5,192 research outputs found
Strongly spin-polarized current generated in Zeeman-split unconventional superconductors
We consider a thin-film normal metal/superconductor junction in the presence
of an externally applied in-plane magnetic field for several symmetries of the
superconducting order parameter. For p-wave superconductors, a strongly
spin-polarized current emerges due to an interplay between the nodal structure
of the superconducting order parameter, the existence or non-existence of
zero-energy surface states, and the Zeeman-splitting of the bands which form
superconductivity. Thus, the polarization depends strongly on the orbital
symmetry of the superconducting state. Our findings suggest a mechanism for
obtaining fully spin-polarized currents crucially involving zero-energy surface
states, not present in s-wave superconductors.Comment: 5 pages, 5 figures. Accepted for publication in Phys. Rev.
The Limits of Quintessence
We present evidence that the simplest particle-physics scalar-field models of
dynamical dark energy can be separated into distinct behaviors based on the
acceleration or deceleration of the field as it evolves down its potential
towards a zero minimum. We show that these models occupy narrow regions in the
phase-plane of w and w', the dark energy equation-of-state and its
time-derivative in units of the Hubble time. Restricting an energy scale of the
dark energy microphysics limits how closely a scalar field can resemble a
cosmological constant. These results, indicating a desired measurement
resolution of order \sigma(w')\approx (1+w), define firm targets for
observational tests of the physics of dark energy.Comment: 4 pages, 2 figure
Gravitational Wave Sirens as a Triple Probe of Dark Energy
Gravitational wave standard sirens have been considered as precision distance
indicators to high redshift; however, at high redshift standard sirens or
standard candles such as supernovae suffer from lensing noise. We investigate
lensing noise as a signal instead and show how measurements of the maximum
demagnification (minimum convergence) probe cosmology in a highly complementary
manner to the distance itself. Revisiting the original form for minimum
convergence we quantify the bias arising from the commonly used approximation.
Furthermore, after presenting a new lensing probability function we discuss how
the width of the lensed standard siren amplitude distribution also probes
growth of structure. Thus standard sirens and candles can serve as triple
probes of dark energy, measuring both the cosmic expansion history and growth
history.Comment: 7 pages, 5 figures; v2 minor changes matching published versio
Galaxy Peculiar Velocities From Large-Scale Supernova Surveys as a Dark Energy Probe
Upcoming imaging surveys such as the Large Synoptic Survey Telescope will
repeatedly scan large areas of sky and have the potential to yield
million-supernova catalogs. Type Ia supernovae are excellent standard candles
and will provide distance measures that suffice to detect mean pairwise
velocities of their host galaxies. We show that when combining these distance
measures with photometric redshifts for either the supernovae or their host
galaxies, the mean pairwise velocities of the host galaxies will provide a dark
energy probe which is competitive with other widely discussed methods. Adding
information from this test to type Ia supernova photometric luminosity
distances from the same experiment, plus the cosmic microwave background power
spectrum from the Planck satellite, improves the Dark Energy Task Force Figure
of Merit by a factor of 1.8. Pairwise velocity measurements require no
additional observational effort beyond that required to perform the traditional
supernova luminosity distance test, but may provide complementary constraints
on dark energy parameters and the nature of gravity. Incorporating additional
spectroscopic redshift follow-up observations could provide important dark
energy constraints from pairwise velocities alone. Mean pairwise velocities are
much less sensitive to systematic redshift errors than the luminosity distance
test or weak lensing techniques, and also are only mildly affected by
systematic evolution of supernova luminosity.Comment: 18 pages; 4 figures; 4 tables; replaced to match the accepted versio
Spontaneously Localized Photonic Modes Due to Disorder in the Dielectric Constant
We present the first experimental evidence for the existence of strongly
localized photonic modes due to random two dimensional fluctuations in the
dielectric constant. In one direction, the modes are trapped by ordered Bragg
reflecting mirrors of a planar, one wavelength long, microcavity. In the cavity
plane, they are localized by disorder, which is due to randomness in the
position, composition and sizes of quantum dots located in the anti-node of the
cavity. We extend the theory of disorder induced strong localization of
electron states to optical modes and obtain quantitative agreement with the
main experimental observations.Comment: 6 page
Faraday Rotation Spectroscopy of Quantum-Dot Quantum Wells
Time-resolved Faraday rotation studies of CdS/CdSe/CdS quantum-dot quantum
wells have recently shown that the Faraday rotation angle exhibits several
well-defined resonances as a function of probe energy close to the absorption
edge. Here, we calculate the Faraday rotation angle from the eigenstates of the
quantum-dot quantum well obtained with k.p theory. We show that the large
number of narrow resonances with comparable spectral weight observed in
experiment is not reproduced by the level scheme of a quantum-dot quantum well
with perfect spherical symmetry. A simple model for broken spherical symmetry
yields results in better qualitative agreement with experiment.Comment: 9 pages, 4 figure
Comparison of organoleptic acceptability of liquid and fresh diets
Organoleptic acceptability of liquid and fresh diets for space flight feedin
Tunneling currents in ferromagnetic systems with multiple broken symmetries
SHORTENED ABSTRACT: A system exhibiting multiple simultaneously broken
symmetries offers the opportunity to influence physical phenomena such as
tunneling currents by means of external control parameters. In this paper, we
consider the broken SU(2) (internal spin) symmetry of ferromagnetic systems
coexisting with \textit{i)} the broken U(1) symmetry of superconductors and
\textit{ii)} the broken spatial inversion symmetry induced by a Rashba term in
a spin-orbit coupling Hamiltonian. In order to study the effect of these broken
symmetries, we consider tunneling currents that arise in two different systems;
tunneling junctions consisting of non-unitary spin-triplet ferromagnetic
superconductors and junctions consisting of ferromagnets with spin-orbit
coupling.Comment: Accepted for publication in Phys. Rev.
The biochemical, physiological, and metabolic evaluation of human subjects in a life support systems evaluator and on a liquid food diet Final report, 12 Jun. 1964 - 23 Feb. 1965
Biochemical, physiological, and metabolic analysis of subjects in life support system on liquid food diets during space environment simulatio
Josephson effect in thin-film superconductor/insulator/superconductor junctions with misaligned in-plane magnetic fields
We study a tunnel junction consisting of two thin-film s-wave superconductors
separated by a thin, insulating barrier in the presence of misaligned in-plane
exchange fields. We find an interesting interplay between the superconducting
phase difference and the relative orientation of the exchange fields,
manifested in the Josephson current across the junction. Specifically, this may
be written , where
I_0 and I_m are constants, and is the relative orientation of the
exchange fields while is the superconducting phase difference.
Similar results have recently been obtained in other S/I/S junctions coexisting
with helimagnetic or ferromagnetic order. We calculate the superconducting
order parameter self-consistently, and investigate quantitatively the effect
which the misaligned exchange fields constitute on the Josephson current, to
see if I_m may have an appreciable effect on the Josephson current. It is found
that I_0 and I_m become comparable in magnitude at sufficiently low
temperatures and fields close to the critical value, in agreement with previous
work. From our analytical results, it then follows that the Josephson current
in the present system may be controlled in a well-defined manner by a rotation
of the exchange fields on both sides of the junction. We discuss a possible
experimental realization of this proposition.Comment: 8 pages, 8 figures. Accepted for publication in Phys. Rev.
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