7,609 research outputs found
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
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
Competition between Normal Superfluidity and Larkin-Ovchinnikov Phases of Polarized Fermi Gases in Elongated Traps
By applying the recently proposed antisymmetric superfluid local density
approximation (ASLDA) to strongly interacting polarized atomic gases at
unitarity in very elongated traps, we find families of Larkin-Ovchinnikov (LO)
type of solutions with prominent transversal oscillation of pairing potential.
These LO states coexist with a superfluid state having a smooth pairing
potential. We suggest that the LO phase could be accessible experimentally by
increasing adiabatically the trap aspect ratio. We show that the local
asymmetry effects contained in ASLDA do not support a deformed superfluid core
predicted by previous Bogoliubov-de Gennes treatments.Comment: 4 pages, 4 figures; revision; accepted for publication in Phys.Rev.A
(Rapid Communication
Interplay between phase defects and spin polarization in the specific heat of the spin density wave compound (TMTTF)_2Br in a magnetic field
Equilibrium heat relaxation experiments provide evidence that the ground
state of the commensurate spin density wave (SDW) compound (TMTTF)Br after
the application of a sufficient magnetic field is different from the
conventional ground state. The experiments are interpreted on the basis of the
local model of strong pinning as the deconfinement of soliton-antisoliton pairs
triggered by the Zeeman coupling to spin degrees of freedom, resulting in a
magnetic field induced density wave glass for the spin carrying phase
configuration.Comment: 4 pages, 5 figure
Resonant pairing between Fermions with unequal masses
We study the pairing between Fermions of different masses, especially at the
unitary limit. At equal populations, the thermodynamic properties are identical
with the equal mass case provided an appropriate rescaling is made. At unequal
populations, for sufficiently light majority species, the system does not phase
separate. For sufficiently heavy majority species, the phase separated normal
phase have a density larger than that of the superfluid. For atoms in harmonic
traps, the density profiles for unequal mass Fermions can be drastically
different from their equal-mass counterparts.Comment: 10 pages, 4 figure
Integral Field Spectroscopy of High-Redshift Star Forming Galaxies with Laser Guided Adaptive Optics: Evidence for Dispersion-Dominated Kinematics
We present early results from an ongoing study of the kinematic structure of
star-forming galaxies at redshift z ~ 2 - 3 using integral-field spectroscopy
of rest-frame optical nebular emission lines in combination with Keck laser
guide star adaptive optics (LGSAO). We show kinematic maps of 3 target galaxies
Q1623-BX453, Q0449-BX93, and DSF2237a-C2 located at redshifts z = 2.1820,
2.0067, and 3.3172 respectively, each of which is well-resolved with a PSF
measuring approximately 0.11 - 0.15 arcsec (~ 900 - 1200 pc at z ~ 2-3) after
cosmetic smoothing. Neither galaxy at z ~ 2 exhibits substantial kinematic
structure on scales >~ 30 km/s; both are instead consistent with largely
dispersion-dominated velocity fields with sigma ~ 80 km/s along any given line
of sight into the galaxy. In contrast, DSF2237a-C2 presents a well-resolved
gradient in velocity over a distance of ~ 4 kpc with peak-to-peak amplitude of
140 km/s. It is unlikely that DSF2237a-C2 represents a dynamically cold
rotating disk of ionized gas as the local velocity dispersion of the galaxy
(sigma = 79 km/s) is comparable to the observed shear. Using extant
multi-wavelength spectroscopy and photometry we relate these kinematic data to
physical properties such as stellar mass, gas fraction, star formation rate,
and outflow kinematics and consider the applicability of current galaxy
formation models.[Abridged]Comment: 19 pages, 10 figures (5 color); accepted for publication in ApJ.
Version with full-resolution figures is available at
http://www.astro.caltech.edu/~drlaw/Papers/OSIRIS_data1.pd
Itinerant ferromagnetism in an interacting Fermi gas with mass imbalance
We study the emergence of itinerant ferromagnetism in an ultra-cold atomic
gas with a variable mass ratio between the up and down spin species. Mass
imbalance breaks the SU(2) spin symmetry leading to a modified Stoner
criterion. We first elucidate the phase behavior in both the grand canonical
and canonical ensembles. Secondly, we apply the formalism to a harmonic trap to
demonstrate how a mass imbalance delivers unique experimental signatures of
ferromagnetism. These could help future experiments to better identify the
putative ferromagnetic state. Furthermore, we highlight how a mass imbalance
suppresses the three-body loss processes that handicap the formation of a
ferromagnetic state. Finally, we study the time dependent formation of the
ferromagnetic phase following a quench in the interaction strength
Stability of the Breached Pair State for a Two-species Fermionic System in the Presence of Feshbach Resonance
We investigate the phenomenon of fermionic pairing with mismatched Fermi
surfaces in a two-species system in the presence of Feshbach resonance, where
the resonantly-paired fermions combine to form bosonic molecules. We observe
that the Feshbach parameters control the critical temperature of the gapped BCS
superfluid state, and also determine the range over which a gapless breached
pair state may exist. Demanding the positivity of the superfluid density, it is
shown that although a breached pair state with two Fermi surfaces is always
unstable, its single Fermi-surface counterpart can be stable if the chemical
potentials of the two pairing species have opposite signs. This condition is
satisfied only over a narrow region in the BEC side, characterized by an upper
and a lower limit for the magnetic field. We estimate these limits for a
mixture of two hyperfine states of Li using recent experimental data.Comment: 14 pages,5 figure
Kondo Breakdown and Hybridization Fluctuations in the Kondo-Heisenberg Lattice
We study the deconfined quantum critical point of the Kondo-Heisenberg
lattice in three dimensions using a fermionic representation for the localized
spins. The mean-field phase diagram exhibits a zero temperature quantum
critical point separating a spin liquid phase where the hybridization vanishes
and a Kondo phase where it does not. Two solutions can be stabilized in the
Kondo phase, namely a uniform hybridization when the band masses of the
conduction electrons and the spinons have the same sign, and a modulated one
when they have opposite sign. For the uniform case, we show that above a very
small temperature scale, the critical fluctuations associated with the
vanishing hybridization have dynamical exponent z=3, giving rise to a
resistivity that has a T log T behavior. We also find that the specific heat
coefficient diverges logarithmically in temperature, as observed in a number of
heavy fermion metals.Comment: new Figure 2, new results on spin susceptibility, some minor changes
to tex
Superfluid stability in BEC-BCS crossover
We consider a dilute atomic gas of two species of fermions with unequal
concentrations under a Feshbach resonance. We find that the system can have
distinct properties due to the unbound fermions. The uniform state is stable
only when either (a) beyond a critical coupling strength, where it is a gapless
superfluid, or (b) when the coupling strength is sufficiently weak, where it is
a normal Fermi gas mixture. Phase transition(s) must therefore occur when the
resonance is crossed.Comment: 4 pages, 4 figure
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