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2010-06-30 | BaFe2As2 Surface Domains and Domain Walls: Mirroring the Bulk Spin Structure | High-resolution scanning tunneling microscopy (STM) measurements on
BaFe2As2-one of the parent compounds of the iron-based superconductors-reveals
a (1x1) As-terminated unit cell on the (001) surface. However, there are
significant differences of the surface unit cell compared to the bulk: only one
of the two As atoms ... | 1006.5907v1 |
2010-07-05 | Impact of the Spin Density Wave Order on the Superconducting Gap of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ | We report a doping dependent electronic Raman scattering measurements on
iron-pnictide superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals. A
strongly anisotropic gap is found at optimal doping for x=0.065 with
$\Delta_{max}\sim 5\Delta_{min}$. Upon entering the coexistence region between
superconducting (SC)... | 1007.0720v2 |
2010-07-07 | Magnetisation distribution in the tetragonal phase of BaFe2As2 | We have determined the spatial distribution of the magnetisation induced by a
field of 9 T in the tetragonal phase of BaFe2As2 using polarised neutron
diffraction. Magnetic structure factors derived from the polarisation
dependence of the intensities of Bragg reflections were used to make a maximum
entropy reconstructi... | 1007.1116v2 |
2010-07-12 | Atomic data and spectral model for Fe III | We present new atomic data (radiative transitions rates and collision
strengths) from large scale calculations and a non-LTE spectral model for Fe
III. This model is in very good agreement with observed astronomical emission
spectra, in contrast with previous models that yield large discrepancies with
observations. The... | 1007.1960v1 |
2010-07-13 | Doping evolution of superconducting gaps and electronic densities of states in Ba(Fe1-xCox)2As2 iron pnictides | An extensive calorimetric study of the normal- and superconducting-state
properties of Ba(Fe1-xCox)2As2 is presented for 0 < x < 0.2. The normal-state
Sommerfeld coefficient increases (decreases) with Co doping for x < 0.06 (x >
0.06), which illustrates the strong competition between magnetism and
superconductivity to ... | 1007.2218v1 |
2010-07-14 | Comparative study of the electronic structures of Fe3O4 and Fe2SiO4 | The electronic properties of two spinels Fe$_3$O$_4$ and Fe$_2$SiO$_4$ are
studied by the density functional theory. The local Coulomb repulsion $U$ and
the Hund's exchange $J$ between the $3d$ electrons on iron are included. For
$U=0$, both spinels are half-metals, with the minority $t_{2g}$ states at the
Fermi level.... | 1007.2340v1 |
2010-07-17 | Pressure-induced changes in the magnetic and valence state of EuFe2As2 | We present the results of electrical resistivity, ac specific heat, magnetic
susceptibility, X-ray absorption spectroscopy (XAS) and X-ray magnetic circular
dichroism (XMCD) of the ternary iron arsenide EuFe2As2 single crystal under
pressure. Applying pressure leads to a continuous suppression of the
antiferromagnetism... | 1007.2889v2 |
2010-07-21 | Electronic structure, spin state, and magnetism of the square-lattice Mott insulator La2Co2Se2O3 from first principles | Electronic and magnetic structures of the newly synthesized cobalt
oxyselenide La2Co2Se2O3 (structurally similar to the superconducting iron
pnictides) are studied through density functional calculations. The obtained
results show that this material is a Mott insulator, and that it has a very
stable Co2+ high-spin grou... | 1007.3697v1 |
2010-07-28 | Nodes in the Order Parameter of Superconducting Iron Pnictides Observed by Infrared Spectroscopy | The temperature and frequency dependences of the conductivity are derived
from optical reflection and transmission measurements of electron doped
BaFe$_2$As$_2$ crystals and films. The data is consistent with gap nodes or
possibly a very small gap in the crossover region between these two
possibilities. This can arise ... | 1007.5215v1 |
2010-07-29 | BaFe_{1.8}Co_{0.2}As_2 thin film hybrid Josephson junctions | Josephson junctions with iron pnictides open the way for fundamental
experiments on superconductivity in these materials and their application in
superconducting devices. Here, we present hybrid Josephson junctions with a
BaFe_{1.8}Co_{0.2}As_2 thin film electrode, an Au barrier and a PbIn counter
electrode. The juncti... | 1007.5252v2 |
2010-07-30 | Reversible shift in the superconducting transition for La1.85Sr0.15CuO4 and BaFe1.8Co0.2As2 using piezoelectric substrates | The use of piezoelectric substrates enables a dynamic observation of strain
dependent properties of functional materials. Based on studies with
La1.85Sr0.15CuO4 we extended this approach to the iron arsenic superconductors
represented by BaFe2-xCoxAs2 to investigate strain driven changes in detail. We
demonstrate that ... | 1007.5454v1 |
2010-08-02 | A Search for Defect Related Ferromagnetism in SrTiO$_3$ | Room temperature ferromagnetic hysteresis is observed in commercial SrTiO$_3$
substrates purchased from a variety of suppliers. It is shown that the
ferromagnetic signal comes from the unpolished surfaces. Surface impurity
phases cannot be detected using either x-ray diffraction or energy dispersive
x-ray spectra on th... | 1008.0299v1 |
2010-08-02 | Iron substitution in NdCoAsO: crystal structure and magnetic phase diagram | The effects of replacing small amounts of Co with Fe in NdCoAsO are reported.
