnetization in the film compared to that of the bulk.Comment: 12 pages, 3 figure
Parameterized optimized effective potential for atoms
The optimized effective potential equations for atoms have been solved by
parameterizing the potential. The expansion is tailored to fulfill the known
asymptotic behavior of the effective potential at both short and long
distances. Both single configuration and multi configuration trial wave
functions are implemented. Applications to several atomic systems are presented
improving previous works. The results here obtained are very close to those
calculated in either the Hartree-Fock and the multi configurational
Hartree-Fock framework.Comment: 8 pages, 3 figure
Analysis of OPM potentials for multiplet states of 3d transition metal atoms
We apply the optimized effective potential method (OPM) to the multiplet
energies of the 3d transition metal atoms, where the orbital dependence of
the energy functional with respect to orbital wave function is the
single-configuration HF form. We find that the calculated OPM exchange
potential can be represented by the following two forms. Firstly, the
difference between OPM exchange potentials of the multiplet states can be
approximated by the linear combination of the potentials derived from the
Slater integrals and for the average
energy of the configuration. Secondly, the OPM exchange potential can be
expressed as the linear combination of the OPM exchange potentials of the
single determinants.Comment: 15 pages, 6 figures, to be published in J. Phys.
A Centre-Stable Manifold for the Focussing Cubic NLS in
Consider the focussing cubic nonlinear Schr\"odinger equation in : It admits special solutions of the form
, where is a Schwartz function and a positive
() solution of The space of
all such solutions, together with those obtained from them by rescaling and
applying phase and Galilean coordinate changes, called standing waves, is the
eight-dimensional manifold that consists of functions of the form . We prove that any solution starting
sufficiently close to a standing wave in the norm and situated on a certain codimension-one local
Lipschitz manifold exists globally in time and converges to a point on the
manifold of standing waves. Furthermore, we show that \mc N is invariant
under the Hamiltonian flow, locally in time, and is a centre-stable manifold in
the sense of Bates, Jones. The proof is based on the modulation method
introduced by Soffer and Weinstein for the -subcritical case and adapted
by Schlag to the -supercritical case. An important part of the proof is
the Keel-Tao endpoint Strichartz estimate in for the nonselfadjoint
Schr\"odinger operator obtained by linearizing around a standing wave solution.Comment: 56 page
A combined particle trap/HTDMA hygroscopicity study of mixed inorganic/organic aerosol particles
International audienceAtmospheric aerosols are often mixtures of inorganic and organic material. Organics can represent a large fraction of the total aerosol mass and are comprised of water-soluble and insoluble compounds. Increasing attention was paid in the last decade to the capability of mixed inorganic/organic aerosol particles to take up water (hygroscopicity). We performed hygroscopicity measurements of internally mixed particles containing ammonium sulfate and carboxylic acids (citric, glutaric, adipic acid) in parallel with an electrodynamic balance (EDB) and a hygroscopicity tandem differential mobility analyzer (HTDMA). The organic compounds were chosen to represent three distinct physical states. During hygroscopicity cycles covering hydration and dehydration measured by the EDB and the HTDMA, pure citric acid remained always liquid, adipic acid remained always solid, while glutaric acid could be either. We show that the hygroscopicity of mixtures of the above compounds is well described by the Zdanovskii-Stokes-Robinson (ZSR) relationship as long as the two-component particle is completely liquid in the ammonium sulfate/citric acid and in the ammonium sulfate/glutaric acid cases. However, we observe significant discrepancies compared to what is expected from bulk thermodynamics when a solid component is present. We explain this in terms of a complex morphology resulting from the crystallization process leading to veins, pores, and grain boundaries which allow for water sorption in excess of bulk thermodynamic predictions caused by the inverse Kelvin effect on concave surfaces
Three-Dimensional Fermi Surface of Overdoped La-Based Cuprates
We present a soft x-ray angle-resolved photoemission spectroscopy study of
the overdoped high-temperature superconductors LaSrCuO and
LaEuSrCuO. In-plane and out-of-plane components of
the Fermi surface are mapped by varying the photoemission angle and the
incident photon energy. No dispersion is observed along the nodal
direction, whereas a significant antinodal dispersion is identified.
Based on a tight-binding parametrization, we discuss the implications for the
density of states near the van-Hove singularity. Our results suggest that the
large electronic specific heat found in overdoped LaSrCuO can
not be assigned to the van-Hove singularity alone. We therefore propose quantum
criticality induced by a collapsing pseudogap phase as a plausible explanation
for observed enhancement of electronic specific heat
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