5,930 research outputs found
Exotic paired phases in ladders with spin-dependent hopping
Fermions in two-dimensions (2D) when subject to anisotropic spin-dependent
hopping can potentially give rise to unusual paired states in {\it unpolarized}
mixtures that can behave as non-Fermi liquids. One possibility is a fully
paired state with a gap for fermion excitations in which the Cooper pairs
remain uncondensed. Such a "Cooper-pair Bose-metal" phase would be expected to
have a singular Bose-surface in momentum space. As demonstrated in the context
of 2D bosons hopping with a frustrating ring-exchange interaction, an analogous
Bose-metal phase has a set of quasi-1D descendent states when put on a ladder
geometry. Here we present a density matrix renormalization group (DMRG) study
of the attractive Hubbard model with spin-dependent hopping on a two-leg ladder
geometry. In our setup, one spin species moves preferentially along the leg
direction, while the other does so along the rung direction. We find compelling
evidence for the existence of a novel Cooper-pair Bose-metal phase in a region
of the phase diagram at intermediate coupling. We further explore the phase
diagram of this model as a function of hopping anisotropy, density, and
interaction strength, finding a conventional superfluid phase, as well as a
phase of paired Cooper pairs with d-wave symmetry, similar to the one found in
models of hard-core bosons with ring-exchange. We argue that simulating this
model with cold Fermi gases on spin dependent optical lattices is a promising
direction for realizing exotic quantum states.Comment: 10 pages, 12 figure
Two-dimensional chiral crystals in the NJL model
We investigate the phase structure of the Nambu--Jona-Lasinio model at zero
temperature, allowing for a two-dimensional spatial dependence of the chiral
condensate. Applying the mean-field approximation, we consider various periodic
structures with rectangular and hexagonal geometries, and minimize the
corresponding free energy. We find that these two-dimensional chiral crystals
are favored over homogeneous phases in a certain window in the region where the
phase transition would take place when the analysis was restricted to
homogeneous condensates. It turns out, however, that in this regime they are
disfavored against a phase with a one-dimensional modulation of the chiral
condensate. On the other hand, we find that square and hexagonal lattices
eventually get favored at higher chemical potentials. Although stretching the
limits of the model to some extent, this would support predictions from
quarkyonic-matter studies.Comment: 12 pages, 6 figures. v2: added figure, small modifications, matches
published versio
Suppression or enhancement of the Fulde-Ferrell-Larkin-Ovchinnikov order in a one-dimensional optical lattice with particle correlated tunnelling
We study through controlled numerical simulation the ground state properties
of spin-polarized strongly interacting fermi gas in an anisotropic optical
lattice, which is described by an effective one-dimensional general Hubbard
model with particle correlated hopping rate. We show that the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type of state, while enhanced by a
negative correlated hopping rate, can be completely suppressed by positive
particle correlated hopping, yielding to an unusual magnetic phase even for
particles with on-site attractive interaction We also find several different
phase separation patterns for these atoms in an inhomogeneous harmonic trap,
depending on the correlated hopping rate
Detecting the breached pair phase in a polarized ultracold Fermi gas
We propose a method for the experimental detection of a new quantum phase,
the breached pair state, in a strongly interacting ultracold Fermi gas with
population imbalance. We show that through the time-of-flight Raman imaging,
the presence of such a phase can be unambiguously determined with a measurement
of the momentum-space phase separation of the minority spin component. To guide
the experimental efforts, the momentum-space density profiles are calculated
under typical experimental conditions.Comment: 4 pages, 3 figures, replaced with the published versio
Trapped Fermions across a Feshbach resonance with population imbalance
We investigate the phase separation of resonantly interacting fermions in a
trap with imbalanced spin populations, both at zero and at finite temperatures.
We directly minimize the thermodynamical potential under the local density
approximation instead of using the gap equation, as the latter may give
unstable solutions. On the BEC side of the resonance, one may cross three
different phases from the trap center to the edge; while on the BCS side or at
resonance, typically only two phases show up. We compare our results with the
recent experiment, and the agreement is remarkable.Comment: 4 pages, 3 figures, replaced with the published versio
Stripe, checkerboard, and liquid-crystal ordering from anisotropic p-orbital Fermi surfaces in optical lattices
We study instabilities of single-species fermionic atoms in the p-orbital
bands in two-dimensional optical lattices at noninteger filling against
interactions. Charge density wave and orbital density wave orders with stripe
or checkerboard patterns are found for attractive and repulsive interactions,
respectively. The superfluid phase, usually expected of attractively
interacting fermions, is strongly suppressed. We also use field theory to
analyze the possible phase-transitions from orbital stripe order to
liquid-crystal phases and obtain the phase diagram. The condition of
nearly-perfect Fermisurface nesting, which is key to the above results, is
shown robustly independent of fermion fillings in such p-orbital systems, and
the momentum of density wave oscillation is highly tunable.
Such remarkable features show the promise of making those exotic orbital
phases, which are of broad interest in condensed-matter physics, experimentally
realizable with optical lattice gases.Comment: final version, 8 pages, 5 figure
Observation of Phase Separation in a Strongly-Interacting Imbalanced Fermi Gas
We have observed phase separation between the superfluid and the normal
component in a strongly interacting Fermi gas with imbalanced spin populations.
The in situ distribution of the density difference between two trapped spin
components is obtained using phase-contrast imaging and 3D image
reconstruction. A shell structure is clearly identified where the superfluid
region of equal densities is surrounded by a normal gas of unequal densities.
The phase transition induces a dramatic change in the density profiles as
excess fermions are expelled from the superfluid.Comment: 5 pages, 7 figure
Induced superfluidity of imbalanced Fermi gases near unitarity
The induced intraspecies interactions among the majority species, mediated by
the minority species, is computed for a population-imbalanced two-component
Fermi gas. Although the Feshbach-resonance mediated interspecies interaction is
dominant for equal populations, leading to singlet s-wave pairing, we find that
in the strongly imbalanced regime the induced intraspecies interaction leads to
p-wave pairing and superfluidity of the majority species. Thus, we predict that
the observed spin-polaron Fermi liquid state in this regime is unstable to
p-wave superfluidity, in accordance with the results of Kohn and Luttinger,
below a temperature that, near unitarity, we find to be within current
experimental capabilities. Possible experimental signatures of the p-wave state
using radio-frequency spectroscopy as well as density-density correlations
after free expansion are presented.Comment: 15 pages, 13 figures, submitted to Phys. Rev.
- …