Polycrystalline materials with compositions NdCo1-xFexAsO (x = 0.05, 0.10,
0.15, and 0.20) are studied and the results compared to previous reports for
NdCoAsO. Rietveld analysis of powder x-ray diffraction data shows that as Fe
replaces Co o... | 1008.0304v2 |
2010-08-05 | Reciprocal Relations Between Kinetic Curves | We study coupled irreversible processes. For linear or linearized kinetics
with microreversibility, $\dot{x}=Kx$, the kinetic operator $K$ is symmetric in
the entropic inner product. This form of Onsager's reciprocal relations implies
that the shift in time, $\exp (Kt)$, is also a symmetric operator. This
generates the... | 1008.1056v2 |
2010-08-09 | Transport properties of iron-based FeTe0.5Se0.5 superconducting wire | FeTe0.5Se0.5 superconducting wires have been fabricated using ex-situ PIT
method with an Fe sheath. Among the other FeAs-based superconductor,
FeTe0.5Se0.5 has great advantage for application due to binary composition and
less toxic. Surprisingly, superconducting current was observed in the
as-fabricated wire without a... | 1008.1447v3 |
2010-08-13 | 'Genesis': A takeover from field-responsive matter? | Cairns-Smith (2008) has argued for a pre-Darwinian era, with a simpler basis
for life's functioning via primitive "crystal genes" (information transfer,
kinetic control on metabolic reactions). At the other extreme, guided by the
structural similarity of clusters in early-evolved enzymes to iron-sulphide
minerals like ... | 1008.2362v1 |
2010-08-16 | Superconductivity at 28.3 and 17.1 K in (Ca4Al2O6-y)(Fe2Pn2) (Pn = As and P) | We have successfully synthesized (Ca4Al2O6-y)(Fe2Pn2) (Pn = As and P)
(Al-42622(Pn)) using high-pressure synthesis technique. Al-42622(Pn) exhibit
superconductivity for both Pn = As and P with the transition temperatures of
28.3 K and 17.1 K, respectively. The a-lattice parameters of Al-42622(Pn) (a =
3.713 {\AA} and 3... | 1008.2586v3 |
2010-08-19 | Nodeless two-gap superconductivity in stoichiometric iron pnictide LiFeAs | The variations of in- and inter- plane London penetration depths,
$\Delta\lambda(T)$, were measured using a tunnel diode resonator in single
crystals of the intrinsic pnictide superconductor LiFeAs. This compound appears
to be in the clean limit with a residual resistivity of 4 ($T\to0$) to 8
($T_c$) $\mu \Omega\cdot$c... | 1008.3251v3 |
2010-08-19 | The Lateral Distribution Function of Coherent Radio Emission from Extensive Air Showers; Determining the Chemical Composition of Cosmic Rays | The lateral distribution function (LDF) for coherent electromagnetic
radiation from air showers initiated by ultra-high-energy cosmic rays is
calculated using a macroscopic description. A new expression is derived to
calculate the coherent radio pulse at small distances from the observer. It is
shown that for small dis... | 1008.3308v1 |
2010-08-20 | Two-band BCS superconductivity in Ba(Fe0.9Co0.1)2As2 | The conductivity and permittivity optical spectra of iron-pnictide
Ba(Fe0.9Co0.1)2As2 film (Tc=20 K) are analyzed. In the superconducting state,
at all temperatures up to Tc the temperature dependences of the magnetic field
penetration depth and of the superconducting condensate density are well
described within the ge... | 1008.3473v3 |
2010-08-23 | Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum | According to the no-hair theorem, astrophysical black holes are uniquely
described by their mass and spin. In this paper, we review a new framework for
testing the no-hair hypothesis with observations in the electromagnetic
spectrum. The approach is formulated in terms of a Kerr-like spacetime
containing a quadrupole m... | 1008.3902v2 |
2010-08-29 | Fermiology of Sr4V2O6Fe2As2: Quasi-Nested Fe vs Mott-Insulating V Orbitals | We have performed an angle-resolved photoemission spectroscopy study of a new
iron-based superconductor Sr4V2O6Fe2As2. While V 3d orbitals are found to be in
a Mott insulator state and show an incoherent peak at ~ 1 eV below the Fermi
level, the dispersive Fe 3d bands form several hole- and electron-like Fermi
surfaces... | 1008.4905v1 |
2010-08-30 | X-ray absorption by Broad Line Region Clouds in Mrk 766 | We present a new analysis of a 9-day long XMM-Newton monitoring of the Narrow
Line Seyfert 1 galaxy Mrk 766. We show that the strong changes in spectral
shape which occurred during this observation can be interpreted as due to Broad
Line Region clouds crossing the line of sight to the X-ray source. Within the
occultati... | 1008.5067v1 |
2010-09-02 | Association of oxygen vacancies with impurity metal ions in lead titanate | Thermodynamic, structural and electronic properties of isolated copper and
iron atoms as well as their complexes with oxygen vacancies in tetragonal lead
titanate are investigated by means of first principles calculations. Both
dopants exhibit a strong chemical driving force for the formation of M_Ti-V_O
(M = Cu, Fe) d... | 1009.0552v1 |
2010-09-10 | Nucleosynthesis in the Stellar Systems omega Cen and M22 | The stellar system omega Centauri is well known for the large range in
abundance among its member stars. Recent work has indicated that the globular
cluster M22 (NGC 6656) also possesses an internal abundance range, albeit
substantially smaller than that in omega Cen. Here we compare, as a function of
[Fe/H], element-t... | 1009.1955v1 |
2010-09-10 | Antiferromagnetic Critical Fluctuations in BaFe$_2$As$_2$ | Magnetic correlations near the magneto-structural phase transition in the
