4,651 research outputs found
Analytical theory of the dressed bound state in highly polarized Fermi gases
We present an analytical treatment of a single \down atom within a Fermi sea
of \up atoms, when the interaction is strong enough to produce a bound state,
dressed by the Fermi sea. Our method makes use of a diagrammatic analysis, with
the involved diagrams taking only into account at most two particle-hole pairs
excitations. The agreement with existing Monte-Carlo results is excellent. In
the BEC limit our equation reduces exactly to the Skorniakov and
Ter-Martirosian equation. We present results when \up and \down atoms have
different masses, which is of interest for experiments in progress.Comment: 5 pages, 3 figure
On the nonlinear response of a particle interacting with fermions in a 1D lattice
By the Bethe ansatz method we study the energy dispersion of a particle
interacting by a local interaction with fermions (or hard core bosons) of equal
mass in a one dimensional lattice. We focus on the period of the Bloch
oscillations which turns out to be related to the Fermi wavevector of the Fermi
sea and in particular on how this dispersion emerges as a collective effect in
the thermodynamic limit. We show by symmetry that the dispersion is temperature
independent for a half-filled system. We also discuss the adiabatic coherent
collective response of the particle to an applied field.Comment: 4 pages, 4 figure
Direct probing of band-structure Berry phase in diluted magnetic semiconductors
We report on experimental evidence of the Berry phase accumulated by the
charge carrier wave function in single-domain nanowires made from a
(Ga,Mn)(As,P) diluted ferromagnetic semiconductor layer. Its signature on the
mesoscopic transport measurements is revealed as unusual patterns in the
magnetoconductance, that are clearly distinguished from the universal
conductance fluctuations. We show that these patterns appear in a magnetic
field region where the magnetization rotates coherently and are related to a
change in the band-structure Berry phase as the magnetization direction
changes. They should be thus considered as a band structure Berry phase
fingerprint of the effective magnetic monopoles in the momentum space. We argue
that this is an efficient method to vary the band structure in a controlled way
and to probe it directly. Hence, (Ga,Mn)As appears to be a very interesting
test bench for new concepts based on this geometrical phase.Comment: 7 pages, 6 figure
Ferromagnetic (Ga,Mn)N epilayers versus antiferromagnetic GaMnN clusters
Mn-doped wurtzite GaN epilayers have been grown by nitrogen plasma-assisted
molecular beam epitaxy. Correlated SIMS, structural and magnetic measurements
show that the incorporation of Mn strongly depends on the conditions of the
growth. Hysteresis loops which persist at high temperature do not appear to be
correlated to the presence of Mn. Samples with up to 2% Mn are purely
substitutional GaMnN epilayers, and exhibit paramagnetic
properties. At higher Mn contents, precipitates are formed which are identified
as GaMnN clusters by x-ray diffraction and absorption: this induces a
decrease of the paramagnetic magnetisation. Samples co-doped with enough Mg
exhibit a new feature: a ferromagnetic component is observed up to
K, which cannot be related to superparamagnetism of unresolved magnetic
precipitates.Comment: Revised versio
Two-dimensional universal conductance fluctuations and the electron-phonon interaction of topological surface states in Bi2Te2Se nanoribbons
The universal conductance fluctuations (UCFs), one of the most important
manifestations of mesoscopic electronic interference, have not yet been
demonstrated for the two-dimensional surface state of topological insulators
(TIs). Even if one delicately suppresses the bulk conductance by improving the
quality of TI crystals, the fluctuation of the bulk conductance still keeps
competitive and difficult to be separated from the desired UCFs of surface
carriers. Here we report on the experimental evidence of the UCFs of the
two-dimensional surface state in the bulk insulating Bi2Te2Se nanoribbons. The
solely-B\perp-dependent UCF is achieved and its temperature dependence is
investigated. The surface transport is further revealed by weak
antilocalizations. Such survived UCFs of the topological surface states result
from the limited dephasing length of the bulk carriers in ternary crystals. The
electron-phonon interaction is addressed as a secondary source of the surface
state dephasing based on the temperature-dependent scaling behavior
Evidence for Intrinsic Redshifts in Normal Spiral Galaxies
The Tully-Fisher Relationship (TFR) is utilized to identify anomalous
redshifts in normal spiral galaxies. Three redshift anomalies are identified in
this analysis: (1) Several clusters of galaxies are examined in which late type
spirals have significant excess redshifts relative to early type spirals in the
same clusters, (2) Galaxies of morphology similar to ScI galaxies are found to
