5,286 research outputs found
Finite temperature phase diagram of a polarized Fermi gas in an optical lattice
We present phase diagrams for a polarized Fermi gas in an optical lattice as
a function of temperature, polarization, and lattice filling factor. We
consider the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO), Sarma or breached pair
(BP), and BCS phases, and the normal state and phase separation. We show that
the FFLO phase appears in a considerable portion of the phase diagram. The
diagrams have two critical points of different nature. We show how various
phases leave clear signatures to momentum distributions of the atoms which can
be observed after time of flight expansion.Comment: Journal versio
Neutrality of a magnetized two-flavor quark superconductor
We investigate the effect of electric and color charge neutrality on the
two-flavor color superconducting (2SC) phase of cold and dense quark matter in
presence of constant external magnetic fields and at moderate baryon densities.
Within the framework of the Nambu-Jona-Lasinio (NJL) model, we study the
inter-dependent evolution of the quark's BCS gap and constituent mass with
increasing density and magnetic field. While confirming previous results
derived for the highly magnetized 2SC phase with color neutrality alone, we
obtain new results as a consequence of imposing charge neutrality. In the
charge neutral gapless 2SC phase (g2SC), a large magnetic field drives the
color superconducting phase transition to a crossover, while the chiral phase
transition is first order. At larger diquark-to-scalar coupling ratio
, where the 2SC phase is preferred, we see hints of the
Clogston-Chandrasekhar limit at a very large value of the magnetic field
(G), but this limit is strongly affected by Shubnikov de
Haas-van Alphen oscillations of the gap, indicating the transition to a
domain-like state.Comment: 19 pages, 7 figures, Matches with the published versio
Topological Structure of a Vortex in Fulde-Ferrell-Larkin-Ovchinnikov State
We find theoretically that the vortex core in the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is quite different from the
ordinary core by a simple topological reason. The intersection point of a
vortex and nodal plane of the FFLO state empties the excess spins. This leads
to observable consequences in the spatial structure of the spontaneous
magnetization. We analyze this topological structure based on the low lying
excitation spectrum by solving microscopic Bogoliubov-de Gennes equation to
clarify its physical origin.Comment: 4 pages, 4 figure
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Evolution of Paramagnetic Quasiparticle Excitations Emerged in the High-Field Superconducting Phase of CeCoIn5
We present In NMR measurements in a novel thermodynamic phase of CeCoIn5 in
high magnetic field, where exotic superconductivity coexists with the
incommensurate spin-density wave order. We show that the NMR spectra in this
phase provide direct evidence for the emergence of the spatially distributed
normal quasiparticle regions. The quantitative analysis for the field evolution
of the paramagnetic magnetization and newly-emerged low-energy quasiparticle
density of states is consistent with the nodal plane formation, which is
characterized by an order parameter in the Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) state. The NMR spectra also suggest that the spatially uniform
spin-density wave is induced in the FFLO phase.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let
Direct Imaging of Spatially Modulated Superfluid Phases in Atomic Fermion Systems
It is proposed that the spatially modulated superfluid phase, or the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state could be observed in resonant
Fermion atomic condensates which are realized recently. We examine optimal
experimental setups to achieve it by solving Bogoliubov-de Gennes equation both
for idealized one-dimensional and realistic three-dimensional cases. The
spontaneous modulation of this superfluid is shown to be directly imaged as the
density profiles either by optical absorption or by Stern-Gerlach experiments.Comment: 4 pages, 3 figure
Pair formation and collapse in imbalanced Fermion populations with unequal masses
We present an exact Quantum Monte Carlo study of the effect of unequal masses
on pair formation in Fermionic systems with population imbalance loaded into
optical lattices. We have considered three forms of the attractive interaction
and find in all cases that the system is unstable and collapses as the mass
difference increases and that the ground state becomes an inhomogeneous
collapsed state. We also address the question of canonical vs grand canonical
ensemble and its role, if any, in stabilizing certain phases
Noise correlations of the ultra-cold Fermi gas in an optical lattice
In this paper we study the density noise correlations of the two component
Fermi gas in optical lattices. Three different type of phases, the BCS-state
(Bardeen, Cooper, and Schieffer), the FFLO-state (Fulde, Ferrel, Larkin, and
Ovchinnikov), and BP (breach pair) state, are considered. We show how these
states differ in their noise correlations. The noise correlations are
calculated not only at zero temperature, but also at non-zero temperatures
paying particular attention to how much the finite temperature effects might
complicate the detection of different phases. Since one-dimensional systems
have been shown to be very promising candidates to observe FFLO states, we
apply our results also to the computation of correlation signals in a
one-dimensional lattice. We find that the density noise correlations reveal
important information about the structure of the underlying order parameter as
well as about the quasiparticle dispersions.Comment: 25 pages, 11 figures. Some figures are updated and text has been
modifie
Critical phenomena in a highly constrained classical spin system: Neel ordering from the Coulomb phase
Many classical, geometrically frustrated antiferromagnets have
macroscopically degenerate ground states. In a class of three-dimensional
systems, the set of degenerate ground states has power-law correlations and is
an example of a Coulomb phase. We investigate Neel ordering from such a Coulomb
phase, induced by weak additional interactions that lift the degeneracy. We
show that the critical point belongs to a universality class that is different
from the one for the equivalent transition out of the paramagnetic phase, and
that it is characterised by effective long-range interactions; alternatively,
ordering may be discontinuous. We suggest that a transition of this type may be
realised by applying uniaxial stress to a pyrochlore antiferromagnet.Comment: 4 pages, 3 figure
Generic Phase Diagram of Fermion Superfluids with Population Imbalance
It is shown by microscopic calculations for trapped imbalanced Fermi
superfluids that the gap function has always sign changes, i.e., the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state like, up to a critical imbalance
, beyond which normal state becomes stable, at temperature T=0. A phase
diagram is constructed in vs , where the BCS state without sign change
is stable only at . We reproduce the observed bimodality in the
density profile to identify its origin and evaluate as functions of
and the coupling strength. These dependencies match with the recent
experiments.Comment: 5 pages, 5 figures, replaced by the version to appear in PR
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