bilayer iron pnictide parent compound, BaFe$_2$As$_2$, are measured. In close
proximity to the antiferromagnetic phase transition in BaFe$_2$As$_2$, a
crossover to three dimensional critical behavior is anticipated and has been
preliminarily obse... | 1009.2116v1 |
2010-09-17 | Existence, character and origin of surface-related bands in the high temperature iron pnictide superconductor BaFe_{2-x}Co_{x}As_{2} | Low energy electron diffraction (LEED) experiments, LEED simulations and
finite slab density functional calculations are combined to study the cleavage
surface of Co doped BaFe_{2-x}Co_{x}As_{2} (x = 0.1, 0.17). We demonstrate that
the energy dependence of the LEED data can only be understood from a
terminating 1/2 Ba ... | 1009.3493v1 |
2010-09-20 | Electronic Structure Calculation by First Principles for Strongly Correlated Electron Systems | Recent trends of ab initio studies and progress in methodologies for
electronic structure calculations of strongly correlated electron systems are
discussed. The interest for developing efficient methods is motivated by recent
discoveries and characterizations of strongly correlated electron materials and
by requiremen... | 1009.3851v1 |
2010-09-21 | Single Crystal Growth and Characterization of the Iron-Based Superconductor KFe2As2 Synthesized by KAs Flux Method | Centimeter sized platelet single crystals of KFe2As2 were grown using a
self-flux method. An encapsulation technique using commercial stainless steel
container allowed the stable crystal growth lasting for more than 2 weeks.
Ternary K-Fe-As systems with various starting compositions were examined to
determine the optim... | 1009.4002v1 |
2010-09-22 | An ARPES view on the high-Tc problem: phonons vs spin-fluctuations | We review the search for a mediator of high-Tc superconductivity focusing on
ARPES experiment. In case of HTSC cuprates, we summarize and discuss a
consistent view of electronic interactions that provides natural explanation of
both the origin of the pseudogap state and the mechanism for high temperature
superconductiv... | 1009.4336v1 |
2010-09-30 | Mobility analysis of FeTe thin films | The Hall effect is investigated in detail for nonsuperconducting and
superconducting FeTe thin films. The Hall coefficient commonly exhibits a sign
reversal from positive in a high-temperature paramagnetic state to negative in
a low-temperature antiferromagnetic state. Phenomenological analysis by a
simple two-band Dru... | 1009.6035v2 |
2010-10-07 | A past capture event at Sagittarius A* inferred from the fluorescent X-ray emission of Sagittarius B clouds | The fluorescent X-ray emission from neutral iron in the molecular clouds (Sgr
B) indicates that the clouds are being irradiated by an external X-ray source.
The source is probably associated with the Galactic central black hole (Sgr
A*), which triggered a bright outburst one hundred years ago. We suggest that
such an o... | 1010.1312v1 |
2010-10-10 | Electronic structure of BaNi$_2$As$_2$ | BaNi$_2$As$_2$, with a first order phase transition around 131 K, is studied
by the angle-resolved photoemission spectroscopy. The measured electronic
structure is compared to the local density approximation calculations,
revealing similar large electronlike bands around $\bar{M}$ and differences
along $\bar{\Gamma}$-$... | 1010.1905v2 |
2010-10-14 | Macroscopic quantum tunneling in multigap superconducting Josephson junctions: Escape rate enhancement via quantum fluctuations of Josephson-Leggett mode | We theoretically study the macroscopic quantum tunneling (MQT) in a hetero
Josephson junction formed by a conventional single-gap superconductor and a
multi-gap one such as ${MgB}_{2}$ and iron-based superconductors. In such a
Josephson junction more than one phase differences are defined. We clarify the
quantum dynami... | 1010.2804v2 |
2010-10-12 | Revealing the degree of magnetic frustration by non-magnetic impurities | Imaging the magnetic fields around a non-magnetic impurity can provide a
clear benchmark for quantifying the degree of magnetic frustration. Focusing on
the strongly frustrated $J_1$-$J_2$ model and the spatially anisotropic
$J_{1a}$-$J_{1b}$-$J_2$ model, very distinct low energy behaviors reflect
different levels of m... | 1010.2917v2 |
2010-10-14 | Theory of Orbital Nematicity in Underdoped Iron Arsenides | Recent finding of an {\it unusual} in-plane resistivity anisotropy in the
underdoped 122-family at high temperature ($T$) suggests an orbital nematic
(ON) order, posing a challenge to extant theories. The {\it sign} of the
anisotropy contradicts expectations from weakly correlated as well as pure
spin-only nematic view... | 1010.2940v1 |
2010-10-19 | 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... | 1010.3863v1 |
2010-10-22 | Double resonance Raman study of disorder in CVD-grown single-walled carbon nanotubes | Single-walled carbon nanotubes (SWNTs) with varying degrees of disorder were
investigated using multiple-excitation Raman spectroscopy. The lattice disorder
was imparted into the nanotubes by the addition of varying amounts of sulfur to
the iron catalyst in a thermal chemical vapor deposition process. Changes in
the in... | 1010.4714v2 |
2010-10-25 | Macroscopic Model of Geomagnetic-Radiation from Air Showers, II | The generic properties of the emission of coherent radiation from a moving
charge distribution are discussed. The general structure of the charge and
current distributions in an extensive air shower are derived. These are
