586 research outputs found
Interplay of Superconductivity and Fermi-Liquid Transport in Rh-Doped CaFe2As2 with Lattice-Collapse Transition
Ca(FeRh)As undergoes successive phase transitions with
increasing Rh doping in the 0 limit. The antiferromagnetic-metal phase
with orthorhombic structure at 0.00 0.020 is driven to a
superconducting phase with uncollapsed-tetragonal (ucT) structure at 0.020
0.024; a non-superconducting collapsed-tetragonal (cT) phase
takes over at 0.024. The breakdown of Fermi-liquid transport is
observed in the ucT phase above . In the adjacent cT phase,
Fermi-liquid transport is restored along with a disappearance of
superconductivity. This interplay of superconductivity and Fermi-liquid
transport suggests the essential role of magnetic fluctuations in the emergence
of superconductivity in doped CaFeAs.Comment: 11 pages, 4 figure
Finite volume scheme based on cell-vertex reconstructions for anisotropic diffusion problems with discontinuous coefficients
We propose a new second-order finite volume scheme for non-homogeneous and anisotropic diffusion problems based on cell to vertex reconstructions involving minimization of functionals to provide the coefficients of the cell to vertex mapping.
The method handles complex situations such as large preconditioning number diffusion matrices and very distorted meshes.
Numerical examples are provided to show the effectiveness of the method
Pressure versus concentration tuning of the superconductivity in Ba(Fe(1-x)Cox)2As2
In the iron arsenide compound BaFe2As2, superconductivity can be induced
either by a variation of its chemical composition, e.g., by replacing Fe with
Co, or by a reduction of the unit-cell volume through the application of
hydrostatic pressure p. In contrast to chemical substitutions, pressure is
expected to introduce no additional disorder into the lattice. We compare the
two routes to superconductivity by measuring the p dependence of the
superconducting transition temperature Tc of Ba(Fe(1-x)Cox)2As2 single crystals
with different Co content x. We find that Tc(p) of underdoped and overdoped
samples increases and decreases, respectively, tracking quantitatively the
Tc(x) dependence. To clarify to which extent the superconductivity relies on
distinct structural features we analyze the crystal structure as a function of
x and compare the results with that of BaFe2As2 under pressure.Comment: 14 pages, 4 figures, to be published in JPSJ Vol. 79 No. 12. The
copyright is held by The Physical Society of Japa
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Toward Interoperable Mesh, Geometry and Field Components for PDE Simulation Development
Mesh-based PDE simulation codes are becoming increasingly sophisticated and rely on advanced meshing and discretization tools. Unfortunately, it is still difficult to interchange or interoperate tools developed by different communities to experiment with various technologies or to develop new capabilities. To address these difficulties, we have developed component interfaces designed to support the information flow of mesh-based PDE simulations. We describe this information flow and discuss typical roles and services provided by the geometry, mesh, and field components of the simulation. Based on this delineation for the roles of each component, we give a high-level description of the abstract data model and set of interfaces developed by the Department of Energy's Interoperable Tools for Advanced Petascale Simulation (ITAPS) center. These common interfaces are critical to our interoperability goal, and we give examples of several services based upon these interfaces including mesh adaptation and mesh improvement
Characterization of 30 Ge enriched Broad Energy Ge detectors for GERDA Phase II
The GERmanium Detector Array (GERDA) is a low background experiment located
at the Laboratori Nazionali del Gran Sasso in Italy, which searches for
neutrinoless double beta decay of Ge into Se+2e. GERDA has
been conceived in two phases. Phase II, which started in December 2015,
features several novelties including 30 new Ge detectors. These were
manufactured according to the Broad Energy Germanium (BEGe) detector design
that has a better background discrimination capability and energy resolution
compared to formerly widely-used types. Prior to their installation, the new
BEGe detectors were mounted in vacuum cryostats and characterized in detail in
the HADES underground laboratory in Belgium. This paper describes the
properties and the overall performance of these detectors during operation in
vacuum. The characterization campaign provided not only direct input for GERDA
Phase II data collection and analyses, but also allowed to study detector
phenomena, detector correlations as well as to test the strength of pulse shape
simulation codes.Comment: 29 pages, 18 figure
Background free search for neutrinoless double beta decay with GERDA Phase II
The Standard Model of particle physics cannot explain the dominance of matter
over anti-matter in our Universe. In many model extensions this is a very
natural consequence of neutrinos being their own anti-particles (Majorana
particles) which implies that a lepton number violating radioactive decay named
neutrinoless double beta () decay should exist. The detection
of this extremely rare hypothetical process requires utmost suppression of any
kind of backgrounds.
