5,019 research outputs found
Critical frequency for vortex nucleation in Bose-Fermi mixtures in optical lattices
We investigate within mean-field theory the influence of a one-dimensional
optical lattice and of trapped degenerate fermions on the critical rotational
frequency for vortex line creation in a Bose-Einstein condensate. We consider
laser intensities of the lattice such that quantum coherence across the
condensate is ensured. We find a sizable decrease of the thermodynamic critical
frequency for vortex nucleation with increasing applied laser strength and
suggest suitable parameters for experimental observation. Since 87Rb-40K
mixtures may undergo collapse, we analyze the related question of how the
optical lattice affects the mechanical stability of the system.Comment: 5 pages, 4 figures, revtex
Incommensurate spin correlations in highly oxidized cobaltates LaSrCoO
We observe quasi-static incommensurate magnetic peaks in neutron scattering
experiments on layered cobalt oxides La2-xSrxCoO4 with high Co oxidation states
that have been reported to be paramagnetic. This enables us to measure the
magnetic excitations in this highly hole-doped incommensurate regime and
compare our results with those found in the low-doped incommensurate regime
that exhibit hourglass magnetic spectra. The hourglass shape of magnetic
excitations completely disappears given a high Sr doping. Moreover, broad
low-energy excitations are found, which are not centered at the incommensurate
magnetic peak positions but around the quarter-integer values that are
typically exhibited by excitations in the checkerboard charge ordered phase.
Our findings suggest that the strong inter-site exchange interactions in the
undoped islands are critical for the emergence of hourglass spectra in the
incommensurate magnetic phases of La2-xSrxCoO4.Comment: http://www.nature.com/articles/srep25117
Intricacies of the Co spin state in SrCoIrO: an x-ray absorption and magnetic circular dichroism study
We report on a combined soft x-ray absorption and magnetic circular dichroism
(XMCD) study at the Co- on the hybrid 3/5 solid state oxide
SrCoIrO with the KNiF structure. Our data
indicate unambiguously a pure high spin state for the Co
(3) ions with a significant unquenched orbital moment
despite the sizeable elongation of the CoO octahedra. Using quantitative
model calculations based on parameters consistent with our spectra, we have
investigated the stability of this high spin state with respect to the
competing low spin and intermediate spin states.Comment: 7 pages, 4 figure
Overture - Object-oriented tools for overset grid applications
The Overture framework is an object-oriented environment for solving partial differential equations in two and three space dimensions. It is a collection of C++ libraries that enables the use of finite difference and finite volume methods at a level that hides the details of the associated data structures. Overture can be used to solve problems in complicated, moving geometries using the method of overlapping grids. It has support for grid generation, difference operators, boundary conditions, data-base access and graphics. Short sample code segments are presented to show the power of this approach
Bose-Fermi Mixtures in Optical Lattices
Using mean field theory, we have studied Bose-Fermi mixtures in a
one-dimensional optical lattice in the case of an attractive boson-fermion
interaction. We consider that the fermions are in the degenerate regime and
that the laser intensities are such that quantum coherence across the
condensate is ensured. We discuss the effect of the optical lattice on the
critical rotational frequency for vortex line creation in the Bose-Einstein
condensate, as well as how it affects the stability of the boson-fermion
mixture. A reduction of the critical frequency for nucleating a vortex is
observed as the strength of the applied laser is increased. The onset of
instability of the mixture occurs for a sizeably lower number of fermions in
the presence of a deep optical lattice.Comment: 7 pages, 6 figures, revtex4, 14th International Laser Physics
Workshop (LPHYS'05
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