subsequently used to develop a very intuitive picture for the properties of the
emitted radio puls... | 1010.5268v1 |
2010-10-31 | On the Progenitors of Core-Collapse Supernovae | Theory holds that a star born with an initial mass between about 8 and 140
times the mass of the Sun will end its life through the catastrophic
gravitational collapse of its iron core to a neutron star or black hole. This
core collapse process is thought to usually be accompanied by the ejection of
the star's envelope ... | 1011.0203v1 |
2010-11-03 | Importance of Fermi surface topology for high temperature superconductivity in electron-doped iron arsenic superconductors | We used angle resolved photoemission spectroscopy and thermoelectric power to
study the poorly explored, highly overdoped side of the phase diagram of
Ba(Fe1-xCox)2As2 high temperature superconductor. Our data demonstrate that
several Lifshitz transitions - topological changes of the Fermi surface - occur
for large x. ... | 1011.0980v2 |
2010-11-04 | Electronic Structure Studies of Detwinned BaFe$_2$As$_2$ by Photoemission | We performed angle resolved photoelectron spectroscopy (ARPES) studies on
mechanically detwinned BaFe2As2. We observe clear band dispersions and the
shapes and characters of the Fermi surfaces are identified. Shapes of the two
hole pockets around the {\Gamma}-point are found to be consistent with the
Fermi surface topo... | 1011.1112v2 |
2010-11-06 | The Elemental Abundance Distributions of Milky Way Satellite Galaxies | The chemical compositions of the stars in Milky Way (MW) satellite galaxies
reveals the history of gas flows and star formation (SF) intensity. This talk
presented a Keck/DEIMOS spectroscopic survey of the Fe, Mg, Si, Ca, and Ti
abundances of nearly 3000 red giants in eight MW dwarf satellites. The
metallicity and alph... | 1011.1530v1 |
2010-11-08 | Consistent model of magnetism in ferropnictides | The discovery of superconductivity in LaFeAsO introduced the ferropnictides
as a major new class of superconducting compounds with critical temperatures
second only to cuprates. The presence of magnetic iron makes ferropnictides
radically different from cuprates. Antiferromagnetism of the parent compounds
strongly sugg... | 1011.1715v2 |
2010-11-11 | Evidence for electromagnetic granularity in polycrystalline Sm1111 iron-pnictides with enhanced phase purity | We prepared polycrystalline SmFeAsO1-xFx (Sm1111) bulk samples by sintering
and hot isostatic pressing (HIP) in order to study the effects of phase purity
and relative density on the intergranular current density. Sintered and HIPped
Sm1111 samples are denser with fewer impurity phases, such as SmOF and the
grain bound... | 1011.2547v1 |
2010-11-11 | Baryonic Bound State of Vortices in Multicomponent Superconductors | We construct a bound state of three 1/3-quantized Josephson coupled vortices
in three-component superconductors with intrinsic Josephson couplings, which
may be relevant with regard to iron-based superconductors. We find a Y-shaped
junction of three domain walls connecting the three vortices, resembling the
baryonic bo... | 1011.2552v2 |
2010-11-11 | Origin of the Ultrahigh-Energy Cosmic Rays and their Spectral Break | The energy spectrum, composition and arrival directions of ultrahigh energy
cosmic rays (UHECRs) with energy above the cosmic ray ankle, measured by the
Pierre Auger Observatory, are inconsistent if their origin is assumed to be
extragalactic. Their observed properties, however, are those expected from
UHECRs accelerat... | 1011.2672v2 |
2010-11-16 | Itinerant Spin Excitations in SrFe2As2 Measured by Inelastic Neutron Scattering | We report inelastic neutron scattering measurements of the magnetic
excitations in SrFe2As2, the parent of a family of iron-based superconductors.
The data extend throughout the Brillouin zone and up to energies of ~260meV. An
analysis with the local-moment J_1-J2 model implies very different in-plane
nearest-neighbor ... | 1011.3831v2 |
2010-11-17 | A Ray-Tracing Algorithm for Spinning Compact Object Spacetimes with Arbitrary Quadrupole Moments. I. Quasi-Kerr Black Holes | We describe a new numerical algorithm for ray tracing in the external
spacetimes of spinning compact objects characterized by arbitrary quadrupole
moments. Such spacetimes describe non-Kerr vacuum solutions that can be used to
test the no-hair theorem in conjunction with observations of accreting black
holes. They are ... | 1011.4078v1 |
2010-11-19 | Spin canting as a result of the competition between stripes and spirals in cuprates | Based on the extended Hubbard model we calculate the energy of stripe and
spiral ground states. We find that uniform spirals get favored by a large
$t'/t$ ratio but are unstable at small doping towards stripes and checkerboard
textures with spin canting. The structure of these inhomogeneities also depends
on t'/t and t... | 1011.4447v1 |
2010-11-19 | The AGB population of NGC 6822 | The metallicity gradient and the stellar distribution within the Local Group
dwarf galaxy NGC 6822 has been studied photometrically using asymptotic branch
stars (AGB). In order to study the stellar and metallicity distribution, the
carbon- and oxygen-rich AGB stars have been isolated using deep high-quality
near-infra... | 1011.4464v1 |
2010-11-22 | Orbital occupation and magnetic moments of tetrahedrally coordinated iron in CaBaFe4O7 | CaBaFe4O7 is a mixed-valent transition metal oxide having both Fe2+ and Fe3+