The GERDA collaboration searches for decay of Ge
(^{76}\rm{Ge} \rightarrow\,^{76}\rm{Se} + 2e^-) by operating bare detectors
made from germanium with enriched Ge fraction in liquid argon. Here, we
report on first data of GERDA Phase II. A background level of
cts/(keVkgyr) has been achieved which is the world-best if
weighted by the narrow energy-signal region of germanium detectors. Combining
Phase I and II data we find no signal and deduce a new lower limit for the
half-life of yr at 90 % C.L. Our sensitivity of
yr is competitive with the one of experiments with
significantly larger isotope mass.
GERDA is the first experiment that will be background-free
up to its design exposure. This progress relies on a novel active veto system,
the superior germanium detector energy resolution and the improved background
recognition of our new detectors. The unique discovery potential of an
essentially background-free search for decay motivates a
larger germanium experiment with higher sensitivity.Comment: 14 pages, 9 figures, 1 table; ; data, figures and images available at
http://www.mpi-hd.mpg/gerda/publi
The first search for bosonic super-WIMPs with masses up to 1 MeV/c with GERDA
We present the first search for bosonic super-WIMPs as keV-scale dark matter
candidates performed with the GERDA experiment. GERDA is a neutrinoless
double-beta decay experiment which operates high-purity germanium detectors
enriched in Ge in an ultra-low background environment at the Laboratori
Nazionali del Gran Sasso (LNGS) of INFN in Italy. Searches were performed for
pseudoscalar and vector particles in the mass region from 60 keV/c to 1
MeV/c. No evidence for a dark matter signal was observed, and the most
stringent constraints on the couplings of super-WIMPs with masses above 120
keV/c have been set. As an example, at a mass of 150 keV/c the most
stringent direct limits on the dimensionless couplings of axion-like particles
and dark photons to electrons of and
at 90% credible interval,
respectively, were obtained.Comment: 6 pages, 3 figures, submitted to Physical Review Letters, added list
of authors, updated ref. [21
decay of Ge into excited states with GERDA Phase I
Two neutrino double beta decay of Ge to excited states of Se
has been studied using data from Phase I of the GERDA experiment. An array
composed of up to 14 germanium detectors including detectors that have been
isotopically enriched in Ge was deployed in liquid argon. The analysis
of various possible transitions to excited final states is based on coincidence
events between pairs of detectors where a de-excitation ray is
detected in one detector and the two electrons in the other.
No signal has been observed and an event counting profile likelihood analysis
has been used to determine Frequentist 90\,\% C.L. bounds for three
transitions: : 1.6 yr,
: 3.7 yr and : 2.3 yr. These bounds are more
than two orders of magnitude larger than those reported previously. Bayesian
90\,\% credibility bounds were extracted and used to exclude several models for
the transition
Hierarchical Structure Formation and Modes of Star Formation in Hickson Compact Group 31
The handful of low-mass, late-type galaxies that comprise Hickson Compact
Group 31 is in the midst of complex, ongoing gravitational interactions,
evocative of the process of hierarchical structure formation at higher
redshifts. With sensitive, multicolor Hubble Space Telescope imaging, we
characterize the large population of <10 Myr old star clusters that suffuse the
system. From the colors and luminosities of the young star clusters, we find
that the galaxies in HCG 31 follow the same universal scaling relations as
actively star-forming galaxies in the local Universe despite the unusual
compact group environment. Furthermore, the specific frequency of the globular
cluster system is consistent with the low end of galaxies of comparable masses
locally. This, combined with the large mass of neutral hydrogen and tight
constraints on the amount of intragroup light, indicate that the group is
undergoing its first epoch of interaction-induced star formation. In both the
main galaxies and the tidal-dwarf candidate, F, stellar complexes, which are
sensitive to the magnitude of disk turbulence, have both sizes and masses more
characteristic of z=1-2 galaxies. After subtracting the light from compact
sources, we find no evidence for an underlying old stellar population in F --
it appears to be a truly new structure. The low velocity dispersion of the
system components, available reservoir of HI, and current star formation rate
of ~10 solar masses per year, indicate that HCG31 is likely to both exhaust its
cold gas supply and merge within ~1 Gyr. We conclude that the end product will
be an isolated, X-ray-faint, low-mass elliptical.Comment: 24 pages, 14 figures (including low resolution versions of color
images), latex file prepared with emulateapj. Accepted for publication by the
Astronomical Journa
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