284 research outputs found
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
Pairing in a three component Fermi gas
We consider pairing in a three-component gas of degenerate fermions. In
particular, we solve the finite temperature mean-field theory of an interacting
gas for a system where both interaction strengths and fermion masses can be
unequal. At zero temperature we find a a possibility of a quantum phase
transition between states associated with pairing between different pairs of
fermions. On the other hand, finite temperature behavior of the three-component
system reveals some qualitative differences from the two-component gas: for a
range of parameters it is possible to have two different critical temperatures.
The lower one corresponds to a transition between different pairing channels,
while the higher one corresponds to the usual superfluid-normal transition. We
discuss how these phase transitions could be observed in ultracold gases of
fermionic atoms.Comment: 10 pages, 3 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
Molecular coupling of light with plasmonic waveguides
We use molecules to couple light into and out of microscale plasmonic
waveguides. Energy transfer, mediated by surface plasmons, from donor molecules
to acceptor molecules over ten micrometer distances is demonstrated. Also
surface plasmon coupled emission from the donor molecules is observed at
similar distances away from the excitation spot. The lithographic fabrication
method we use for positioning the dye molecules allows scaling to nanometer
dimensions. The use of molecules as couplers between far-field and near-field
light offers the advantages that no special excitation geometry is needed, any
light source can be used to excite plasmons and the excitation can be localized
below the diffraction limit. Moreover, the use of molecules has the potential
for integration with molecular electronics and for the use of molecular
self-assembly in fabrication. Our results constitute a proof-of-principle
demonstration of a plasmonic waveguide where signal in- and outcoupling is done
by molecules.Comment: 9 pages, 5 figure
Trapping of 27 bp - 8 kbp DNA and immobilization of thiol-modified DNA using dielectrophoresis
Dielectrophoretic trapping of six different DNA fragments, sizes varying from
the 27 to 8416 bp, has been studied using confocal microscopy. The effect of
the DNA length and the size of the constriction between nanoscale fingertip
electrodes on the trapping efficiency have been investigated. Using finite
element method simulations in conjunction with the analysis of the experimental
data, the polarizabilities of the different size DNA fragments have been
calculated for different frequencies. Also the immobilization of trapped
hexanethiol- and DTPA-modified 140 nm long DNA to the end of gold
nanoelectrodes was experimentally quantified and the observations were
supported by density functional theory calculations.Comment: 17 pages (1 column version), 8 figure
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