ions in tetrahedral coordination. Here we characterize its magnetic properties
by magnetization measurements and investigate its local electronic structure
using soft x-ray absorption spectroscopy at the Fe L2,3 edges, in combination
with mult... | 1011.4818v1 |
2010-12-03 | Magnetic and electrical properties and carrier doping effects on the Fe-based host compound Sr4Sc2Fe2As2O6 | Additional charge carriers were introduced to the iron oxyarsenide
Sr4Sc2Fe2As2O6 under a high-pressure condition, followed by measurements of
electrical resistivity, Hall coefficient, and magnetic susceptibility. The host
compound Sr4Sc2Fe2As2O6 shows metallic conductivity down to ~200 K and turns to
show a semiconduc... | 1012.0616v1 |
2010-12-10 | Density functional study of orbital-selective magnetism in FeAs-based superconductors | We performed spin-polarized density functional calculations of
lanthanide-series (Ln) iron oxypnictides LnFeAsO (Ln=La, Ce, Pr, Nd, Sm, and
Gd) with constrained Fe magnetic moments, finding that in-plane dxy and
out-of-plane dyz orbital characters are preferred for small Fe magnetic
moments. Comparison of LnFeAsO compo... | 1012.2224v2 |
2010-12-10 | Defect driven ferroelectricity and magnetism in nanocrystalline KTaO3 | Nominally pure nanocrystalline KTaO3 was thoroughly investigated by
micro-Raman and magnetic resonance spectroscopic techniques. In all samples the
defect driven ferroelectricity and magnetism are registered. Both ordering
states are suggested to appear due to the iron atoms and oxygen vacancies. The
concentration of d... | 1012.2295v1 |
2010-12-10 | The Curie temperature and exchange energy between two sublattices in half-metallic greigite Fe3S4 | High-temperature magnetic measurements have been carried out in
hydrothermally synthesized greigite (Fe3S4). We show that the Curie temperature
of greigite is significantly lower than that for its iron oxide counterpart
Fe3O4. The lower TC value (about 677 K) of greigite is in quantitative
agreement with that calculate... | 1012.2364v1 |
2010-12-12 | Thermal effects on neutrino-nucleus inelastic scattering in stellar environments | Thermal effects for inelastic neutrino-nucleus scattering off even-even
nuclei in the iron region are studied. Allowed and first-forbidden
contributions to the cross sections are calculated within the quasiparticle
random phase approximation, extended to finite temperatures within the
Thermo-Field-Dynamics formalism. T... | 1012.2543v1 |
2010-12-13 | Distinct electronic nematicities between electron and hole underdoped iron pnictides | We systematically investigated the in-plane resistivity anisotropy of
electron-underdoped $EuFe_{2-x}Co_xAs_2$ and $BaFe_{2-x}Co_xAs_2$, and
hole-underdoped $Ba_{1-x}K_xFe_2As_2$. Large in-plane resistivity anisotropy
was found in the former samples, while {\it tiny} in-plane resistivity
anisotropy was detected in the ... | 1012.2731v1 |
2010-12-14 | A detailed spectroscopic analysis of the open cluster NGC 5460 | Within the context of a large project aimed at studying early F-, A- and late
B-type stars we present the abundance analysis of the photospheres of 21
members of the open cluster NGC 5460, an intermediate age cluster (logt ~ 8.2)
previously unstudied with spectroscopy. Our study is based on medium and high
resolution s... | 1012.3050v1 |
2010-12-16 | Fabrication and some properties of biaxially aligned Sr0.6K0.4Fe2As2 superconductors by processing in high magnetic field | We fabricated the c axis and ab-plane biaxially aligned Sr0.6K0.4Fe2As2
superconductor using a two-step magnetic field procedure. The effect of
magnetic fields on the structure and superconducting properties of
Sr0.6K0.4Fe2As2 has been investigated by using X-ray diffraction and magnetic
measurements. The degree of ori... | 1012.3572v1 |
2010-12-16 | Synthesis and crystal growth of Cs0.8(FeSe0.98)2: a new iron-based superconductor with Tc=27K | We report on the synthesis of large single crystals of a new FeSe-layer
superconductor Cs0.8(FeSe0.98)2. X-ray powder diffraction, neutron
powder-diffraction and magnetization measurements have been used to compare the
crystal structure and the magnetic properties of Cs0.8(FeSe0.98)2 with those of
the recently discover... | 1012.3637v1 |
2010-12-22 | Explosive nucleosynthesis in core-collapse supernovae | The specific mechanism and astrophysical site for the production of half of
the elements heavier than iron via rapid neutron capture (r-process) remains to
be found. In order to reproduce the abundances of the solar system and of the
old halo stars, at least two components are required: the heavy r-process
nuclei (A>13... | 1012.4917v1 |
2010-12-23 | Non-collinear spin-density wave antiferromagnetism in FeAs | We present the magnetic structure of the itinerant monoarsenide, FeAs, with
the B31 structure. Powder neutron diffraction confirms incommensurate modulated
magnetism with wavevector $\mathbf{q} = (0.395\pm0.001)\mathbf{c}^*$ at 4 K,
but cannot distinguish between a simple spiral and a collinear spin-density
wave struct... | 1012.5311v2 |
2010-12-27 | Electronic Structure of KFe$_2$Se$_2$ from First Principles Calculations | Electronic structure and magnetic properties for iron-selenide KFe$_2$Se$_2$
are studied by first-principles calculations. The ground state is stripe-like
antiferromagnetic with calculated 2.26 $\mu_B$ magnetic moment on Fe atoms; and
the $J_1$, $J_2$ coupling strengths are calculated to be 0.038 eV and 0.029 eV.