have a systematic excess redshift relative to the redshifts expected if the
Hubble Constant is 72 km s-1 Mpc-1, (3) individual galaxies, pairs, and groups
are identified which strongly deviate from the predictions of a smooth Hubble
flow. These redshift deviations are significantly larger than can be explained
by peculiar motions and TFR errors. It is concluded that the redshift anomalies
identified in this analysis are consistent with previous claims for large
non-cosmological (intrinsic) redshifts.Comment: Accepted for publication at Astrophysics&Space Science. 36 pages
including 8 tables and 7 figure
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A global model of the marine ecosystem for long-term simulations: Sensitivity to ocean mixing, buoyancy forcing, particle sinking, and dissolved organic matter cycling
A new model of the marine ecosystem coupled into a global Earth System Climate Model suitable for long-term (multimillennial timescale) simulations is presented. The model is based on nitrate as the sole limiting nutrient. Prognostic equations for nutrients, phytoplankton, zooplankton, and detritus are solved online in the three-dimensional ocean circulation model component. Experiments with different parameterizations of vertical mixing, including a scheme of tidally driven mixing, changes in buoyancy forcing in the Southern Ocean, different particle sinking velocities, and the inclusion of dissolved organic matter are performed, and the results are compared with observations. The results reemphasize the roles of Southern Ocean freshwater forcing and diapycnal mixing in the low-latitude pycnocline in setting the global deep water circulation and properties. The influence of high mixing in the Southern Ocean as inferred from observations is much more limited. The deep water circulation also has a strong influence on the marine ecosystem and nutrient distributions. We demonstrate that larger values of vertical diffusion lead to a shallower nutricline due to increased upwelling. Export production and nutrient distributions respond sensitively to changes in mixing and to the ratio of particle sinking to remineralization in the upper ocean. The best fits to global measurements of temperature, salinity, deep ocean radiocarbon, mixed layer depth, nutrients, and chlorophyll are obtained for values of vertical mixing in the pycnocline of around 0.2–0.3 X 10-4 m2/s and for e-folding depth for particle remineralization of 100–200 m. A simple parameterization of dissolved organic matter dynamics increases primary production and nutrient concentrations in the upper ocean and improves chlorophyll distributions in the subtropical gyres but has no discernible influence on particulate export fluxes. Remaining model deficiencies are identified, and strategies for future model improvement are outlined
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Impact of particles on the Planck HFI detectors: Ground-based measurements and physical interpretation
The Planck High Frequency Instrument (HFI) surveyed the sky continuously from
August 2009 to January 2012. Its noise and sensitivity performance were
excellent, but the rate of cosmic ray impacts on the HFI detectors was
unexpectedly high. Furthermore, collisions of cosmic rays with the focal plane
produced transient signals in the data (glitches) with a wide range of
characteristics. A study of cosmic ray impacts on the HFI detector modules has
been undertaken to categorize and characterize the glitches, to correct the HFI
time-ordered data, and understand the residual effects on Planck maps and data
products. This paper presents an evaluation of the physical origins of glitches
observed by the HFI detectors. In order to better understand the glitches
observed by HFI in flight, several ground-based experiments were conducted with
flight-spare HFI bolometer modules. The experiments were conducted between 2010
and 2013 with HFI test bolometers in different configurations using varying
particles and impact energies. The bolometer modules were exposed to 23 MeV
protons from the Orsay IPN TANDEM accelerator, and to Am and Cm
-particle and Fe radioactive X-ray sources. The calibration data
from the HFI ground-based preflight tests were used to further characterize the
glitches and compare glitch rates with statistical expectations under
laboratory conditions. Test results provide strong evidence that the dominant
family of glitches observed in flight are due to cosmic ray absorption by the
silicon die substrate on which the HFI detectors reside. Glitch energy is
propagated to the thermistor by ballistic phonons, while there is also a
thermal diffusion contribution. The implications of these results for future
satellite missions, especially those in the far-infrared to sub-millimetre and
millimetre regions of the electromagnetic spectrum, are discussed.Comment: 11 pages, 13 figure
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