7,793 research outputs found
Density response of a trapped Fermi gas: a crossover from the pair vibration mode to the Goldstone mode
We consider the density response of a trapped two-component Fermi gas.
Combining the Bogoliubov-deGennes method with the random phase approximation
allows the study of both collective and single particle excitations.
Calculating the density response across a wide range of interactions, we
observe a crossover from a weakly interacting pair vibration mode to a strongly
interacting Goldstone mode. The crossover is associated with a depressed
collective mode frequency and an increased damping rate, in agreement with
density response experiments performed in strongly interacting atomic gases.Comment: 14 pages, 8 figure
Fast trimers in one-dimensional extended Fermi-Hubbard model
We consider a one-dimensional two component extended Fermi-Hubbard model with
nearest neighbor interactions and mass imbalance between the two species. We
study the stability of trimers, various observables for detecting them, and
expansion dynamics. We generalize the definition of the trimer gap to include
the formation of different types of clusters originating from nearest neighbor
interactions. Expansion dynamics reveal rapidly propagating trimers, with
speeds exceeding doublon propagation in strongly interacting regime. We present
a simple model for understanding this unique feature of the movement of the
trimers, and we discuss the potential for experimental realization.Comment: 10 pages, 10 figure
Pairing gap and in-gap excitations in trapped fermionic superfluids
We consider trapped atomic Fermi gases with Feshbach-resonance enhanced
interactions in pseudogap and superfluid temperatures. We calculate the
spectrum of RF(or laser)-excitations for transitions that transfer atoms out of
the superfluid state. The spectrum displays the pairing gap and also the
contribution of unpaired atoms, i.e. in-gap excitations. The results support
the conclusion that a superfluid, where pairing is a many-body effect, was
observed in recent experiments on RF spectroscopy of the pairing gap.Comment: Journal versio
Hartree shift in unitary Fermi gases
The Hartree energy shift is calculated for a unitary Fermi gas. By including
the momentum dependence of the scattering amplitude explicitly, the Hartree
energy shift remains finite even at unitarity. Extending the theory also for
spin-imbalanced systems allows calculation of polaron properties. The results
are in good agreement with more involved theories and experiments.Comment: 31 pages, many figure
Strongly interacting Fermi gases with density imbalance
We consider density-imbalanced Fermi gases of atoms in the strongly
interacting, i.e. unitarity, regime. The Bogoliubov-deGennes equations for a
trapped superfluid are solved. They take into account the finite size of the
system, as well as give rise to both phase separation and FFLO type
oscillations in the order parameter. We show how radio-frequency spectroscopy
reflects the phase separation, and can provide direct evidence of the FFLO-type
oscillations via observing the nodes of the order parameter.Comment: Added one reference. Published in PR
Boundedness and unboundedness results for some maximal operators on functions of bounded variation
We characterize the space of functions of bounded variation on an
arbitrary interval , in terms of a uniform boundedness
condition satisfied by the local uncentered maximal operator from
into the Sobolev space .
By restriction, the corresponding characterization holds for . We
also show that if is open in , then boundedness from
into fails for the local directional maximal operator
, the local strong maximal operator , and the iterated local
directional maximal operator . Nevertheless, if
satisfies a cone condition, then boundedly, and the
same happens with , , and .Comment: 15 page
Pairing based cooling of Fermi gases
We propose a pairing-based method for cooling an atomic Fermi gas. A three
component (labels 1, 2, 3) mixture of Fermions is considered where the
components 1 and 2 interact and, for instance, form pairs whereas the component
3 is in the normal state. For cooling, the components 2 and 3 are coupled by an
electromagnetic field. Since the quasiparticle distributions in the paired and
in the normal states are different, the coupling leads to cooling of the normal
state even when initially (notation ).
The cooling efficiency is given by the pairing energy and by the linewidth of
the coupling field. No superfluidity is required: any type of pairing, or other
phenomenon that produces a suitable spectral density, is sufficient. In
principle, the paired state could be cooled as well but this requires
. The method has a conceptual analogy to cooling based on
superconductor -- normal metal (SN) tunneling junctions. Main differences arise
from the exact momentum conservation in the case of the field-matter coupling
vs. non-conservation of momentum in the solid state tunneling process.
Moreover, the role of processes that relax the energy conservation requirement
in the tunneling, e.g. thermal fluctuations of an external reservoir, is now
played by the linewidth of the field. The proposed method should be
experimentally feasible due to its close connection to RF-spectroscopy of
ultracold gases which is already in use.Comment: Journal version 4 pages, 4 figure
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