The s... | 1012.5621v2 |
2010-12-29 | Electronic structures and magnetic orders of Fe-vacancies ordered ternary iron selenides TlFe$_{1.5}$Se$_2$ and AFe$_{1.5}$Se$_2$ (A=K, Rb, or Cs) | By the first-principles electronic structure calculations, we find that the
ground state of the Fe-vacancies ordered TlFe$_{1.5}$Se$_2$ is a
quasi-two-dimensional collinear antiferromagnetic semiconductor with an energy
gap of 94 meV, in agreement with experimental measurements. This
antiferromagnetic order is driven b... | 1012.6015v2 |
2011-01-10 | Monopolelike probes for quantitative magnetic force microscopy: calibration and application | A local magnetization measurement was performed with a Magnetic Force
Microscope (MFM) to determine magnetization in domains of an exchange coupled
[Co/Pt]/Co/Ru multilayer with predominant perpendicular anisotropy. The
quantitative MFM measurements were conducted with an iron filled carbon
nanotube tip, which is shown... | 1101.1804v1 |
2011-01-10 | Latest results from the Pierre Auger Observatory | Recent results obtained with the Pierre Auger Observatory are described.
These include measurements of the spectrum, anisotropies and composition of
ultra-high energy cosmic rays. The ankle of the spectrum is measured at
$4\times 10^{18}$~eV and a suppression above $3\times 10^{19}$~eV consistent
with the GZK effect is... | 1101.1825v1 |
2011-01-10 | Coexistence of Magnetism and Superconductivity in the Iron-based Compound Cs_0.8(FeSe_0.98)_2 | We report on muon-spin rotation/relaxation (\muSR), electrical resistivity,
magnetization and differential scanning calorimetry measurements performed on a
high-quality single crystal of Cs_0.8(FeSe_0.98)_2. Whereas our transport and
magnetization data confirm the bulk character of the superconducting state
below T_c =... | 1101.1873v3 |
2011-01-12 | [O/Fe] Estimates for Carbon-Enhanced Metal-Poor Stars from Near-IR Spectroscopy | We report on oxygen abundances determined from medium-resolution near-IR
spectroscopy for a sample of 57 carbon-enhanced metal-poor (CEMP) stars
selected from the Hamburg/ESO survey. The majority of our program stars exhibit
oxygen-to-iron ratios in the range +0.5 < [O/Fe]< +2.0. The [O/Fe] values for
this sample are s... | 1101.2260v1 |
2011-01-21 | A biotic cosmos demystified? | Oceanic planets formed by type Ia supernovae become spectacularly abundant as
stars cease to shine. However, the timing may not be altogether inappropriate.
Neutrino annihilation might thermally regulate iron-cored water-worlds,
sustaining habitable subglacial oceans. If dark matter and dark energy decay to
neutrinos, ... | 1101.4172v3 |
2011-01-26 | A Near-Infrared Search for Silicates in Jovian Trojan Asteroids | We obtained near-infrared (0.8 - 2.5 micron) spectra of seven Jovian Trojan
asteroids that have been formerly reported to show silicate-like absorption
features near 1 micron. Our sample includes the Trojan (1172) Aneas, which is
one of three Trojans known to possess a comet-like 10 micron emission feature,
indicative ... | 1101.5167v1 |
2011-01-30 | Controlling electrostatic co-assembly using ion-containing copolymers : from surfactants to nanoparticles | In this review, we address the issue of the electrostatic complexation
between charged-neutral diblock copolymers and oppositely charged nanocolloids.
We show that nanocolloids such as surfactant micelles and iron oxide magnetic
nanoparticles share similar properties when mixed with charged-neutral
diblocks. Above a cr... | 1101.5821v1 |
2011-01-31 | Template assisted self-assembly of individual and clusters of magnetic nanoparticles | The deliberate control over the spatial arrangement of nanostructures is the
desired goal for many applications as e.g. in data storage, plasmonics or
sensor arrays. Here we present a novel method to assist the self-assembly
process of magnetic nanoparticles. The method makes use of nanostructured
aluminum templates ob... | 1101.5899v1 |
2011-01-31 | Metastable $π$-junction between an s$_\pm$-wave and an s-wave superconductor | We examine a contact between a superconductor whose order parameter changes
sign across the Brillioun zone, and an ordinary, uniform-sign superconductor.
