1,910 research outputs found
Superfluid phases of fermions with hybridized and orbitals
We explore the superfluid phases of a two-component Fermi mixture with
hybridized orbitals in optical lattices. We show that there exists a general
mapping of this system to the Lieb lattice. By using simple multiband models
with hopping between and -orbital states, we show that superfluid order
parameters can have a -phase difference between lattice sites, which is
distinct from the case with hopping between -orbitals. If the population
imbalance between the two spin species is tuned, the superfluid phase may
evolve through various phases due to the interplay between hopping,
interactions and imbalance. We show that the rich behavior is observable in
experimentally realizable systems.Comment: 13 pages, 11 figures. Published versio
Spontaneous squeezing of a vortex in an optical lattice
We study the equilibrium states of a vortex in a Bose-Einstein condensate in
a one-dimensional optical lattice. We find that quantum effects can be
important and that it is even possible for the vortex to be strongly squeezed,
which reflects itself in a different quantum mechanical uncertainty of the
vortex position in two orthogonal directions. The latter is observable by
measuring the atomic density after an expansion of the Bose-Einstein condensate
in the lattice.Comment: 8 pages, 3 figures, more details added, some new citation
Kelvin-Helmholtz instability in two-component Bose gases on a lattice
We explore the stability of the interface between two phase-separated Bose
gases in relative motion on a lattice. Gross-Pitaevskii-Bogoliubov theory and
the Gutzwiller ansatz are employed to study the short- and long-time stability
properties. The underlying lattice introduces effects of discreteness, broken
spatial symmetry, and strong correlations, all three of which are seen to have
considerable qualitative effects on the Kelvin-Helmholtz instability.
Discreteness is found to stabilize low flow velocities, because of the finite
energy associated with displacing the interface. Broken spatial symmetry
introduces a dependence not only on the relative flow velocity, but on the
absolute velocities. Strong correlations close to a Mott transition will stop
the Kelvin-Helmholtz instability from affecting the bulk density and creating
turbulence; instead, the instability will excite vortices with Mott-insulator
filled cores.Comment: 11 pages, 11 figure
Quantum fluctuations of a vortex in an optical lattice
Using a variational ansatz for the wave function of the Bose-Einstein
condensate, we develop a quantum theory of vortices and quadrupole modes in a
one-dimensional optical lattice. We study the coupling between the quadrupole
modes and Kelvin modes, which turns out to be formally analogous to the theory
of parametric processes in quantum optics. This leads to the possibility of
squeezing vortices. We solve the quantum multimode problem for the Kelvin modes
and quadrupole modes numerically and find properties that cannot be explained
with a simple linear-response theory.Comment: final version, minor change
Interband physics in an ultra-cold Fermi gas in an optical lattice
We study a gas of strongly polarized cold fermions in an optical lattice when
the excited p-bands are populated. We derive the relevant Hamiltonian and
discuss the expected phase diagram for both repulsive and attractive
interactions. In the parameter regime covered here, checkerboard
anti-ferromagnetic ordering is found to be possible for repulsive interactions
while for attractive interactions, transitions between different types of
paired phases are predicted.Comment: 5 pages, 2 figure
Nuclear antiferromagnetism in rhodium metal at positive and negative nanokelvin temperatures
We have measured the dynamic susceptibility of polycrystalline rhodium foils down to 280 pK and up to -750 pK. These record-low and -high nuclear spin temperatures were reached by adiabatic demagnetization using initial polarizations of 83 and -60%. At T>0, the static susceptibility, integrated from NMR spectra, displays an antiferromagnetic Curie-Weiss law, with Īø=-1.8Ā±0.3 nK. At T<0, a crossover from ferro- to antiferromagnetic tendency is found around -6 nK. We obtain Jnn/h=-17Ā±3 Hz and Jnnn/h=10Ā±3 Hz if only nearest and next nearest neighbor interactions are assumed.Peer reviewe
Socioeconomic Inequalities in Mortality Rates in Old Age in the World Health Organization Europe Region
Socioeconomic adversity is among the foremost fundamental causes of human suffering, and this is no less true in old age. Recent reports on socioeconomic inequalities in mortality rate in old age suggest that a low socioeconomic position continues to increase the risk of death even among the oldest old. We aimed to examine the evidence for socioeconomic mortality rate inequalities in old age, including information about associations with various indicators of socioeconomic position and for various geographic locations within the World Health Organization Region for Europe. The articles included in this review leave no doubt that inequalities in mortality rate by socioeconomic position persist into the oldest ages for both men and women in all countries for which information is available, although the relative risk measures observed were rarely higher than 2.00. Still, the available evidence base is heavily biased geographically, inasmuch as it is based largely on national studies from Nordic and Western European countries and local studies from urban areas in Southern Europe. This bias will hamper the design of European-wide policies to reduce inequalities in mortality rate. We call for a continuous update of the empiric evidence on socioeconomic inequalities in mortality rate
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