1,882 research outputs found
Density-wave phases of dipolar fermions in a bilayer
We investigate the phase diagram of dipolar fermions with aligned dipole
moments in a two-dimensional (2D) bilayer. Using a version of the
Singwi-Tosi-Land-Sjolander scheme recently adapted to dipolar fermions in a
single layer [M. M. Parish and F. M. Marchetti, Phys. Rev. Lett. 108, 145304
(2012)], we determine the density-wave instabilities of the bilayer system
within linear response theory. We find that the bilayer geometry can stabilize
the collapse of the 2D dipolar Fermi gas with intralayer attraction to form a
new density wave phase that has an orientation perpendicular to the density
wave expected for strong intralayer repulsion. We thus obtain a quantum phase
transition between stripe phases that is driven by the interplay between strong
correlations and the architecture of the low dimensional system.Comment: 5 pages, 3 figure
Dipolar fermions in a multilayer geometry
We investigate the behavior of identical dipolar fermions with aligned dipole
moments in two-dimensional multilayers at zero temperature. We consider density
instabilities that are driven by the attractive part of the dipolar interaction
and, for the case of bilayers, we elucidate the properties of the stripe phase
recently predicted to exist in this interaction regime. When the number of
layers is increased, we find that this "attractive" stripe phase exists for an
increasingly larger range of dipole angles, and if the interlayer distance is
sufficiently small, the stripe phase eventually spans the full range of angles,
including the situation where the dipole moments are aligned perpendicular to
the planes. In the limit of an infinite number of layers, we derive an analytic
expression for the interlayer effects in the density-density response function
and, using this result, we find that the stripe phase is replaced by a collapse
of the dipolar system.Comment: 9 pages, 8 figure
Leggett mode in a strong-coupling model of iron arsenide superconductors
Using a two-orbital model of the superconducting phase of the pnictides, we
compute the spectrum of the Leggett mode -- a collective excitation of the
phase of the superconducting gap known to exist in multi-gap superconductors --
for different possible symmetries of the superconducting order parameter.
Specifically, we identify the small regions of parameter space where the
Leggett mode lies below the two-particle continuum, and hence should be visible
as a sharp resonance peak. We discuss the possible utility of the Leggett mode
in distinguishing different momentum dependencies of the superconducting gap.
We argue that the observation of a sharp Leggett mode would be consistent with
the presence of strong electron-electron correlations in iron-based
superconductors. We also emphasize the importance of the orbital character of
the Leggett mode, which can result in an experimental observation of the mode
in channels other than
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Measured noise reductions resulting from modified approach procedures for business jet aircraft
Five business jet airplanes were flown to determine the noise reductions that result from the use of modified approach procedures. The airplanes tested were a Gulfstream 2, JetStar, Hawker Siddeley 125-400, Sabreliner-60 and LearJet-24. Noise measurements were made 3, 5, and 7 nautical miles from the touchdown point. In addition to a standard 3 deg glide slope approach, a 4 deg glide slope approach, a 3 deg glide slope approach in a low-drag configuration, and a two-segment approach were flown. It was found that the 4 deg approach was about 4 EPNdB quieter than the standard 3 deg approach. Noise reductions for the low-drag 3 deg approach varied widely among the airplanes tested, with an average of 8.5 EPNdB on a fleet-weighted basis. The two-segment approach resulted in noise reductions of 7 to 8 EPNdB at 3 and 5 nautical miles from touchdown, but only 3 EPNdB at 7 nautical miles from touchdown when the airplanes were still in level flight prior to glide slope intercept. Pilot ratings showed progressively increasing workload for the 4 deg, low-drag 3 deg, and two-segment approaches
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