Within a Ginzburg-Landau type model, we find that if the the barrier between
the two superconductors is not too high, the frustration of the Josephson
coupling betwee... | 1102.0042v3 |
2011-02-01 | Ab initio study of the modification of elastic properties of alpha-iron by hydrostatic strain and by hydrogen interstitials | The effect of hydrostatic strain and of interstitial hydrogen on the elastic
properties of $\alpha$-iron is investigated using \textit{ab initio}
density-functional theory calculations. We find that the cubic elastic
constants and the polycrystalline elastic moduli to a good approximation
decrease linearly with increas... | 1102.0187v1 |
2011-02-02 | Hall effect of FeTe and Fe(Se_1-x_Te_x_) thin films | The Hall effect is investigated in thin-film samples of iron-chalcogenide
superconductors in detail. The Hall coefficient (RH) of FeTe and Fe(Se1-xTex)
exhibits a similar positive value around 300 K, indicating that the
high-temperature normal state is dominated by hole-channel transport. FeTe
exhibits a sign reversal ... | 1102.0332v1 |
2011-02-07 | Nanoscale phase separation of antiferromagnetic order and superconductivity in K$_{0.75}$Fe$_{1.75}$Se$_2$ | We report an in-plane optical spectroscopy study on the iron-selenide
superconductor K$_{0.75}$Fe$_{1.75}$Se$_2$. The measurement revealed the
development of a sharp reflectance edge below T$_c$ at frequency much smaller
than the superconducting energy gap on a relatively incoherent electronic
background, a phenomenon ... | 1102.1381v4 |
2011-02-08 | Neutron Repulsion | Earth is connected gravitationally, magnetically and electrically to its heat
source - a neutron star that is obscured from view by waste products in the
photosphere. Neutron repulsion is like the hot filament in an incandescent
light bulb. Excited neutrons are emitted from the solar core and decay into
hydrogen that g... | 1102.1499v1 |
2011-02-09 | Quasiparticle interference in antiferromagnetic parent compounds of Fe-based superconductors | Recently reported quasiparticle interference imaging in underdoped
Ca(Fe{1-x}Co{x})_2As{2} shows pronounced C{2} asymmetry that is interpreted as
an indication of an electronic nematic phase with a unidirectional electron
band, dispersive predominantly along the $b$-axis of this orthorhombic
material. On the other hand... | 1102.1930v1 |
2011-02-11 | Towards an ideal graphene-based spin-filter | The Fe$_3$O$_4$(111)/graphene/Ni(111) trilayer is proposed to be used as an
ideal spin-filtering sandwich where the half-metallic properties of magnetite
are used. Thin magnetite layers on graphene/Ni(111) were prepared via
successive oxidation of thin iron layer predeposited on graphene/Ni(111) and
formed system was i... | 1102.2367v1 |
2011-02-11 | Pressure cycle of superconducting Cs0.8Fe2Se2: a transport study | We report measurements of the temperature and pressure dependence of the
electrical resistivity of single crystalline iron-based chalcogenide
Cs0.8Fe2Se2. In this material superconductivity Tc~30K develops from a normal
state with extremely large resistivity. At ambient pressure a large "hump" in
the resistivity is obs... | 1102.2464v2 |
2011-02-14 | Common Crystalline and Magnetic Structure of superconducting A2Fe4Se5 | Single crystal neutron diffraction study has been performed on new
superconductor A2Fe4Se5, where A = Cs, K, (Tl,Rb) and (Tl,K), and the same Fe
vacancy ordered crystal structure and the same block checkerboard
antiferromagne tic order recently discovered in the K2Fe4Se5 superconductor are
observed. Thus, all known alk... | 1102.2882v2 |
2011-02-16 | Elastic properties and inter-atomic bonding in new superconductor KFe2Se2 from first principles calculations | Very recently (November, 2010, PRB, 82, 180520R) the first 122-like ternary
superconductor KxFe2Se2 with enhanced TC ~ 31K has been discovered. This
finding has stimulated much activity in search of related materials and
triggered the intense studies of their properties. Indeed already in 2010-2011
the superconductivit... | 1102.3248v1 |
2011-02-17 | Anomalous optical phonons in FeTe pnictides: spin state, magnetic order, and lattice anharmonicity | Polarized Raman-scattering spectra of non-superconducting, single-crystalline
FeTe are investigated as function of temperature. We have found a relation
between the magnitude of ordered magnetic moments and the linewidth of A1g
phonons at low temperatures. This relation is attributed to the intermediate
spin state (S=1... | 1102.3688v1 |
2011-02-23 | Absence of Tunneling Character in c-axis Transport of SmFeAsO0.85 Single Crystals | We made electrical transport measurements along the c-axis of SmFeAsO0.85
single crystals, in both three- and four-terminal configurations, focusing on
examining the possible formation of Josephson coupling between FeAs
superconducting layers. Anisotropic bulk superconductivity was observed along
the c-axis, but withou... | 1102.4645v1 |
2011-02-23 | On the nature of spectral line broadening in solar coronal dimmings | We analyze the profiles of iron emission lines observed in solar coronal
dimmings associated with coronal mass ejections, using the EUV Imaging
Spectrometer on board Hinode. We quantify line profile distortions with
empirical coefficients (asymmetry and peakedness) that compare the fitted
Gaussian to the data. We find ... | 1102.4745v1 |
2011-02-24 | Angle-resolved photoemission spectroscopy study of PrFeAsO_{0.7}: Dependence of the electronic structure on the pnictogen height | We have performed an angle-resolved photoemission spectroscopy (ARPES) study
of the iron-based superconductor PrFeAsO_{0.7} and examined the Fermi surfaces
and band dispersions near the Fermi level. Heavily hole-doped electronic states
have been observed due to the polar nature of the cleaved surfaces.
Nevertheless, we... | 1102.4907v1 |
2011-02-25 | Thermal evolution of Pt-rich FePt/Fe3O4 heterodimers studied using x-ray absorption near edge spectroscopy | FePt/Fe3O4 nanoparticles can be used as building blocks to obtain, upon
thermal annealing, magnetic nanocomposites with combined magnetic properties.
