12,466 research outputs found
Universal phase diagram of a strongly interacting Fermi gas with unbalanced spin populations
We present a theoretical interpretation of a recent experiment presented in
ref. \cite{Zwierlein06} on the density profile of Fermi gases with unbalanced
spin populations. We show that in the regime of strong interaction, the
boundaries of the three phases observed in \cite{Zwierlein06} can be
characterized by two dimensionless numbers and .
Using a combination of a variational treatment and a study of the experimental
results, we infer rather precise bounds for these two parameters.Comment: 4 pages, 2 figure
Attractive Fermi gases with unequal spin populations in highly elongated traps
We investigate two-component attractive Fermi gases with imbalanced spin
populations in trapped one dimensional configurations. The ground state
properties are determined within local density approximation, starting from the
exact Bethe-ansatz equations for the homogeneous case. We predict that the
atoms are distributed according to a two-shell structure: a partially polarized
phase in the center of the trap and either a fully paired or a fully polarized
phase in the wings. The partially polarized core is expected to be a superfluid
of the FFLO type. The size of the cloud as well as the critical spin
polarization needed to suppress the fully paired shell, are calculated as a
function of the coupling strength.Comment: Final accepted versio
A study of the nature of perceptual skills in relation to spelling and an analysis of spelling errors
Thesis (Ed.M.)--Boston Universit
Theory of the striped superconductor
We define a distinct phase of matter, a "pair density wave" (PDW), in which
the superconducting order parameter varies periodically as a function of
position such that when averaged over the center of mass position, all
components of vanish identically. Specifically, we study the simplest,
unidirectional PDW, the "striped superconductor," which we argue may be at the
heart of a number of spectacular experimental anomalies that have been observed
in the failed high temperature superconductor, La BaCuO. We
present a solvable microscopic model with strong electron-electron interactions
which supports a PDW groundstate. We also discuss, at the level of Landau
theory, the nature of the coupling between the PDW and other order parameters,
and the origins and some consequences of the unusual sensitivity of this state
to quenched disorder.Comment: 16 pages, 3 figures, 1 table; Journal ref. adde
Fermi-liquid effects in the Fulde-Ferrell-Larkin-Ovchinnikov state of two-dimensional d-wave superconductors
We study the effects of Fermi-liquid interactions on quasi-two-dimensional
d-wave superconductors in a magnetic field. The phase diagram of the
superconducting state, including the periodic Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) state in high magnetic fields, is discussed for different strengths of
quasiparticle many-body interactions within Landau's theory of Fermi liquids.
Decreasing the Fermi-liquid parameter causes the magnetic spin
susceptibility to increase, which in turn leads to a reduction of the FFLO
phase. It is shown that a negative results in a first-order phase
transition from the normal to the uniform superconducting state in a finite
temperature interval. Finally, we discuss the thermodynamic implications of a
first-order phase transition for CeCoIn.Comment: published version; removed direct comparison with experiment for the
upper critical field, as required by the referee
Finite-momentum Bose-Einstein condensates in shaken 2D square optical lattices
We consider ultracold bosons in a 2D square optical lattice described by the
Bose-Hubbard model. In addition, an external time-dependent sinusoidal force is
applied to the system, which shakes the lattice along one of the diagonals. The
effect of the shaking is to renormalize the nearest-neighbor hopping
coefficients, which can be arbitrarily reduced, can vanish, or can even change
sign, depending on the shaking parameter. It is therefore necessary to account
for higher-order hopping terms, which are renormalized differently by the
shaking, and introduce anisotropy into the problem. We show that the
competition between these different hopping terms leads to finite-momentum
condensates, with a momentum that may be tuned via the strength of the shaking.
We calculate the boundaries between the Mott-insulator and the different
superfluid phases, and present the time-of-flight images expected to be
observed experimentally. Our results open up new possibilities for the
realization of bosonic analogs of the FFLO phase describing inhomogeneous
superconductivity.Comment: 7 pages, 7 figure
Faint Field Galaxies Around Bright Stars - A New Strategy for Imaging at the Diffraction Limit
This paper presents a new strategy for observing faint galaxies with high
order natural guide star systems. We have imaged 5 high galactic latitude
fields within the isoplanatic patch of bright stars (8.5 < R < 10.3 mag). The
fields provide a rich set of faint field galaxies that are observable with a
natural guide star adaptive optics system on a large telescope. Due to the
small fields of many AO science cameras, these preliminary images are necessary
to identify candidate galaxies. We present the photometry and positions for 78
objects (at least 40 galaxies) near five bright stars, appropriate for
diffraction limited studies with the Keck and other AO systems on large
ground-based telescopes. The K band seeing conditions in each field were
excellent (0.4" - 0.7") allowing us to identify stars and estimate galaxy
sizes. We also simulate AO images of field galaxies to determine the
feasibility of infrared morphological studies at the diffraction limit. With
new high order AO systems coming on line with 8-10 meter class telescopes, we
believe these observations are invaluable in beginning to study faint galaxy
populations at the diffraction limit.Comment: 15 pages, Latex, 9 figures. Accepted for publication in P.A.S.
Profiles of near-resonant population-imbalanced trapped Fermi gases
We investigate the density profiles of a partially polarized trapped Fermi
gas in the BCS-BEC crossover region using mean field theory within the local
density approximation. Within this approximation the gas is phase separated
into concentric shells. We describe how the structure of these shells depends
upon the polarization and the interaction strength. A Comparison with
experiments yields insight into the possibility of a polarized superfluid
phase.Comment: 4 pages, 5 Figures, Published versio
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