Although the pre- and post-annealed samples are usually well characterized, a
detailed investigation during annealing is necessary to reveal the role of
intermediate proc... | 1102.5321v1 |
2011-03-01 | Time-Reversal-Symmetry-Broken Superconductivity Induced by Frustrated Inter-Component Couplings | Superconductivity is associated with spontaneously broken gauge symmetry. In
some exotic superconductors the time-reversal symmetry is broken as well,
accompanied with internal magnetic field. A time-reversal symmetry broken
(TRSB) superconductivity without internal magnetic field involved can be
induced by frustrated ... | 1103.0123v2 |
2011-03-02 | Fresnel aperture diffraction: a phase-sensitive probe for superconducting pairing symmetry | Fresnel single aperture diffraction (FSAD) is proposed as a phase-sensitive
probe for pairing symmetry and Fermi surface of a superconductor. We consider
electrons injected, through a small aperture, into a thin superconducting (SC)
layer. It is shown that in case of SC gap symmetry
$\Delta(-k_x,\mathbf{k}_\parallel)=\... | 1103.0424v1 |
2011-03-04 | Nodal gap structure of BaFe_2(As_{1-x}P_x)_2 from angle-resolved thermal conductivity in a magnetic field | The structure of the superconducting order parameter in the iron-pnictide
superconductor BaFe$_2$(As$_{0.67}$P$_{0.33}$)$_2$ ($T_c=31$\,K) with line
nodes is studied by the angle-resolved thermal conductivity measurements in a
magnetic field rotated within the basal plane. We find that the thermal
conductivity displays... | 1103.0885v2 |
2011-03-06 | Basic design and engineering of normal-conducting, iron-dominated electromagnets | The intention of this course is to provide guidance and tools necessary to
carry out an analytical design of a simple accelerator magnet. Basic concepts
and magnet types will be explained as well as important aspects which should be
considered before starting the actual design phase. The central part of this
course is ... | 1103.1119v1 |
2011-03-07 | Stable magnetostructural coupling with tunable magnetoresponsive effects in hexagonal phase-transition ferromagnets | The magnetostructural coupling between the structural and the magnetic
transition plays a crucial role in magnetoresponsive effects in a
martensitic-transition system. A combination of various magnetoresponsive
effects based on this coupling may facilitate the multifunctional applications
of a host material. Here, we d... | 1103.1313v2 |
2011-03-12 | Varying Eu$^{2+}$ magnetic order in EuFe$_2$As$_2$ by chemical pressure | Among iron 122 pnictide superconductors, the EuFe$_2$As$_2$ series draws
particular interest because, in addition to superconductivity or the long-range
spin-density-wave order in the Fe subsystem, the localized Eu$^{2+}$ magnetic
moments order at low temperatures. Here we present a novel scheme of how the
spins align ... | 1103.2446v1 |
2011-03-15 | Oxygen hyperstoichiometric hexagonal ferrite CaBaFe4O7+δ(δ \approx 0.14) : coexistence of ferrimagnetism and spin glass behavior | An oxygen hyperstoichiometric ferrite CaBaFe4O7+\delta (\delta \approx 0.14)
has been synthesized using "soft" reduction of CaBaFe4O8. Like the oxygen
stoichiometric ferrimagnet CaBaFe4O7, this oxide also keeps the hexagonal
symmetry (space group: P63mc), and exhibits the same high Curie temperature of
270 K. However, ... | 1103.2939v1 |
2011-03-15 | Calorimetric Evidence of Strong-Coupling Multiband Superconductivity in Fe(Te0.57Se0.43) Single Crystal | We have investigated the specific heat of optimally-doped iron chalcogenide
superconductor Fe(Te0.57Se0.43) with a high-quality single crystal sample. The
electronic specific heat Ce of this sample has been successfully separated from
the phonon contribution using the specific heat of a non-superconducting sample
(Fe0.... | 1103.2961v1 |
2011-03-16 | Point-contact study of ReFeAs(1-x)Fx (Re=La, Sm) superconducting films | Point-contact (PC) Andreev-reflection (AR) measurements of the
superconducting gap in iron-oxipnictide ReFeAsO_{1-x}F_x (Re=La, Sm) films have
been carried out. The value of the gap is distributed in the range 2\Delta
\simeq 5-10 meV (for Re=Sm) with a maximum in the distribution around 6 meV.
Temperature dependence of... | 1103.3157v1 |
2011-03-18 | Composition of Transiting and Transiting-only super-Earths | The relatively recent detections of the first three transiting super-Earths
mark the beginning of a subfield within exoplanets that is both fruitful and
challenging. The first step into characterizing these objects is to infer their
composition given the degenerate character of the problem. The calculations
show that K... | 1103.3725v1 |
2011-03-25 | A temporal study of oxygen-rich pulsating variable AGB star, T Cep: Investigation on dust formation and dust properties | Pulsation is believed to be the leading cause of dusty mass loss from
Asymptotic Giant Branch (AGB) stars. We present a temporal study of T Cep, a
long-period Mira variable, using seven ISO SWS spectra, covering a 16-month
period over a single pulsation cycle. The observed spectral dust features
change over the pulsati... | 1103.5040v1 |
2011-03-27 | Spin-filtering and Disorder Induced Giant Magnetoresistance in Carbon Nanotubes: Ab Initio Calculations | Nitrogen-doped carbon nanotubes can provide reactive sites on the
porphyrin-like defects. It's well known that many porphyrins have transition
metal atoms, and we have explored transition metal atoms bonded to those
porphyrin-like defects in N-doped carbon nanotubes. The electronic structure
and transport are analyzed ... | 1103.5177v2 |
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